Micro-electromechanical resonators

Abstract

To enable temperature stability and wear resistance, for example.SOLUTION: In a MEMS device having a substrate and a movable micromachined member, a mechanical structure secures the movable micromachined member to the substrate, thermally isolates the movable micromachined member from the substrate, and provides a conduction path to enable heating of the movable micromachined member to a temperature of at least 300°C.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority to and incorporates, by reference, U.S. Provisional Patent Application No. 62 / 181,767, filed June 19, 2015, and U.S. Provisional Patent Application No. 62 / 183,689, filed June 23, 2015. This application also incorporates, by reference, U.S. Provisional Patent Application No. 61 / 937,601, filed February 9, 2014, and U.S. Patent Application No. 14 / 617,753, filed February 9, 2015.

[0002] Technical field The disclosures herein relate to the field of micro-electromechanical systems (MEMS), and more particularly to resonant MEMS structures.

[0003] Brief explanation of the drawing Various embodiments disclosed herein are shown in the following accompanying drawings, not as limitations, but as examples. [Brief explanation of the drawing]

[0004] [Figure 1A] Various physical, electrical, and TCF industrial design aspects of exemplary piezoelectric MEMS resonators having at least two degenerate doped silicon layers are shown. [Figure 1B] Various physical, electrical, and TCF industrial design aspects of exemplary piezoelectric MEMS resonators having at least two degenerate doped silicon layers are shown. [Figure 1C] Various physical, electrical, and TCF industrial design aspects of exemplary piezoelectric MEMS resonators having at least two degenerate doped silicon layers are shown. [Figure 2A] Examples of positive and negative first and second-order frequency temperature coefficients (TCFs) are shown, as well as positive and negative zero-order TCFs (i.e., temperature-independent frequency offsets). [Figure 2B]This document describes an embodiment of a resonant structure composed of one or more materials that allows control of the primary and secondary resonator frequency temperature coefficients. [Figure 2C] This document describes an embodiment of a resonant structure composed of one or more materials that allows control of the primary and secondary resonator frequency temperature coefficients. [Figure 2D] This document describes an embodiment of a resonant structure composed of one or more materials that allows control of the primary and secondary resonator frequency temperature coefficients. [Figure 2E] This document describes an embodiment of a resonant structure composed of one or more materials that allows control of the primary and secondary resonator frequency temperature coefficients. [Figure 2F] This describes one embodiment of a resonator having a degenerate doped semiconductor layer in which the dopant concentration and / or type is non-uniform across the resonator body. [Figure 2G] An embodiment of a resonator having a region inside or above the resonator of locally deposited or patterned material having desirable properties is shown. [Figure 2H] Figures 2B to 2G show resonator embodiments and examples of engineered TCFs in other embodiments disclosed herein. [Figure 2I] Figure 2E shows a resonator embodiment in which the conductive layer is manufactured to be sufficiently thin so that its contribution to the TCF of the composite structure can be ignored. [Figure 2J] This document describes one embodiment of a MEMS resonator having degenerate-doped single-crystal silicon layered with aluminum nitride, sandwiched between upper and lower electrodes. [Figure 3] This shows one embodiment of a MEMS system in which the resonator, along with a temperature-sensing element and a heater, is manufactured together on a single substrate (the temperature-sensing element and / or heater can be optionally omitted in alternative embodiments). [Figure 4A] This document describes an embodiment of a MEMS system in which a temperature-stable MEMS resonator is combined with further active temperature compensation for improved frequency stability with respect to temperature. [Figure 4B]Shows an embodiment of a MEMS system in which a temperature-stabilized MEMS resonator is combined with additional active temperature compensation for improved frequency stability with respect to temperature. [Figure 4C] Shows an embodiment of a MEMS system in which a temperature-stabilized MEMS resonator is combined with additional active temperature compensation for improved frequency stability with respect to temperature. [Figure 4D] Shows an embodiment of a MEMS system in which a temperature-stabilized MEMS resonator is combined with additional active temperature compensation for improved frequency stability with respect to temperature. [Figure 4E] Shows an embodiment of a MEMS system in which a temperature-stabilized MEMS resonator is combined with additional active temperature compensation for improved frequency stability with respect to temperature. [Figure 4F] Shows an embodiment of a MEMS system in which a temperature-stabilized MEMS resonator is combined with additional active temperature compensation for improved frequency stability with respect to temperature. [Figure 4G] Shows an embodiment of a MEMS system in which a temperature-stabilized MEMS resonator is combined with additional active temperature compensation for improved frequency stability with respect to temperature. [Figure 4H] Shows an embodiment of a MEMS system in which a temperature-stabilized MEMS resonator is combined with additional active temperature compensation for improved frequency stability with respect to temperature. [Figure 4I] Shows an embodiment of a MEMS system in which a temperature-stabilized MEMS resonator is combined with additional active temperature compensation for improved frequency stability with respect to temperature. [Figure 5A] Shows one embodiment of a degeneratively doped silicon MEMS resonator integrated with one or more components of an active temperature compensation system. [Figure 5B] Shows an example of a temperature compensation operation in the embodiment of FIG. 5A. [Figure 6] Shows various options for integrating a temperature sensor in an oscillator system having dual silicon resonators. [Figure 7] This document illustrates an exemplary process for fabricating MEMS thermistors and dual-silicon MEMS resonators within adjacent regions of the same SOI substrate. [Figure 8] An illustrative interconnection configuration is shown within a dual silicon resonator having a further low-concentration doped (or undoped) single-crystal silicon thermistor layer as part of the resonator structure. [Figure 9A] An embodiment of a degenerate doped semiconductor (DDS) resonator having one or more of the features described in relation to Figures 1A to 5B is shown. [Figure 9B] Figure 9A shows an illustrative finite element model of a DDS resonator. [Figure 10A] This example does not cover all aspects of dual silicon resonator geometry and design. [Figure 10B] This example does not cover all aspects of dual silicon resonator geometry and design. [Figure 10C] This example does not cover all aspects of dual silicon resonator geometry and design. [Figure 10D] This example does not cover all aspects of dual silicon resonator geometry and design. [Figure 10E] This example does not cover all aspects of dual silicon resonator geometry and design. [Figure 10F] This example does not cover all aspects of dual silicon resonator geometry and design. [Figure 10G] This example does not cover all aspects of dual silicon resonator geometry and design. [Figure 10H] This example does not cover all aspects of dual silicon resonator geometry and design. [Figure 10I] This example does not cover all aspects of dual silicon resonator geometry and design. [Figure 11A]Embodiments of a dual silicon resonator having one or more metal layers or silicides are shown to improve the conductivity of the electrodes and / or to function as a seed bed for improving the structuring of the material of the internal piezoelectric layer. [Figure 11B] Embodiments of a dual silicon resonator having one or more metal layers or silicides are shown to improve the conductivity of the electrodes and / or to function as a seed bed for improving the structuring of the material of the internal piezoelectric layer. [Figure 12A] Figure 1A shows an alternative material laminate having three layers, along with an additional metal layer. [Figure 12B] Figure 1A shows an alternative material laminate having three layers, along with an additional metal layer. [Figure 13A] This document describes an embodiment of a symmetrical dual-silicon material laminate that avoids surface tension imbalance and the resulting structural warping. [Figure 13B] This document describes an embodiment of a symmetrical dual-silicon material laminate that avoids surface tension imbalance and the resulting structural warping. [Figure 14] This specification illustrates examples of micro-machined components (or structures) within a micro-electromechanical system (MEMS) that can be heated or superheated using various techniques and circuit configurations disclosed herein. [Figure 15A] A profile diagram of an exemplary MEMS device having a DDS resonator along with structural interconnects that allow for Joule heating during manufacturing is shown. [Figure 15B] An embodiment of post-encapsulation Joule-heated MEMS is shown in which conductive vias extend through a sealed encapsulation lid configuration to establish electrical contact with a conductive anchoring structure. [Figure 15C] An alternative embodiment is shown in which conductive vias extend through the apparatus substrate (e.g., bulk semiconductor) to enable the flow of Joule heating current through the DDS resonator. [Figure 16A] An example of a bulk tether is shown, illustrating an embodiment of a multifunctional tether structure. [Figure 16B]An example of a composite tether is shown, illustrating an embodiment of a multifunctional tether structure. [Figure 16C] An example of an extension path tether is shown, illustrating an embodiment of a multifunctional tether structure. [Figure 16D] An illustrative thermal profile is shown, achieved by conducting a DC or AC Joule heating current through a movable micro-machined component via an anchor and a folded tether. [Figure 17] Another Joule heating MEMS embodiment is shown in which individual pairs of "flexible" tethers are provided to conduct a Joule heating current to a movable micro-machined component, so that each tether pair forms a dedicated heating port. [Figure 18A] An exemplary capacitively coupled heating configuration is shown in which electrodes, functioning as drive and / or sensing electrodes, play a dual role as a radio frequency (RF) energy input driving an AC Joule heating current within a movable micro-machined component. [Figure 18B] An exemplary capacitively coupled heating configuration is shown in which electrodes, functioning as drive and / or sensing electrodes, play a dual role as a radio frequency (RF) energy input driving an AC Joule heating current within a movable micro-machined component. [Figure 19A] This describes a Joule heating embodiment in which energy is supplied to individual layers of a multilayer MEMS resonator by conduction or capacitance. [Figure 19B] This describes an alternative heating configuration where Joule heating is primarily supplied within the patterned electrode layer of a dual silicon resonator. [Figure 20] Another embodiment shows an RF energy source coupled across the outer layer of a movable micromachined component, as shown in Figure 19A. [Figure 21] An encapsulated or chip-scale MEMS package is shown, comprising a MEMS die (for example, having a movable micro-machined component formed on its upper surface) and a control die. [Figure 22]Figure 22 shows one embodiment of a programmable heating controller that can be used to implement the programmable heating control circuit. [Figure 23] This describes a configuration in which multiple heating power drivers within an external heating controller can be coupled to individual singulated or on-wafer MEMS devices. [Figure 24A] Figures 22 and 23 show exemplary heating power profiles that can be generated in an external or in-situ heating controller or any other feasible heating source, along with exemplary temperatures generated within a movable micro-machined component. [Figure 24B] This shows the waveform shaping of exemplary power pulses that can be applied to achieve controlled cooling and / or heating of a MEMS structure. [Figure 25] This example illustrates the process for a packaged MEMS device in which an oven reflow operation is performed to merge two separate terminals forming a heating port into a single operable control terminal. [Figure 26] An illustrative heating port configuration in a packaged MEMS device is shown, having two front terminals and one rear terminal for enabling Joule heating / overheating. [Figure 27A] An illustrative circuit model corresponding to the packaged MEMS device in Figure 26 during heating / overheating operation is shown. [Figure 27B] This shows an illustrative circuit model corresponding to the packaged MEMS device in Figure 26 during runtime operation. [Figure 28A] This illustrates an illustrative electrical interconnection between an encapsulation-level through-silicon via (TSV) and a piezoelectrically operated resonator electrode, enabling both package-level terminal interconnection (i.e., in the subsequent packaging step) and post-encapsulation Joule heating of the MEMS resonator. [Figure 28B] This illustrates an illustrative electrical interconnection between an encapsulation-level through-silicon via (TSV) and a piezoelectrically operated resonator electrode, enabling both package-level terminal interconnection (i.e., in the subsequent packaging step) and post-encapsulation Joule heating of the MEMS resonator. [Figure 29A] This describes an alternative terminal reduction scheme in which three or more encapsulated-level terminals are merged into the enclosure within the package housing in order to expose only two electrically independent package-level terminals. [Figure 29B] This describes an alternative terminal reduction scheme in which three or more encapsulated-level terminals are merged into the enclosure within the package housing in order to expose only two electrically independent package-level terminals. [Figure 30] This demonstrates heating of a MEMS resonator via a laser beam that is selectively absorbed by DDS in relation to the lid and substrate, which are part of the sealed encapsulation. [Figure 31A] The fluctuation of the electroactive dopant concentration in the DDS as a function of temperature during the heating cycle is shown. [Figure 31B] This shows the cooling rate dependence of the electroactive dopant concentration. [Figure 32A] This exhibits a decrease in the room-temperature resonance frequency accompanied by an increase in the electroactive dopant concentration. [Figure 32B] This shows the dependence of the room-temperature resonant frequency of a MEMS resonator housing a DDS on both the time and temperature of the heating cycle in which the resonator is rapidly cooled thereafter. [Figure 33] This shows the sequence of heating pulses applied to the MEMS resonator, the corresponding average temperature of the MEMS structure in each cycle, and the resulting resonant frequency of one of the MEMS resonator's intrinsic modes at or near room temperature after each heating pulse. [Figure 34] This document presents an automated closed-loop algorithm for trimming the frequencies of one or more resonant modes of a MEMS structure at one or more temperatures. [Figure 35] The following is an illustrative frequency trimming result where the thermal power and / or time increases over a series of heating pulse iterations until the room temperature frequency falls within an acceptable range centered around the target frequency. [Figure 36]This example demonstrates a frequency trimming result where the heating power is reduced after three iterations to increase the resonant frequency after initially overshooting the frequency trim target, utilizing the invertible characteristics of temperature-initiated frequency tuning. [Figure 37A] In this particular example, we show a disk ring gyroscope, which is a MEMS structure, along with the two vibration modes of interest, Mode 1 and Mode 2. [Figure 37B] Figure 37A shows an array of electrodes surrounding the MEMS structure, which is used not only in potential normal device operation but also in capacitively coupled Joule heating. [Figure 37C] Figure 37A shows a high-frequency (RF) input applied to a subset of electrodes to preferentially tune the Mode 1 frequency of the MEMS structure, causing the MEMS structure to be heated non-uniformly. [Figure 37D] Figure 37A shows RF inputs applied to different subsets of electrodes to selectively adjust the frequency of Mode 2 in the MEMS structure and obtain a desirable frequency relationship between the two modes. [Figure 38] This demonstrates the modulation of frequency relationships between two modes of a similar MEMS structure based on the activation of a subset of heating terminals, except that Joule heating is achieved through terminals directly coupled to the structure, thus allowing for the possibility of DC heating currents. [Modes for carrying out the invention]

[0005] Detailed explanation In various embodiments herein, temperature-stable, wear-resistant resonators are disclosed, formed from a material laminate having one or more degenerate-doped silicon layers and piezoelectric material layers. In some implementations, the piezoelectric material layer ("piezoelectric layer") is sandwiched between a degenerate-doped single-crystal silicon "core" layer and a degenerate-doped polycrystalline layer, in which case the outer silicon layer functions as an electrode for conducting drive / sensor signals between itself and the piezoelectric layer, thereby preventing the conventional metal electrode layer and its undesirable aging characteristics (e.g., wear-hardening over time). Furthermore, as will be described in more detail later, the layer thickness ratio, (at least) the crystal orientation of the single crystal layer, mode shaping, and / or the concentration / type of the degenerate dopant may, as a whole, be engineered to substantially zero out or nullify the temperature coefficient of frequency (TCF) of at least the first (linear) and second (parabolic) order in the material laminate, in which case the inherent parabolic TCF of the piezoelectric layer is substantially neutralized, for example, by an engineered opposite-polarity parabolic TCF within the degenerate-doped single-crystal silicon layer. Thus, in addition to serving a dual purpose as both a sensing / driving electrode and a resonator bulk layer, the degenerate-doped single-crystal silicon layer provides an engineered "knob" for resulting in a resonant MEMS structure with a temperature-stable resonant frequency (e.g., a combination of zero or near-zero TCF) over a desired operating temperature range (e.g., -40°C to +85°C). Similarly, the degenerate-doped polysilicon layer can function as an abrasion-resistant electrode (and therefore, together with the piezoelectric layer, can be considered as part of a sensing / driving component) and can also enable multiple degrees of TCF engineering design.In further embodiments, one or more in-situ temperature sensing elements are provided (implemented, for example, within the resonator package, within the encapsulation chamber, or optionally within the resonator structure itself) to enable temperature-controlled frequency pull and / or post-resonator output frequency adjustment in order to flatten the net resonator TCF (i.e., the sum of the 1st, 2nd, ..., nth order TCFs), and / or to compensate for the effects of aging, or, in some cases, to allow for runtime frequency adjustment (for example, by enabling closed-loop heating to a desired operating temperature that affects the 0th order TCF). These and other features and embodiments will be described in further detail below.

[0006] Figures 1A–1C illustrate various physical, electrical, and TCF engineering designs of an exemplary piezoelectric MEMS resonator 100 having at least two degenerate-doped silicon layers, referred to herein as a “dual silicon” resonator. Referring first to Figure 1A, the physical lamination of materials shown in section A–A' comprises a degenerately-doped (DD) single-crystal silicon (SC-Si) core, a piezoelectric layer (dielectric), and a degenerately-doped polycrystalline silicon (DD-Poly) layer. The dopant concentration in the outer silicon layer is set to achieve low-loss conductivity and, as a result, allow the silicon layer to function as an electrode for establishing a time-varying piezoelectric operating voltage across the piezoelectric layer, thereby avoiding conventional metal layers that tend to harden over time and shift the resonator frequency in an undesirable manner (e.g., 1E18 atoms / cm³). 3 , 1E19 atoms / cm3, 1E20 atoms / cm 3 , 2E20 atoms / cm 3Sufficiently high (or perhaps even higher). In the particular embodiment shown, the upper and lower electrodes (the structure may be inverted or otherwise reoriented during deployment or use, so "upper" and "lower" refer arbitrarily to the orientation in the drawing) mounted by poly and single-crystal silicon layers respectively, transmit a piezoelectric "drive" signal (V sustain In order to enable the reception of the resonator and to notify the mechanical movement of the resonant structure of the piezoelectric output signal (V sense To enable external detection of the external package, it is electrically coupled to the external package contacts via a mechanical tether and anchoring structure. As shown in the figure, the resonator material laminate can be electrically modeled by plate capacitance (piezoelectric layer) coupled to the drive and sense nodes via a low-loss conductive path.

[0007] Figure 1B shows a more detailed illustrative cross-section of a dual silicon resonator through the anchor, tether, and body. As shown, the piezoelectric layer is implemented through the tether and anchor by an extended aluminum nitride (AlN) thin film, along with two degenerate doped silicon layers. Although shown as uncoupled elements, the tether, anchor, and resonator body are physically coupled to each other, in which case the tether functions as a spring-like structure to allow the mechanical movement of the resonator ("movable micromachined component") which would otherwise be freed from and suspended in relation to the surrounding field area and the underlying substrate or insulating layer (alternatively, or in addition to this, the anchor and one or more tethering structures may be disposed below the resonator body). Therefore, conductive paths can be formed through anchors and tethers to generate electrostatic potentials across the aluminum nitride piezoelectric layer, and thereby activate a resonator, thereby generating its oscillating mechanical motion in one or more mechanical resonant modes (e.g., stretch, breath, lame, deflect, bulk-acoustic, or any other feasible MEMS resonant modes—such as in-plane or out-of-plane). For example, and without limitation, zinc oxide (ZnO), lead zirconate titanate (Pb[Zrx Ti 1-x Various alternative materials, including 100O3 (0≦x≦1), lithium niobate (LiNbO3), gallium nitride (GaN), indium nitride (InN), scandium aluminum nitride (ScAlN), and quartz (SiO4), may be used to mount the piezoelectric layer in the embodiment shown in Figure 1B and in all other embodiments disclosed herein.

[0008] In relation to the engineering design of TCFs, degenerate-doped single-crystal silicon incorporates at least two degrees of authority / control within a single layer: crystal orientation and dopant concentration. Further authority is available in relation to the deposition of piezoelectric thin films on highly doped single-crystal silicon. Specifically, the ratio of the thicknesses ("x / y") of the degenerate-doped single-crystal silicon layer to the aluminum nitride piezoelectric layer can be selected to produce substantially matched, but oppositely signed, secondary TCFs within these two layers, thereby neutralizing or substantially attenuating their combined parabolic contribution to the net resonator TCF, and also providing some degree of control (authority) over the tertiary resonant TCF. Furthermore, a suitable crystal orientation within the polysilicon thin film can also influence the primary and secondary TCFs. Accordingly, as shown in Figure 1C, the first and second TCFs of the dual silicon piezoelectric resonator in Figures 1A and 1B can be engineered (controlled, manipulated) by varying the crystal orientation, dopant type and thickness of the degenerate doped single-crystal silicon layer at a particular doping concentration, the thickness of the aluminum nitride layer, and / or the thickness of the degenerate doped polysilicon layer at a particular dopant concentration. In some embodiments, various TCF levels are engineered to yield substantially zero net TCF (e.g., frequencies within 50 ppm, 20 ppm, 10 ppm, or less of the target) over a desired operating range (e.g., -40°C to 85°C). More generally, a resonator with such multi-order compensation (i.e., nullification of not only the first-order TCF but also the second, and possibly the third and even higher-order TCF terms) can be engineered. • Nullify the first, second, third, and fourth TCF terms, or any two of them, or otherwise attenuate them (for example, to zero, substantially zero, or other negligible levels). • Partially or entirely compensates (or disables or cancels) the third-order TCF, and thereby provides a specially selected non-zero value of the linear TCF to reduce absolute frequency variation over a specific temperature range. • Also called the "turnover temperature," it exhibits one or more local extrema at a temperature-dependent frequency (i.e., a temperature at which a local minimum or maximum frequency occurs). • Shows turnover at the nominal operating temperature. It may be engineered in such a way.

[0009] Furthermore, as a departure from TCF compensation schemes that cumulatively apply material layers (such as one or more material layers to compensate for primary TCFs and one or more other material layers to compensate for secondary TCFs) to compensate for individual TCF terms, the temperature-engineered resonant structures disclosed herein include semiconductor layers or regions engineered to compensate for both linear TCFs and one or more higher-order TCFs themselves, and thereby enable the construction of a “short stack” MEMS resonator composed of a reduced number of material layers in relation to layer / TCF packaging. In one example, the linear TCF of a resonator fabricated from an anisotropic degenerately doped semiconductor (DDS), such as single-crystal silicon, is tuned by rotating the orientation of the resonator shape in relation to the underlying crystal axis. As a second example utilizing anisotropic degenerately doped semiconductors, the linear TCF of a resonator is tuned by changing the shape and / or mode shape of the resonator. As another example, in some embodiments, the semiconductor material is doped to such a high concentration that the polarity (i.e., the sign of the secondary TCF) of the resonator constructed from that material is reversed in relation to the secondary TCF of a resonator constructed from a lower-concentration doped version of that semiconductor (for example, resulting in a positive secondary TCF as opposed to a negative secondary TCF exhibited at relatively low dopant concentrations). The reverse-polarity secondary TCF may be utilized to partially or completely neutralize the secondary TCF of one or more other materials (e.g., a piezoelectric material having the opposite secondary TCF polarity to that of the degenerate-doped semiconductor material) in a composite resonator embodiment over a given temperature range, thereby producing a resonator with a reduced secondary TCF magnitude. As described, resonant structures with engineered linear and higher-order TCFs can be fabricated solely from degenerate-doped semiconductors, or degenerate-doped semiconductors may be deployed within a composite resonant structure to enable engineered temperature stability.For example, composite structures suitable for piezoelectric micromechanical resonators are disclosed below, which address the problems of frequency stability with temperature and the engineering design of linear and higher-order TCFs. As described, such composite structures offer high-quality coefficients, low hysteresis with temperature, low frequency aging with time, compatibility with batch microfabrication methods, small form factor, low sensitivity to shock and vibration, and other desirable features.

[0010] The resonant structures described herein can be fabricated, whole or in part, from or using combinations of degenerate-doped single-crystal or polycrystalline semiconductors (such as silicon, germanium, diamond, carbon, silicon carbide, silicon-germanium, and other compound semiconductors). Pure and low-doped semiconductors are insulating materials at low temperatures. When a semiconductor is doped with certain impurity atoms exceeding a certain dopant concentration, the semiconductor exhibits metallic or highly conductive behavior even at low temperatures (such as in single-crystal silicon near 0 Kelvin). Such semiconductors are described as "degenerate-doped." For example, in single-crystal silicon, this is 4E18 atoms / cm³. 3 This can occur at the phosphorus doping levels mentioned above. More generally, the onset of degeneracy varies with the semiconductor and the dopant. In addition to changes in conductivity, various material properties of the semiconductor change not only with the doping level but also with the temperature dependence of these various material properties. In particular, resonators fabricated with degenerate-doped semiconductors can exhibit significantly different TCFs than similar resonators constructed with versions of semiconductor materials with relatively low doping concentrations. In some cases, it is even possible to reverse the sign (or polarity) of one or more TCFs by changing the doping level of the semiconductor used as a structural material within the resonator. These changes in temperature dependence have been utilized in some resonator embodiments to enable sophisticated engineering design of targeted temperature coefficients.

[0011] In certain embodiments of the resonator composite structures disclosed herein, two of the constituent materials are a degenerate doped semiconductor (DDS) and a piezoelectric material. An example of a DDS resonator, this composite structure can be engineered to simultaneously achieve target values ​​or ranges of values ​​for two or more TCFs of a particular resonant mode. In one embodiment, for example, the composite structure is constructed from degenerate doped silicon (a semiconductor) and aluminum nitride (a piezoelectric material—as described above, other materials may be used), and is engineered such that the primary and secondary TCFs (i.e., linear and secondary TCFs, respectively) of a particular resonant mode of the overall structure are both within a specified tolerance from zero, thereby obtaining a temperature-insensitive or temperature-compensated resonator.

[0012] In addition to the two main constituent materials, further materials may be present within the composite structure. In particular, other conductive materials (which may also be degenerate-doped), such as metal or another semiconductor layer, may be included to function as additional electrodes (as described later, the DDS layer can function as another electrode within the composite structure). Examples of suitable electrode materials, however, include, without limitation, highly doped silicon, silide, tungsten, molybdenum, titanium, or aluminum. The term electrode is used herein, without limitation, to mean a conductive material used to establish an electric field for the conversion of electrical energy to mechanical energy or mechanical energy to electrical energy. It should also be noted that layers applied as electrodes may also function for other purposes, such as piezoelectric or heating functions, for example, and without limitation.

[0013] The embodiments disclosed in the present specification address many or all of the aforementioned problems and challenges in resonator performance through engineering design of multiple parameters or design degrees of freedom of a structure having reduced sensitivity to temperature, while providing several structural advantages including piezoelectric coupling, high quality factor, low hysteresis, low aging, compatibility with batch microfabrication, small form factor, and insensitivity to shock and vibration.

[0014] In the case of mechanical resonators, the natural frequency is primarily determined by the mass density and stiffness of the material from which the resonator is constructed. Changes in material stiffness resulting from changes in ambient temperature are a major concern in resonator design and manufacturing, because this causes the natural frequency of the resonator to change. Changes in material shape resulting from thermal expansion or contraction are also a concern, because this also causes the natural frequency of the resonator to change.

[0015] For illustrative purposes, this may exemplify the principles of TCF engineering design by examining a simple model. One such model is the case where the resonator structure is constructed from thin layers and only material movement along a single axis is considered. In this simple example, the stiffness of the material is described by a single numerical value, the effective elastic modulus. This is a simplification of the physical case where all dimensions of movement need to be considered and the stiffness of the material can be described by a tensor. In this simple model, the elastic modulus of an anisotropic material depends on the orientation of the material.

[0016] In the case of composite structures, a simple model for the nth-order temperature coefficient of frequency is the weighted average of the contributions of all components of the resonator. This average value can be described as follows for the case of a laminate of thin material films (or layers):

Formula

number

number

number

[0017] Equation (2) shows that the first requirement for engineering the frequency-temperature coefficient of a resonator using composite materials is to use materials that have the desired value in a single unit. For example, λ n If it is desirable that it be zero, then at least one

number

number

[0018] Also, equation (2) is,

number

number

[0019] Despite the conventional emphasis on linear TCF control, analysis shows that composite resonator performance can be significantly enhanced through control of at least the first two temperature coefficients. As described above, resonator implementations with control of at least the first two frequency temperature coefficients can be constructed from aluminum nitride and degenerate doped single-crystal silicon. Such resonators can be compatible with piezoelectric conversion and, without limitation, can have other advantageous properties, including a high quality factor (Q), low hysteresis with temperature, low frequency aging with time, compatibility with batch microfabrication, small form factor, and insensitivity to shock and vibration.

[0020] In addition to controlling at least the primary and secondary TCFs, the following, but not exhaustive, list of criteria apply when designing the selected resonator embodiments disclosed herein. The target frequency temperature coefficient of the overall structure is obtained by combining the temperature coefficients of the individual materials. For example, if the target primary TCF is zero or near zero, and the primary TCF of at least one component material is substantially positive, then the industrial design and / or selection of at least one other component material is such that the primary TCF is negative. There are N design parameters to enable control over N temperature coefficients. • The combination of design parameters has sufficient design authority to enable solutions within the design space defined by manufacturing constraints and design constraints.

[0021] Aluminum nitride resonators typically have a negative linear and second-order TCF. The temperature coefficient of thin-film polycrystalline aluminum nitride has little dependence on the thin-film structure. Similarly, resonators constructed from non-degenerate single-crystal silicon have a negative linear and second-order TCF, and the TCF tends to have little dependence on the crystal orientation.

[0022] The linear TCF of a resonator constructed from degenerate-doped single-crystal silicon can be positive or negative, depending on the crystal orientation, doping level, and mode shape. Therefore, the crystal orientation constitutes a design parameter (or degree of design freedom) that can be tuned to control the linear TCF term. The secondary TCF of a resonator constructed from degenerate-doped single-crystal silicon can be positive or negative, depending on the dopant concentration, crystal orientation, doping level, and mode shape. Figure 2A shows examples of such positive / negative primary and secondary TCFs, as well as positive and negative zero-order TCFs (i.e., temperature-independent frequency offsets).

[0023] For example, by manipulating orthogonal design parameters such as crystal orientation and dopant concentration, it becomes possible to independently tune (i.e., control and potentially nullify) both the first-order and second-order (linear and second-order) TCF characteristics of a degenerate-doped single-crystal silicon layer. Furthermore, while polycrystalline silicon resonators can be degenerate-doped to achieve linear and second-order ranges, one degree of design freedom may be lost if the material lacks a principal crystal orientation.

[0024] Figures 2B to 2E show an exemplary embodiment of a DDS resonator, along with an optional electrode arrangement within and adjacent to the resonator structure, and a plan view of the resonator shown in Figure 1a.

[0025] First, referring to Figure 2B, a resonant structure comprising at least one degenerate doped semiconductor layer ("DDS resonator") is arranged between two electrode structures (used, for example, to drive and sense the resonator) and having one or more anchor points. In the illustrated embodiment, a spring-like member or "tether" extends from the opposite side of the resonator body to the anchor within the surrounding material field to establish dual anchor points, but in alternative embodiments, more or fewer anchor points may be implemented. Also, although a rectangular or rectangular resonator shape is illustrated, the DDS resonator can be manufactured in any feasible shape and / or aspect ratio.

[0026] The electrodes on both sides of the DDS resonator are shown with dashed outlines to emphasize their optional characteristics (this notation also applies to other drawings in this specification, but the absence of dashed outlines should not be interpreted as meaning that a given element or structure is essential). Furthermore, one or more electrically insulated electrode regions may be implemented within a given resonator layer, as indicated by T-shaped regions outlined within the resonator body. In alternative embodiments, one or more alternatingly shaped (i.e., different shapes from those shown) electrode regions may be used, and the resonator body itself may be used as an electrode.

[0027] In the case of a single-layer degenerate doped silicon resonator, the resonator's motion can be detected electrostatically or piezoelectrically by appropriate electrical connections. Figures 2C to 2E show cross-sections of exemplary material laminates (i.e., crossing the resonant structure along line A-A' in Figure 2B), including a monolithic (single-layer) laminate in Figure 2C, a two-layer material laminate in Figure 2D, and a three-layer material laminate in Figure 2E. As will be discussed later, in alternative embodiments, further material laminates and / or laminates of materials different from those shown in Figures 2C to 2E may be present. As described above, since a single layer of uniform degenerate doped silicon has at least two design parameters (crystal orientation and dopant concentration), a single-layer resonator composed of uniform degenerate doped single-crystal silicon (Figure 2C) can be industrially designed to have zero or near-zero primary and secondary TCFs through a combination of manufacturing processes and design. Furthermore, the dopant concentration does not need to be uniform. As a result, a number of arbitrary design parameters (i.e., "knobs" or degrees of freedom for manipulating resonator performance throughout the design) are permitted. Furthermore, it may be advantageous to create one or more regions inside or on top of the resonator with different dopant concentrations and / or different dopants, as shown by the varying degrees of shading in Figure 2F. Also, as shown in Figure 2G, regions inside or on top of the resonator may be created to have locally deposited or patterned layers of material with desirable properties. For example, it may be advantageous to place these regions within high-stress areas in the vibration mode geometry of the resonator, thereby enabling control over first, second, third, or even higher-order TCF values.

[0028] Furthermore, resonators can be industrially designed to have non-zero, but controllable, primary and secondary TCFs to achieve specific design intents. For example, the primary TCF can be designed so that the total frequency variation with temperature is minimized by compensating for third and other odd-order higher-order TCFs. As another example, the primary TCF can be designed to regulate the temperature at which the frequency change in relation to temperature reaches an inflection point, local minimum, or local maximum. The temperature at which the resonator reaches a local minimum or maximum frequency is generally referred to as the turnover temperature. Also, the resonator TCF may be designed to disable TCFs associated with its maintenance circuit (i.e., a circuit that maintains the mechanical movement of the resonator) or oscillator system. As a final example, the primary and secondary coefficients can be selected to be relatively insensitive to angle and dopant concentration for the purpose of improved manufacturability. Figure 2H shows an example of such an industrially designed TCF.

[0029] Referring again to Figure 2D, a two-layer resonator can be constructed consisting of degenerate doped silicon and a further thin film. When the silicon layer is a single crystal, this structure has at least three design parameters: the crystal orientation and dopant concentration as described above, and in addition, the ratio of the silicon thickness to the thickness of the added thin film. Thus, a two-layer resonator consisting of degenerate doped silicon and a further thin film can have the ability to control three TCFs. In some embodiments, including that shown in Figure 1C, the further thin film is a piezoelectric material (e.g., aluminum nitride), but the further thin film (or other material layer) may instead be any semiconductor, insulator, or metallic material selected for its TCF coefficient or other desired mechanical or electrical properties.

[0030] In addition, a three-layer resonator can be formed, as shown in Figure 2E (i.e., with or without the electrically insulated electrode region described). In one embodiment, such a three-layer resonator includes a degenerate doped single-crystal silicon layer coated within aluminum nitride (for forming the piezoelectric layer) and a further conductive layer (e.g., a metal layer or another degenerate doped polysilicon electrode layer). As described above with reference to Figure 2C, the primary and secondary TCFs can be controlled by varying the crystal orientation of the lower (single-crystal) silicon at specific doping levels and thicknesses, the thickness of the aluminum nitride, and the thickness of the polysilicon at specific dopant concentrations. A suitable crystal orientation within the polysilicon thin film can also affect the primary and secondary TCFs. It is possible to select a set of alternative design parameters to industrially design the TCF of the thin-film laminate, and the previous examples are only one of many possibilities. In addition, as shown in Figure 21, one of the layers in the three-layer resonator can be made thin enough so that its contribution to the composite structure's TCF is minimized (e.g., negligible or otherwise attenuated) and the compensation problem is reduced to that of the two-layer resonator case. For example, the top layer can be implemented by a thin conductive metal or semiconductor layer instead of a degenerate doped polysilicon electrode layer.

[0031] Further layers can be added to the laminate. An example shown in Figure 2J includes degenerate doped single-crystal silicon with aluminum nitride sandwiched between the upper and lower electrodes. The electrodes can be fabricated from any conductive metal or semiconductor thin film, such as polysilicon, aluminum, molybdenum, titanium, tungsten, or silicides formed using metal and silicon.

[0032] In various embodiments, a single MEMS system 200 may include multiple elements fabricated together on the same substrate as the DDS resonator. Referring to Figure 3, for example, the MEMS system 200 may include a DDS resonant element 201 (i.e., a form of MEMS resonator), one or more temperature sensing elements 203 ("temperature sensors"), and one or more heating elements 205 ("heaters"). The temperature sensing elements may be used as part of an active temperature compensation system. An example of a temperature sensing element is a thermistor, which has a temperature-dependent electrical resistance. Heaters may be included for initial calibration of the resonator frequency stability or to maintain the MEMS system at a nearly constant temperature despite fluctuations in ambient temperature. Optionally, the temperature sensors and / or heaters may be excluded from the MEMS system 200. As described above (and will be discussed in more detail later), the resonator structure may be used as a sensor instead of a frequency reference. Examples of alternative resonator applications include filters, gyroscopes, accelerometers, pressure sensors, microphones, magnetometers, and mass sensors.

[0033] The DDS resonators described herein may be deployed with or without complementary temperature compensation, thereby realizing a purely passive temperature compensation scheme or, for example, a combination of passive and active temperature compensation. Active electrical compensation circuits, by definition, increase the power consumption of the system, but a combination of passive and active compensation (e.g., a DDS resonator in combination with an active compensation circuit) can enable the realization of stability targets with less power than active compensation alone, or greater stability than that achievable by either scheme alone. Passive mechanical temperature compensation is possible through material selection and structural design in both monolithic and composite resonator structures.

[0034] The DDS resonators disclosed herein may be combined with further elements to form a system having improved temperature stability and / or other useful functions. In Figure 4A, for example, the DDS resonator 301 is combined with a maintenance circuit 303 to form an oscillator. The resonant frequency of the oscillator may be modified in a temperature-dependent manner (i.e., as shown in Figure 4A, a temperature signal from the sensor 305 is received in the frequency-changing element 307, which then provides a temperature-dependent resonant frequency control signal to the DDS resonator 301 and / or the maintenance circuit 303) to result in a resonant frequency with improved temperature stability compared to that achievable by the DDS resonator alone. For example, a temperature-dependent electrostatic field may be applied directly to the DDS resonator by using a control electrode manufactured together with the resonator. Figure 4B shows an example of this method, in which the electrodes are formed by the degenerate doped silicon (DDSi) layer (electrode 2) and conductive layer (electrode 1) of the three-layer resonator embodiment described above (i.e., having DDSi, AlN, and a conductive layer, although in alternative embodiments other resonator structures / materials may be used), and a temperature-dependent electrostatic field is formed by the time-varying and temperature-dependent difference Ve1-Ve2 between the potentials of the two electrodes.

[0035] As another example, if one component of the resonator has a large piezoelectric response, the mechanical stress on the resonator can be changed in a temperature-dependent manner to adjust the resonator frequency. Figure 4C shows an example of such a configuration in the environment of the three-layer DDSi / AlN / conductive material resonator described above, but other resonator structures and / or materials may be used.

[0036] For example, in another embodiment shown in Figure 4D, a capacitive element may be included in the resonator maintenance circuit 321, and its capacitance can be changed in a temperature-dependent manner, thereby realizing a variable capacitance element 323 (i.e., a system including the DDS resonator 301 and the maintenance circuit 321) that can be used, for example, to tune the frequency of the oscillator system.

[0037] In one alternative embodiment shown in Figure 4E, the resonant frequency of the DDS resonator 301 is modified by a frequency-changing element 331 within the resonator system after being output from an oscillator (at least partially formed by the DDS resonator 301 and the maintenance circuit 303, as shown). For example, in a more specific implementation shown in Figure 4F, a temperature-dependent signal (e.g., from a temperature sensor shown in 305 in Figure 4E) can be provided to a fractional-N phase-locked loop (an example of a frequency-changing element) to generate an output frequency that is significantly more stable with temperature than in the case of a resonator alone.

[0038] As shown in Figure 4G, any of the oscillator systems shown in Figures 4A to 4F (or other oscillator systems utilizing DDS resonators) may include a programmable / storage circuit 350 in which TCF coefficients, control settings, or other information can be stored internally. The TCF coefficients recorded or stored within such an oscillator system may be based on the characteristics of individual resonators (301) or groups of resonators. In addition, the coefficients may be based on the characteristics of individual maintenance circuits (303) or groups of maintenance circuits. For example, the TCF behavior of an oscillator or resonator can be determined by sweeping the temperature and recording the frequency, as shown in 355, or by measuring room temperature characteristics (e.g., resistivity and frequency) that predict time-dependent behavior.

[0039] A programmable / storage circuit capable of storing the TCF coefficient or other parameters indicating temperature-dependent behavior may include, for example and without limitation, registers, or any other implementable on-chip or off-chip memory elements, such as one-time-programmable (OTP) memory, electrically programmable read-only memory (EPROM), flash memory, and other volatile or non-volatile memory elements.

[0040] Furthermore, the TCF coefficient, or other parameters indicating temperature-dependent behavior, may be stored as resistance values. As shown in Figure 4H, for example, a MEMS resonator die may include at least one resistor whose resistance value can be trimmed by a laser (or other method such as thermal melting) to record values ​​related to the device's behavior with temperature. Thermistors and / or heaters may also be used to store information in this manner. For example, using a thermistor or heater for this purpose avoids further bonding pads or electrical interconnections.

[0041] The stored temperature behavior information may be used by the oscillator system to improve its frequency stability. The system can read the stored information, combine it with temperature measurements, and apply corrections to the resonator or oscillator system frequency. This operation is shown, for example, in the embodiment of Figure 4I, in which the frequency changing element 375 receives a temperature signal from the sensor 305 and reads temperature-based correction data ("data") from the programmable storage 350. A frequency correction signal corresponding to the correction data is then output to the resonator, the maintenance circuit, and / or the output conditioning circuit (e.g., the PLL described above with reference to Figure 4F).

[0042] Figure 5A shows one embodiment of a MEMS configuration having a DDS resonator 401 integrated with one or more components of an active temperature compensation system. The DDS resonator may be implemented according to any of the resonator embodiments described herein and comprises one or more layers (or other depositions or configurations) of degenerate doped semiconductor material. In the illustrated embodiment, the temperature compensation circuit comprises one or more temperature sensing elements 403 (e.g., thermistors or other temperature sensors), one or more heating elements 405, and a temperature control circuit 407 for controlling the operation of the heating elements (e.g., supplying power to the heating elements as required to reach a predetermined or programmed temperature setpoint or temperature range). Figure 5B shows an example of this temperature compensation operation, showing a time-varying heater output generated according to the time-varying ambient temperature to maintain a constant or nearly constant resonator temperature.

[0043] As shown in Figure 5A, the integration of the DDS resonator and temperature compensation system components can vary from implementation to implementation. For example, in one embodiment shown in shaded region 411, the DDS resonator 401 is integrated with the temperature sensor 403 ("Integrated T-Sense") (i.e., manufactured together or otherwise formed on the same substrate or die), while the temperature control circuit 407 and heater 405 (i.e., one or more heating elements) are mounted outside the die. In another embodiment shown by region 415, the temperature control circuit 407 and heater 405 are integrated with the temperature sensor 403 and DDS resonator 401, thereby establishing a fully integrated active temperature compensation system within the MEMS resonator die. Although not specifically shown, instead, the DDS resonator 401 may be integrated with the heater 405, while one or more temperature sensors and / or temperature control circuits remain outside the die.

[0044] In some embodiments, the temperature sensors shown in Figures 4A and 4E may be mounted within one or more component members of the encapsulated dual silicon resonator, or within a multi-die package including a dual silicon resonator (MEMS) die and a logic die. Figure 6 illustrates various options for such temperature sensor integration, including temperature sensor mounting within the lid or device layer of the encapsulated dual silicon resonator, and / or within a co-located logic die that further houses a maintenance / sensing circuit for driving the dual silicon resonator into one or more resonant oscillation modes and for detecting the resonant mechanical motion of the resonator. In the case of in-situ placement within the device layer of the encapsulated resonator structure, the temperature sensor may be mounted by a second micromachined structure—more specifically, by a micromachined (or MEMS) thermistor structure having any number of shapes (and therefore limited mechanically induced nonlinearity of the temperature dependence of the end-to-end thermistor resistance) that are substantially free from the device layer substrate and allow for thermal expansion and contraction that are relatively stress-free / strain-free. Although not specifically illustrated, the end terminals of the MEMS thermistor may be coupled to a TSV within the encapsulation structure (lid and / or substrate) and ultimately to a package-level contact to enable a temperature sensing output signal. When mounted within a lid wafer or logic die, the temperature sensor may be implemented by silicon, polysilicon, or metal thermistor functionality, a pn junction, and / or other thermally sensitive functionality. In further embodiments, which will be described in more detail below, the temperature sensor may be implemented by patterned traces and / or pn junctions within one or more layers of the dual silicon resonator itself.

[0045] Figure 7 illustrates an exemplary process for manufacturing a MEMS thermistor and a dual-silicon MEMS resonator (having the two degenerate-doped silicon layers and piezoelectric layer described above) within adjacent regions of the same SOI substrate (i.e., within the same encapsulated device layer). As shown, an oxide layer is deposited on the SOI substrate and then etched (e.g., wet-etched) to yield a masked thermistor region. Following PSG deposition (e.g., via gas-phase POCI3) and mini-drive cycles (relatively short-duration drives) to achieve relatively shallow dopant diffusion, a longer annealing (relatively long and / or high-temperature drives) is then performed to achieve a deeper final dopant diffusion profile. At this point, the single-crystal silicon device layer is degenerate-doped (with a process-dependent gradient), except for the thermistor region below the oxide mask, which remains relatively undoped. The remaining layers of the dual silicon resonator (e.g., AlN and ISDP, or any other material by the above-mentioned deformation) are deposited, the oxide mask is removed, and a trenching / etching and release process is performed to complete the two together-positioned MEMS elements—the dual silicon resonator and the adjacent MEMS thermistor. By juxtaposing the MEMS thermistor and dual silicon resonator within the same apparatus layer and within the same (ultimately) encapsulated chamber and singularized die, the temperature gradient between the thermistor and resonator, which is problematic in relatively non-proximity temperature sensing / resonator configurations, is eliminated (or made negligible), thereby improving the accuracy of the various temperature compensation schemes shown in Figures 4A and 4E.

[0046] Figure 8 shows an illustrative interconnection configuration within a dual silicon resonator having an additional low-doped (or undoped) single-crystal silicon thermistor layer as part of the resonator structure. This configuration adds a layer to the resonator material laminate (in this case, the thermistor layer is positioned below the dual degenerate-doped silicon layer and piezoelectric layer described above—any other laminate location is possible), but the thermal coupling of the thermistor layer to the rest of the resonator material laminate ensures a zero or near-zero temperature difference between these two resonator regions, thereby avoiding the error-inducing temperature gradients that are problematic in configurations that are not relatively close together. As shown, an additional pair of sensing terminals may be coupled across the thermistor layer (e.g., through a conductive structure in a tethering / mooring structure to the opposite lateral end of the thermistor layer) and routed to the external contacts of the encapsulated material laminate and the final resonator / thermistor package.

[0047] Figure 9A shows an embodiment of a DDS resonator 500 having some of the features described above. More specifically, the DDS resonator 500 may be a single-layer structure (i.e., composed only of a single degenerate-doped semiconductor such as degenerate-doped silicon), or it may be a multilayer structure having, for example, an aluminum nitride (AlN) or other piezoelectric layer disposed between the degenerate-doped silicon layer and the conductive layer shown in Figures 1A to 1C. Furthermore, the dopant type or concentration in the DDS layer or any other layer of the resonator 500 may be non-uniform (for example, the concentration may be relatively high or low in the high-stress area 501 or other areas of the resonator body), and the resonator may be manufactured such that the resonator axis 503 is positioned at a non-zero angle φ (i.e., "resonator angle") in relation to the crystal axis 504. As described above, the resonator angle, DDS dopant concentration, and type (including any non-uniformity) may be specially industrially designed to nullify the first and at least one higher-order frequency temperature coefficients, respectively. The mode shape, relative layer thickness, and dopant type / concentration of other layers (e.g., conductive layers formed from degenerate-doped polysilicon) may also be specially selected in combination with the dopant concentration / type of the bulk DDS layer to produce a desired temperature-dependent resonant behavior, such as temperature-sensitive or temperature-stable (or temperature-insensitive) behavior, over one or more desired operating temperature ranges. In the particular example shown, the DDS resonator 500 has an elliptical shape with a transverse dimension (i.e., perpendicular to the resonator axis 503) narrowed between the spring bearing anchors 507a and 507b. Trench 512 is etched or otherwise formed around and / or below the resonator and anchor spring elements in order to free the DDS resonator and anchor spring elements from the substrate field area 510 (i.e., to free these elements to move in relation to it).

[0048] The DDS resonator 500 may have a cross-section AA schematically shown in Figure 1B—that is, a degenerate-doped (DD) single-crystal silicon layer, an aluminum nitride piezoelectric layer, and a degenerate-doped polysilicon electrode layer. Spring elements ("springs") and field area anchors are provided on both sides of the resonator body to form the individual anchors shown in 507a and 507b of Figure 9A. In alternative embodiments, including single-anchor configurations or configurations with more than two anchors, various other mooring configurations with or without spring mounts may be utilized.

[0049] Figure 9B shows an illustrative finite element model of the DDS resonator in Figure 9A, illustrating the displacement and stress distribution during resonant oscillation (or oscillation). For example, the vectors (arrows) protruding from the edges of the resonator body indicate the direction of the resonator's motion during the expansion phase of the oscillation cycle. In the illustrated example, high-stress areas occur between the anchors, low-stress areas occur at the opposite end of the resonator axis (i.e., the axis shown in Figure 9A), and stress contour lines occur between the low-stress and high-stress areas. The stress within the anchors is approximately zero.

[0050] Figures 10A to 10I show, but not exhaustive, examples of alternative resonator shapes / designs with each exemplary resonator implemented in the

[0110] crystal orientation (i.e., an axis 45 degrees off from the single-crystal silicon layer axis and / or the principal axis of the polysilicon layer, although various other angular orientations can be selected according to the purpose of TCF industrial design). First, referring to the resonator shown in Figure 10A, tethers (springs) positioned in the center on both sides secure the resonator body, which would otherwise be free, to the field area anchor. The increased end mass of the resonator tends to limit (restrict) the interaction of modes outside the desired resonant frequency over the target frequency range.

[0051] Referring to the resonators in Figures 10A to 10I as a whole, the resonant motion generates stress in a selected direction across the resonator body, particularly in the

[0110] axial orientation shown in the illustration, from the perspective of an in-plane anisotropic single-crystal silicon core. Slots or vents (e.g., about 7 microns wide) are provided within the resonant body to provide stress relief, facilitate gas-phase HF emission, and further enable lateral dopant diffusion in at least some processes (as described above with reference to, for example, Figures 2B and 3I to 3K), and / or to realize the industrial design of the TCF. For example, in the resonators of Figures 10B and 10C (and others), the location and size of the slots are selected to enhance dopant concentration in high-stress regions and, conversely, to reduce dopant concentration in low-stress regions. In the resonator designs of Figures 10D, 10E, 10F, and 10G, vents in the field area (outside the resonator body) may be used to release these areas during vapor-phase HF etching, thereby forming a cantilever or other structure that suppresses / avoids field-area interference associated with resonant operation. The illustrative design in Figure 10G includes a single centrally located anchor / tether from which an open vent extends and is tuned to limit the transmission of vibrations to the resonator bulk. Embodiments in Figures 10H and 10I show a centrally anchored resonator having two or more open members (or appendages) extending from it. The resonator in Figure 10H resonates, for example, primarily in extension modes (each point mass moves in-plane relative to the anchor), while the four girder members extending outward from the central anchor in the embodiment of Figure 10I resonate in extension modes (actually acting like tuning forks with identical ends). In alternative embodiments, including those that intentionally exhibit multiple simultaneous resonance modes (for example, having different TCF characteristics as described later), various other resonator core shapes, mooring methods, number of appendages, angular orientations, etc., may be implemented.

[0052] Although omitted in some of the dual silicon resonator embodiments described above, one or more metal layers or silicides may be introduced into such structures to improve electrode conductivity and / or to serve as seedbeds for improving the material structuring of the piezoelectric layer (e.g., growing relatively regular vertical particles in the aluminum nitride piezoelectric layer). Figure 11A shows a configuration with layers such as titanium nitride or molybdenum formed on degenerate doped single-crystal silicon before piezoelectric layer formation, in which case the upper electrode is mounted by a layer of highly doped polysilicon, as before. Figure 11B shows a similar configuration in which metal deposition (e.g., titanium or tungsten) on the degenerate doped single-crystal silicon layer is thermally driven to form a silicide seedbed (e.g., TiSi2 or WSi) for improved piezoelectric layer formation and improved lower electrode conductivity. Although not specifically shown, the layered structure shown in Figure 11A may be rearranged by reversing the positions of the degenerate doped poly layers and metal layers. While such a configuration may be susceptible to aging / work hardening, it can improve the conductivity of the upper electrode without sacrificing the thermal frequency trim oligopoly provided by the degenerate-doped polysilicon layer.

[0053] Figures 12A and 12B show an alternative resonator material laminate having the three layers shown in Figure 1A (i.e., two degenerate-doped silicon layers and one piezoelectric layer) along with an additional metal layer. More specifically, in Figure 12A, the additional metal layer is positioned between the degenerate-doped poly layer and the piezoelectric layer and functions to at least partially improve the conductivity of the upper electrode. In one embodiment, for example, the metal layer functions solely as an upper electrode for the piezoelectric layer (e.g., having a field area via direct contact with the embedded metal layer), in which case the degenerate-doped poly layer can primarily function as an authority for thermal frequency trim. In the embodiment of Figure 12B, the degenerate-doped poly layer is repositioned on the opposite side of the piezoelectric layer (i.e., sandwiched between the piezoelectric layer and the core DD single-crystal silicon layer), thereby improving the conductivity of the lower electrode while maintaining the thermal trim authority of the poly layer. Furthermore, although not specifically illustrated, additional metal layers may be provided adjacent to the lower surface of the piezoelectric layer (i.e., two metal layers sandwich the piezoelectric layer) to minimize conductivity loss without sacrificing the TCF industrial design authority provided by the degenerate-doped single-crystal silicon core layer or the thermal trim authority provided by the degenerate-doped poly layer. Moreover, dual degenerate-doped silicon layers (single-crystal and polycrystalline silicon) are components of all material laminates described herein, but in all cases (including embodiments described later), either or both of these layers may be lightly doped, undoped, or, in some cases, completely omitted. For example, in this case, their contribution to the resonator bulk, TCF industrial design, thermal frequency trim, and / or other industrial design or equipment finish authority is unnecessary.

[0054] As described above, the layer thicknesses within a dual silicon resonator are generally non-uniform and selected to yield desirable TCF characteristics (e.g., the core single-crystal silicon layer is 30 × the width of the aluminum nitride piezoelectric layer), as well as the size, aspect ratio, or other dimensions of the bulk resonator. However, due to their differing surface tensions, the material layers tend to warp when laminated into a composite laminate, which complicates downstream manufacturing steps (and may result in undesirable modal characteristics or, otherwise, degraded runtime performance). Figures 13A and 13B show embodiments of a symmetrical dual silicon material laminate that avoid surface tension imbalances (and the resulting warping). In the embodiment shown in Figure 13A, for example, after manufacturing two dual silicon / piezoelectric layer material laminates as shown overall, one of the material laminates is inverted and bonded to the other to obtain a laminate of six layers (or five layers if the bonded polysilicon layer is considered as a single layer) with a symmetrical line at the bonding surface. Thus, the relatively thick degenerate doped single-crystal silicon core at the bottom of the laminate is balanced by the degenerate doped single-crystal silicon core of the same height ("h1") at the top of the laminate. Electrically, the laminate can be considered to have upper and lower electrodes (formed by comparable degenerate doped single-crystal silicon layers) having a series-connected capacitor (two piezoelectric material layers) bonded to each other through the bonded degenerate doped polysilicon layer, coupled between the respective electrodes—a pair of series-connected capacitors electrically equivalent to a single capacitive element having twice the basic capacitance. One advantage of this method is the relatively high material stack profile obtained as a result of the two single-crystal silicon (core resonator) layers, in addition to the balance of surface tensions. This configuration can satisfy large profile design specifications (e.g., resonator height of 12-20 microns or more) without requiring excessive process scaling or additional material layers.

[0055] Figure 13B shows an alternative symmetric dual silicon material laminate, in which a bondable conductive material layer is formed between the core single-crystal silicon layer and the piezoelectric layer, and then another layer of this type (sandwiching the piezoelectric layer between two thin films of the bondable conductive material) is formed on the piezoelectric layer. After surface preparation (e.g., chemical-mechanical planarization), another core silicon layer is bonded to the material laminate, thereby forming a substantially symmetric material laminate (without the lower insulator and handle wafer) having the same series-coupled capacitor electrical model as the material laminate in Figure 12A. In one variation of the embodiment in Figure 12B, the piezoelectric layer may be sandwiched between non-conductive bonding layers.

[0056] The following are at least some of the advantages that can be achieved by the embodiments disclosed herein. Degenerate-doped silicon can replace two separate materials previously used in piezoelectric resonators: namely, a temperature-compensating material (e.g., SiO2) and a conductive material (e.g., Mo). Degenerate-doped silicon possesses temperature-compensating capabilities and offers sufficiently low electrical resistance values ​​(e.g., 1 to 50 ohms) to function as an electrode material for a wide range of applications. Degenerate-doped single-crystal silicon promotes improved frequency stability with temperature by allowing the deactivation of both primary and secondary TCFs. The doping and orientation of the degenerate-doped silicon layer provide at least two degrees of freedom for deactivating at least two temperature coefficients. The examples described above demonstrate that primary and secondary TCF deactivation of composite piezoelectric resonators using highly doped silicon is possible and within accessible design space. The improvement in temperature coefficients enabled by the disclosed embodiments results in the possibility of frequency fluctuations of less than + / -10 ppm across the industrial temperature range of -40 to +85°C. In contrast, micromechanical resonators with only primary TCF compensation typically exhibit fluctuations of + / -50 to 200 ppm across the industrial temperature range. Removing oxide and metal interfaces improves the mechanical quality factor of the resonator by removing layers that have potentially large acoustic losses and by removing interfaces that can significantly increase the mechanical losses of the resonator. Furthermore, the substitution of metal and oxide layers within the structure with semiconductors eliminates work hardening, fatigue effects, and interface effects that contribute to temperature-dependent frequency hysteresis and time-dependent frequency aging. • Industrially designed resonators with TCF characteristics can be produced from one or more layers of material. Within a single layer, if the material has properties similar to degenerate-doped silicon, the first and second-order TCF coefficients can be neutralized through design and doping. Within a layer having one or more material properties, one or more regions may exist. For example, a single silicon layer may have at least one region containing at least one doping level and at least one dopant. A single material layer may have at least one region containing at least one material type. Each of these regions can add further degrees of freedom to the TCF behavior of the resonator. By adjusting the size and characteristics of these regions, the nominal frequency and the first, second, third, and higher-order TCF terms can be affected.

[0057] Micro-machined structures within micro-electromechanical systems (MEMS) can benefit from in-manufacturing or post-manufacturing heating for a variety of reasons. Conventional in-manufacturing heating in an oven or furnace can be effective when a common temperature needs to be achieved across the entire MEMS wafer or batch of wafers, but new manufacturing and post-manufacturing processes often require iterative heating at precise die-specific or wafer-specific temperatures. In addition, some processes and / or products can benefit from non-uniform (or regional or localized) heating that is not readily achievable by oven treatment of the entire die or wafer.

[0058] In addition to the various temperature-stable and wear-resistant properties described above, the degenerate-doped polysilicon layer and / or degenerate-doped single-crystal silicon layer of the resonator structure may be subjected to thermal cycling treatment via Joule heating or radiant heating techniques to achieve targeted post-encapsulation and / or post-packaging adjustment of the resonator frequency—for example, adjustment of the target output frequency of the natural frequency of a wafer-scale or singulated resonator to 50 ppm, 20 ppm, 10 ppm, or less. More generally, on-die structures that enable heating or overheating of micromachined elements within a MEMS device (i.e., including the resonator structure described above, without limitation) are disclosed in various embodiments below. In the first group of “contact heating” embodiments, ohmic or resistive heating (“Joule heating”) is generated, and in some cases, a DC conduction path is established through the target micromachined structure to enable the target element to be heated to a temperature significantly above the nominal MEMS operating temperature range (i.e., “overheated”). In some contact heating embodiments, a "tether" structure is used in which target micromachined elements are interconnected to individual anchors in order to source and think DC current and, optionally, to provide thermal insulation in relation to the anchors and the apparatus substrate. In other contact heating embodiments, one or more electrode structures formed within the material laminate of the MEMS resonator (or other movable micromachined member) are patterned to generate one or more apparatus heating hot spots.

[0059] In the group of "capacitance-coupled heating" embodiments, an alternating current (AC) flow is generated within the target micromachined element by applying a sufficiently high-frequency signal to adjacent electrodes (i.e., non-movable electrodes that are capacitance-coupled to a movable micromachined component and, in the case of a micromachined resonant component, can function in the operation of the device as a resonator drive electrode and / or resonator sensing electrode). In further embodiments, direct or capacitive coupling to layers separated by individual dielectrics of the micromachined structure is utilized to transport radio frequency (RF) energy across dielectric boundaries and thereby heat the separated layers. In all such embodiments, the MEMS resonator structure or a portion thereof (e.g., one or more layers of a multilayer device) may be patterned to improve or delay the Joule heating effect. Also, in all cases, multiple energy supply ports may be provided to enable localized heating of individual regions and / or layers of the micromachined component. In self-heating embodiments, a programmable steering circuit (for steering AC or DC current to a selected energy supply port or group of ports) and / or a programmable heating control circuit (for establishing a desired heating profile) may be provided on the same die as the target micromachined component or on another die in a multi-die package. In further embodiments, radiant heating (such as laser or radiofrequency heating) may be used to overheat the MEMS resonator structure or a portion thereof, which includes, for example, the transfer of radiant energy through a transparent (i.e., transparent to the relevant wavelength) lid or other structure of the encapsulated or packaged MEMS resonator. These and other embodiments and features are disclosed in further detail below.

[0060] Figure 14 shows an illustrative micromachined component (or structure) in a microelectromechanical system (MEMS) that can be heated or superheated using various techniques and circuit configurations disclosed herein. In the configurations shown below and the embodiments described, the micromachined component is a kinetic resonant component in a MEMS device and includes at least one degenerate doped semiconductor (DDS) layer according to the various embodiments described above. In all cases, the micromachined component may instead be an accelerometer, thermistor, or a kinetic mass in any other useful MEMS structure and may lack a DDS layer. The DDS layer, if present, may be, for example, 1e18 atoms / cm³. 3 , 1e19 atoms / cm 3 , 1e20 atoms / cm 3 , or 2e20 atoms / cm³ 3 DDS may be implemented by doping single-crystal, polycrystalline, and / or amorphous forms of silicon, germanium, etc., with relatively high concentrations of dopants (e.g., arsenic, boron, phosphorus, antimony, etc.). Therefore, “DDS” should be understood to mean not only degenerate-doped silicon, but also various other degenerate-doped semiconductors, including, for example and without limitation, degenerate-doped germanium, 3-5 compounds, silicon-germanium, etc. In this specification, degenerate-doped silicon is referred to in some examples simply because it is the most common semiconductor in industry, and such references should not be considered limiting.

[0061] Referring further to Figure 14, the resonant member is fixed to one or more anchors by individual tethering structures ("tethers") and may be arranged between individual drive / sensor electrodes and / or may have patterned electrodes in its upper or intermediate layer. Detailed Figures 615, 617, and 619 show several possible implementations of the resonant member, including a resonant structure formed entirely from DDS (e.g., degenerate doped silicon), a DDS layer having a layer of piezoelectric material arranged on top thereof, and a piezoelectric layer sandwiched between the DDS layer and the electrode layer. In the latter three-layer implementation, the electrode layer may include one or more conductive electrode regions isolated from each other by a dielectric (illustrated), or integrated electrodes or merged within an electrode layer.

[0062] Figure 15A shows a profile diagram of an exemplary MEMS device having a DDS resonator (an example of a movable micromachined or microelectromechanical component) along with structural interconnections that allow for Joule heating during manufacturing. In the illustrated contact heating embodiment, the DDS resonator is fixed between anchors by a multifunctional tether. That is, the tether not only mechanically fixes the DDS resonator to the anchors (and thereby to the device substrate), but also the Joule heating current (I JH It functions as a conductor for ) and, in some implementation configurations, as an insulator between the DDS resonator and the anchor.

[0063] The anchor itself may be mounted with or layered with a conductive material, and therefore a Joule heating current can be conducted from the wafer probe or singulated die probe. More specifically, a voltage source (or current source) established between two probes (i.e., potentials in either case indicated by v+ and v-) before encapsulation of the apparatus generates a Joule heating current flowing from left to right in the illustrated example, disengaging through the leftmost anchor and tether, through the DDS resonator, and then through the rightmost tether and anchor, thereby Joule heating the tether and DDS resonator. Also, although a DC current is shown in Figure 15A (and other subsequent figures), an AC current may be conducted through the DDS resonator.

[0064] Figure 15B shows an embodiment of a Joule-heated MEMS after encapsulation, in which conductive vias extend through the sealed encapsulation of the lid structure to make electrical contact with a conductive anchoring structure (i.e., the anchors are formed from or layered with a conductive material, as in Figure 15A). In this configuration, the Joule heating current may be driven through the DDS resonator during post-encapsulation finishing operations, or possibly even after manufacturing, including Joule heating in the field before or after the MEMS device is deployed in the host system. Figure 15C shows an alternative embodiment in which conductive vias extend through the device substrate (e.g., bulk semiconductor) to enable the flow of Joule heating current through the DDS resonator. Note that in both embodiments of Figures 15B and 15C, the sealed encapsulation, together with a surrounding sealing ring or similar structure, encloses a vacuum cavity or a cavity filled with an inert insulating material, thereby limiting thermal radiation from the DDS resonator to the substrate and lid.

[0065] Figures 16A to 16C illustrate embodiments of multifunctional tether structures, showing examples of bulk tethers (Figure 16A), composite tethers (Figure 16B), and extension path tethers (Figure 16C). Generally, the thermal and electrical resistance of a given tether structure is inversely proportional to its cross-sectional area, and the mechanical stiffness provided by the tether (i.e., for fixing a movable micro-machined component in relation to an anchor) increases with the cross-sectional area. In the bulk tether embodiment of Figure 16A, the width of the tether (W - a substitute for the cross-sectional area in embodiments having a depth dimension fixed according to the depth of the micro-machined component) is selected according to the thermal conductivity and electrical conductivity of the tether material and the extending distance (D) to provide not only desirable electrical and thermal resistance but also desirable mechanical stiffness. For example, the electrical and thermal resistance values ​​of a tether may be industrially designed to achieve a desired temperature range within the tether itself, thereby providing a thermal barrier (insulation) between a heated or overheated movable micro-machined component and an anchor and substrate at ambient temperature (or near ambient temperature).

[0066] In the embodiment shown in Figure 16B, the “composite” tether is implemented by an assembly of N component tethers (N>1), each sized to provide a desirable cross-sectional area in terms of extending distance, and to provide a predetermined degree of thermal insulation and mechanical stiffness. Depending on the intended movement of the movable micromachined member (e.g., different possible vibration modes within the resonant member), the decomposition of the bulk tether into multiple component tethers shown in Figure 16B can provide improved freedom of motion without excessively impairing mechanical support. The decomposition of the bulk tether into multiple component tethers collectively occupying the same footprint as the bulk tether reduces the cross-sectional area of ​​the composite tether (compared to a comparable bulk tether), thereby increasing the electrical and thermal resistance values ​​so that a relatively higher tether temperature—which may result in the realization of a relatively higher temperature within the target micromachined member—can be achieved with the same Joule heating current and manufacturing material.

[0067] In the embodiment shown in Figure 16C, the tether structure is routed laterally and folded in itself in a direction perpendicular to the extending distance, thereby extending electrical and thermal paths between the anchor and the movable micromachined member, which can result in significantly greater temperature and potentially greater thermal insulation. In the particular implementation shown, the tether includes a symmetrical lateral extension or fold (i.e., extending by a lateral distance L in both directions relative to the extension axis). With this configuration, and by selecting a collective lateral extension distance (2*L, where "*" indicates multiplication) that substantially matches the width of the movable micromachined member (or at least the width of the anchor), the tether presents an effective thermal barrier between the movable micromachined member and the anchor. In alternative embodiments, the lateral extension dimension of the folded tether may be only a portion of the width of the movable member (for example, 1 / 4 or 1 / 3 of the width of the movable member, but smaller or larger portions may be implemented), in which case it should be noted that multiple composite folded tethers can be deployed. Also, as described above, the width of the tether (W, which may be uniform throughout the base and lateral extension of the tether, or relatively narrower in one or the other) can be industrially designed to produce desirable thermal and electrical resistance values ​​and thereby generate relatively high temperatures within the tether, thereby increasing the effectiveness of the tether as an insulator (for example, the ratio of L to W may be set to 2, 3, 4, 5, or greater than these, or any decimal value between these integer ratios). Furthermore, the U-shape of each lateral (folded) extension provides a predetermined degree of mechanical compliance (another function performed by the tether), thereby compressing and expanding with the movement of the micro-machined component.Accordingly, the tether shown in Figure 16C functions to mechanically secure the movable micromachined member to the anchor, provide an electrical path for Joule heating, insulate the movable micromachined member from the anchor, and provide spring-like mechanical compliance between the micromachined member and the anchor. In alternative embodiments, the lateral extension dimension L (which may be less than, approximately equal to, or greater than, the extension distance D) may be greater than or less than that shown (for example, it may extend beyond the contour of the movable micromachined member), and the shape of the lateral extension may be different (for example, instead of a bend / fold to form a U shape, it may be radially curved in a semicircle or semiellipse). Alternatively, instead of symmetrical lateral extensions, the tether may have a single lateral extension (i.e., in only one direction in relation to the extension axis). Similarly, instead of a single tether having symmetrical lateral extensions and folds, the MEMS device may include two single foldable tethers having lateral extensions oriented in opposite directions (i.e., as if the illustrated tether were split into two along its extension axis), or it may include multiple pairs of such foldable tethers, such that the fold of one tether is included within the fold of another.

[0068] Figure 16D shows an illustrative thermal profile achieved by conducting a DC or AC Joule heating current through a movable micromachined component via an anchor and a folding tether. Due to the relatively high electrical resistivity of the tether in relation to the anchor and, in at least some cases, to the movable micromachined component, the Joule heating occurs primarily within the tether itself, resulting in conductive heating and possibly radiative heating (in which case Joule heating may also occur) of the movable micromachined component. Furthermore, the tether insulates the movable micromachined component from the anchor at or near ambient temperature (T0) during Joule heating, and as a result, in a vacuum environment, the nominal tether temperature at least at the physical midpoint of the tether (i.e., between the anchor and the micromachined component) is T0+T JH The temperature rises to 2 / 2, and the movable micro-machined component is at temperature T0+T JH The entire assembly will be heated relatively uniformly until the end. In alternative embodiments, other temperature profiles (including those with nonlinear gradients) may be generated. The movable micromachined component may be slightly cooler than the hottest part of the tether due to radiative losses or gas conduction, but will typically be near the highest temperature of the tether. Temperature profiles can be taken into consideration during the design and trimming processes.

[0069] Figure 17 shows another Joule heating MEMS embodiment, in which individual pairs of "flexible" tethers are provided to conduct Joule heating current to a movable micromachined member, with each such tether pair consequently forming a dedicated heating port. In this configuration, the mechanical tethers function to connect the micromachined member to anchors (two are shown, but a single anchor configuration is also possible) and to provide desired mechanical rigidity, although the flexible tethers can be designed to be relatively "soft," or in some cases as soft as possible, to minimize damping of vibration or inertial motion of the micromachined member. Furthermore, providing multiple pairs of flexible tethers also allows for non-uniform heating or overheating of individual areas of the micromachined member, which can be a useful effect in several applications. In alternative embodiments, more or fewer heating ports (flexible tether pairs) may be provided, including heating ports that drive current across corners, individual layers, or other further isolated areas of a micromachined component.

[0070] Figures 18A and 18B illustrate a heating configuration driven by an illustrative capacitance coupling, in which the electrodes, which function as drive and / or sense electrodes (e.g., in a MEMS resonator or accelerometer), also serve as a radio frequency (RF) energy input driving an AC Joule heating current within a movable micromachined member. In the embodiment of Figure 18A, for example, an RF energy source is supplied to both electrodes, and complementary phases of the RF signal (or, for example, a set of stable neutral voltages at the midpoint between the upper and lower peaks of the RF signal) are coupled to one or more multifunctional tethers, thereby realizing the flow of AC current between the multifunctional tether and the movable micromachined member. That is, energy is transferred from the RF energy source to the micromachined member via a capacitive coupling between the electrodes and the micromachined member, in which charge carriers (i.e., AC current) are alternately emitted and drawn between the electrodes and the micromachined member via the multifunctional tether.

[0071] In the embodiment shown in Figure 18B, the complementary phases of the RF energy source (or RF signal and neutral voltage) are coupled to two electrodes in an alternating manner, so that the electrodes are differentially driven to generate an AC current flow between them (i.e., charge carriers are forced across the movable micromachined member toward one electrode and then toward the other in an alternating manner). In such an embodiment, one (or more) mechanical tethers may be nonconductive (if they are conductive and coupled to a fixed-potential substrate via conductive anchors, the AC current will flow as in Figure 18A), and are industrially designed as described above to provide insulation in relation to one or more anchor structures having ambient or near ambient temperatures surrounding the die or wafer.

[0072] Figure 19A shows yet another Joule heating embodiment, in which energy is supplied to the individual layers of the multilayer device by conductivity (e.g., via the conductive tether described above) or by capacitance (e.g., via the capacitive electrodes described with reference to Figures 18A and 18B). In the particular example shown, the upper electrode layer and the lower DDS layer sandwich an internal dielectric layer (e.g., piezoelectric material) such that the outer layers can be considered to form individual resistance values ​​through which the DC or AC Joule heating current passes.

[0073] Figure 19B shows an alternative heating configuration in which Joule heating is primarily supplied within the patterned electrode layers of the dual silicon resonator (i.e., a degenerate doped poly layer and a degenerate doped single-crystal silicon layer having a piezoelectric layer sandwiched between silicon layers). The tether may still be structured to provide insulation between the resonator and the mooring field area, or otherwise have sufficient conductivity so that the main Joule heating voltage drop (and power dissipation) occurs within the patterned electrode layers. In the particular example shown, the patterned electrodes (e.g., implemented in one or both of the degenerate doped silicon layers—single-crystal silicon and / or polysilicon—with the latter configuration shown) include relatively narrow conductive passages extending between relatively large bulk interconnect nodes. Due to their relatively small cross-sectional area (and correspondingly relatively large resistance), the narrow passages are ohmic (I) within the conductive path traversed by the Joule heating current and therefore the main Joule heating source. 2 R) Constitutes the main source of power dissipation. Similar to the tether-based heating configuration in Figure 16D, the resonator maintains the target temperature (e.g., T0+T) through limited thermal radiation from the resonator to the substrate and lid structure. JH) can be heated relatively uniformly. More generally, patterned electrode Joule heating, either alone or in combination with other Joule heating or radiant heating sources, can produce a temperature profile different from the example in Figure 16D, which may involve the generation of localized or non-uniform temperature distributions.

[0074] Figure 20 shows another embodiment in which the RF energy source is coupled across the outer (at least reasonably conductive) layers of the movable micromachined member shown in Figure 19A. This configuration generates AC currents within the electrodes and DDS layers of the micromachined member to enable heating or overheating of those layers.

[0075] Figure 21 shows an encapsulated or chip-scale MEMS package having a MEMS die (for example, having a movable micro-machined component formed on its upper surface) and a control die. As shown, the control die includes not only several low-power control signal interconnects that carry relatively low-power runtime control and output signals between the two dies, but also relatively high-power thermal energy interconnects that enable the supply of Joule heating energy in forming DC or AC power signals. Although a single pair of thermal energy interconnects is shown, embodiments with multiple heating ports can provide even more interconnects. Also, although the thermal energy interconnects are shown extending between the control die and the MEMS die, instead of this, or in addition to this, the thermal energy interconnects may be exposed on the surface of the package to allow power supply from an external heating controller. Furthermore, the thermal energy interconnects between the MEMS die and the control die may be omitted due to an energy input interface on the MEMS die that is accessed pre- or post-encapsulation as described above (resulting in MEMS die heating being performed before packaging with the control die). Electrical vias and contacts sized for overheating may be larger in lateral dimensions than those designed for normal operation. For example, electric vias for normal operation may have a diameter of 5 to 15 microns to minimize parasitic capacitance. In contrast, vias sized for overheating may have a diameter in the range of 20 to 100 microns, for example, and without limitation, to minimize resistive heating within the via. The vias may be in contact with low-melting-temperature materials (such as aluminum or titanium), and therefore the increase in via temperature will be limited. Furthermore, the conductive material within the via may not be a low-doped semiconductor, but rather have a lower electrical resistivity than otherwise required for normal operation, such as a DDS.

[0076] Referring further to Figure 21, a programmable heating control circuit may be provided within the control die to enable in-situ post-manufacturing heating or overheating of one or more micromachined components within the MEMS die. In such an embodiment, the control die may also include a programming interface (i.e., a signaling interface) accessible via external contacts of the MEMS package. Accordingly, an external controller (e.g., a dedicated controller located in-situ with the MEMS package in a host system, or a standalone manufacturing or post-manufacturing controller) may be coupled to the programming interface to constitute the programmable heating control circuit and thereby issue the programming instructions and operands necessary to initiate and control the heating / overheating of one or more micromachined components within the MEMS die.

[0077] Figure 22 shows one embodiment of a programmable heating controller that may be used to implement the programmable heating control circuit of Figure 21. As shown, the heating controller includes several (N) programmable register banks that supply individual sets of programmed parameters to a power driver circuit. As a result, the power driver circuit drives power signals (i.e., those that function as voltage or current sources) to individual heating ports according to the parameters programmed in the corresponding register bank. In the particular example shown, each programmable register bank includes not only a set of register fields (any or all of which may be implemented by individual registers) for storing individual parameters that control the amplitude, duration, and frequency of the voltage or current pulses output by the power driver through the corresponding heating port, but also a port enable field that allows for the selective enabling or disabling of the heating ports.

[0078] Figure 23 shows a configuration in which multiple heating power drivers within an external heating controller are coupled to individual singulated or on-wafer MEMS devices, thereby enabling the simultaneous execution of the various heating and overheating operations described above in relation to the subject MEMS device. The external heating controller may be implemented, for example, within a manufacturing or test equipment (e.g., within automated test equipment (ATE)) capable of performing a number of other functions related to or independent of heating / overheating the MEMS device.

[0079] Figure 24A shows exemplary heating power profiles that can be generated in an external or in-situ heating controller as shown in Figures 22 and 23, along with exemplary temperatures generated within a movable micromachined component (i.e., within a MEMS device or package). In the particular embodiments shown, pulses of varying widths (durations) and amplitudes (powers) are generated such that the net energy supply is approximately proportional to the area under the pulse. More specifically, the pulse duration may be changed from at least 0.1 msec to 100 msec (in alternative embodiments, even shorter and / or longer pulse durations may be implemented), and the power level can range from at least 20 mW to 500 mW (even higher and / or lower limits may be supported). During heating / superheating operations, the temperatures generated within the movable micromachined element may significantly exceed the nominal MEMS runtime operating temperature, which ranges from 300 to 1300°C in the illustrative thermal profile shown, although even higher and / or lower temperatures (e.g., lower limit temperatures of 500, 600, 700, or 800°C) may be achieved.

[0080] Furthermore, although not shown in detail in Figure 24A, the pulse frequency may be changed according to heating control parameters (for example, as explained with reference to Figure 22). Also, as shown in Figure 24B, the power pulse waveform may be shaped to achieve a controlled cooling profile by, for example, selecting between various power-down ramp rates. Thus, if a relatively slow cooling rate is desired, a relatively long (relatively flat slope) power-down ramp may be selected, and conversely, if a relatively fast cooling rate is desired, a relatively short (relatively sharp slope) power-down ramp can be selected. The selected power-down ramp rate may be applied to all power pulses (in this case, different ramp rates may be applied to individual pulses), or it may be applied only to the final pulse or the final few pulses in the heating (power pulse) sequence. Furthermore, although a linear power-down ramp is shown, one or all of the ramps may also have a nonlinear profile (e.g., an exponential or hyperbolic profile). Furthermore, although a controlled power-down profile is shown, the rising edge of the power pulse may be shaped accordingly to achieve a controlled heating rate. In all cases, and without limitation, power profiles other than (or in addition to) the illustrated pulsed profile may be used to achieve apparatus heating operation including a stable or non-return-to-zero power profile.

[0081] Furthermore, the electrical circuit used to heat the structure can also detect the temperature of the structure. The electrical properties of the structure are generally a function of temperature; for example, resistance may increase with temperature. This may be used to measure the temperature before or after trimming. It may also be used to measure the temperature of the structure during or, in some cases, during the heating pulse. As a result, the pulse duration or height or other power profile characteristics may be changed beforehand or while it is progressing to obtain optimal results. For example, if the tether has a specific resistance when it is at a low temperature and a different resistance when it has a desired high temperature, the current pulse may be applied until the desired high temperature is reached. The resistance of the structure can be measured simultaneously with heating by various means, for example, by measuring a voltage across the structure to determine its resistance while applying a current to heat the structure, or alternatively, by measuring the resistance with an AC test signal while applying a DC heating drive.

[0082] Figure 25 illustrates an illustrative process for a packaged MEMS device, in which an oven reflow operation is performed to merge two separate terminals that form a heating port into a single operating terminal. That is, prior to the oven reflow, the packaged MEMS device includes three electrically insulated terminals, two of which form ports for heating or overheating the internal micro-machined structure as described above, and the other forming a first operating terminal. As the individual solder layers (or other layers of thermally soluble conductive material) of the two heating port terminals become fluid and flow together during the oven reflow, the two heating port terminals are effectively merged to form a second of the two operating terminals (i.e., the MEMS device is converted from a three-terminal device to a two-terminal device). This same method may be performed in relation to the first operating terminal (i.e., a reflow to merge a separate terminal that can configure a second heating port into the first operating terminal), or in relation to other terminals not shown.

[0083] Figure 26 shows an illustrative heating port configuration in a packaged MEMS device having two front terminals ("Terminal 1" and "Terminal 2"). In the particular embodiment shown, the back of the chip-scale package (CSP) is electrically coupled via a tethering structure to an electrode layer in a movable micromachined member (e.g., the resonant member shown in 119 of Figure 1), thereby forming a third terminal, referred herein as the "back terminal" ("Terminal 3"). One of the front terminals is electrically coupled via another tethering structure to the same electrode layer as the back terminal, such that the tethered front and back terminals form a heating port through which an AC or DC Joule heating current is conducted. Figure 27A shows an illustrative circuit model of this Joule heating operation, (each, R tether The current I flows through a pair of tethers (modeled as such) and further through one or more layers of the movable micro-machined component. JHThis is shown. Also, the current from terminal 1 to the lower (DDS) layer of the micro-machined component passes through one or more tether structures, and these tether structures may be the same tether structure that conducts the Joule heating current. For all terminal connections, an equal tether resistance value (R tether Although the values ​​shown are for tether resistance, it should be noted that tether resistance can vary from layer to layer, even when a shared tether is used. For example, the cross-sectional area (width and / or height) and / or conductivity of the tether may be non-uniform in relation to its connection to different layers of the micro-machined component.

[0084] Referring still to Figure 26, the capacitor between terminal 1 and terminals 2 / 3 represents, in this particular example, a piezoelectric or other dielectric thin film within the movable micromachined component. In the illustrated configuration, a DC current source is coupled across terminals 2 and 3 to generate a Joule heating current (e.g., during manufacturing or post-manufacturing processing), but a DC voltage source or an AC voltage or current source may be used instead. Furthermore, after dicing the wafer (i.e., the wafer containing the multiple such MEMS structures shown in Figure 26) into individual dies, the back of each die may still be electrically coupled to one of the front terminals (i.e., through the tether and the resistance of the movable micromachined component). In many applications, this residual electrical coupling (i.e., between the back and front terminals) has no effect (or only a negligible effect) on the operation of the device and may therefore be left as is. In applications where electrical insulation between the rear and front terminals of the device is required or beneficial during device operation, meltable or otherwise detachable connections to the rear terminals may be used to allow for the post-manufacturing disposal of the rear terminals.

[0085] The two front terminals shown in Figure 26 are used for normal device operation. In this example, the capacitor represents a piezoelectric layer, similar to the case of the dual silicon piezoelectric MEMS resonator shown in Figure 1A. During normal device operation, only one connection is required for each electrode layer (i.e., micromachined component) in the MEMS structure, and as a result, the back of the MEMS die (terminal 3) may not be used. In the illustrated illustrative model, the back terminal is permitted to be electrically floating, and as a result, no Joule heating current flows (or only a negligible Joule heating current flows) within the movable micromachined component. This operation is shown in Figure 27B. In alternative embodiments, the back terminal may be omitted as described above. Also, as with all embodiments herein, the micromachined component may be mounted / manufactured to have more or fewer layers than the three shown in Figure 26.

[0086] Figures 28A and 28B illustrate illustrative electrical interconnections between an encapsulation-level TSV (e.g., a through-silicon via extending through the encapsulation lid structure or substrate) and a piezoelectric resonator electrode that enables both package-level terminal interconnections of the MEMS resonator (i.e., in the subsequent packaging step) and post-encapsulation Joule heating. In the embodiment of Figure 28A, three terminals are exposed in the TSV through the lid and / or substrate layer of the encapsulated dual silicon resonator, two terminals are coupled to the lateral end opposite the upper electrode (shown as an ISDP layer, but any alternative material layer configuration may be used), and one terminal is coupled to the lower electrode (in this example, a degenerate-doped single-crystal silicon layer). In this configuration, DC or AC may pass, for example, through the tethering structure and upper electrode layer of the resonator, and either or both of the tethering structure and upper electrode layer of the resonator may be designed to overheat the resonator material laminate (i.e., to Joule heat the resonator material laminate as described above), thereby performing any number of post-encapsulation annealing operations and / or thermal frequency trim operations. The embodiment in Figure 28B is similar to that in Figure 28A, except that the Joule heating terminal pair is tethered to the opposite lateral end of the lower electrode layer (e.g., a degenerate-doped single-crystal silicon layer) to operate the lower tethering layer and / or lower electrode layer as a superheating source, instead of the upper layer tether / electrode element. In further embodiments, two Joule heating terminal pairs may be provided, each coupled to the opposite end of an individual degenerate-doped silicon layer. Furthermore, as will be described in more detail below, the Joule heating terminal pair in either embodiment of Figure 28A / Figure 28B may be merged with the third encapsulation terminal to form a resonator detection / drive terminal as described with reference to Figure 1A. Alternatively, the Joule heating terminal pair may be driven by an equipotential resonator drive signal to emulate the electrical coupling of the terminal pair.That is, instead of wiring a single terminal to establish equipotential at the lateral edges of the relevant material layer (and tethering layer), the terminal may be driven to equipotential by the drive / sensor circuit of the mounted logic die.

[0087] Figures 29A and 29B illustrate a terminal reduction scheme in which three or more encapsulation-level terminals (as described, for example, with reference to Figures 28A and 28B) are merged before encapsulation within the package housing to expose only two electrically independent package-level terminals. In the conceptual diagram of Figure 29A, the Joule heating terminals (Joule heating ports) are coupled to the ISDP layer of the dual silicon resonator (allowing the introduction of Joule heating current through a wafer probe or singulated die probe), but they may instead be coupled to the core single-crystal resonator layer, or complemented by additional heating ports coupled to the core resonator layer (i.e., in a four-terminal encapsulation structure).

[0088] Figure 29B shows an illustrative sequence of packaging operations to achieve the in-package terminal merge (reduction) shown in Figure 29A, with cross-sectional and plan views of the encapsulated or packaged structure at each point in the sequence. Beginning with an illustrative three-terminal encapsulated structure, two Joule-heated terminals are merged by metal deposition to form an integrated upper electrode terminal (or lower electrode terminal). Subsequently, a further packaging layer (e.g., polyimide or other non-conductive molding or material layer) is placed on the merged electrode terminals, with through vias and solder ball sockets formed as shown, to obtain a four-terminal package in which two of the package-level terminals are electrically common (for each terminal-merge metal deposition) to form an upper electrode interconnect node, and a third of the four terminals is coupled to the lower electrode (or vice versa). The fourth package-level terminal is primarily provided for mechanical stability and may be left unconnected ("unconnected" or "NC"), or it may be redundantly coupled to the lower or upper resonator electrode. In further embodiments, particularly when a rectangular packaging structure is desired, only two package-level contacts—one for each of the two resonator electrodes—can be exposed.

[0089] In systems based on resonators for timing, sensing, or other applications, it may be desirable to calibrate the resonant frequency at or near room temperature to compensate for variability in the resonator manufacturing process. For example, the room-temperature resonant frequency of an uncalibrated resonator may differ from its desired frequency by + / - 10,000 ppm compared to the typical application requirement of + / - 20 ppm (parts per million) or less.

[0090] The offset between the desired resonant frequency and the actual resonant frequency can be eliminated through active compensation (i.e., continuous correction) or through passive compensation (i.e., one-degree correction or "trim"). Active compensation methods are undesirable because they require dedicated electronic circuitry, consume power, and the noise at the compensated frequency output may be greater than that at the uncompensated resonator frequency.

[0091] For several reasons, it is advantageous to perform frequency calibration after the resonator has been sealed and packaged. Firstly, this can be done in a non-cleanroom environment, resulting in reduced costs. Secondly, the packaging process may slightly shift the resonator frequency, which would degrade the accuracy of the frequency trimming process.

[0092] For example, passive compensation techniques have been developed to trim the room-temperature frequency of MEMS resonators through mass removal / addition via laser irradiation or surface chemical reactions. However, when applied to sealed packaged resonators, these techniques have several limitations (e.g., package damage, generation of particulate matter in the sealed cavity, introduction of chemically reactive materials in the sealed cavity, increased cavity pressure, increased process complexity / cost, etc.).

[0093] In some embodiments disclosed herein, various Joule heating structures / techniques and / or alternative heating techniques (such as overheating by laser or other electromagnetic radiation) described above are applied to achieve thermal frequency trimming operation. More generally, the application of a heating method involves modifying one or more resonant frequencies or other resonant device characteristics based on changes in material properties—changes separate from the removal, excision, dimensional changes, or surface modifications of the material described above. These changes may occur as side effects of heating to modify material properties, but they are not the primary mechanism for achieving frequency trimming. One or more heating cycles in a sequence may be used to manipulate the resonant frequency of the MEMS structure. These and other thermal trimming embodiments and features are disclosed in further detail below.

[0094] Figure 30 illustrates heating of a MEMS resonator via a source of electromagnetic radiation, such as a laser (e.g., a continuous-wave or pulsed laser with wavelengths in the ultraviolet-infrared range) or other electromagnetic radiation. The MEMS resonator can optionally be sealed and encapsulated before frequency modification to compensate for frequency shifts induced by encapsulation. The sealed enclosure can be fabricated from silicon, glass, alumina, or other materials that have minimal optical absorption at a particular wavelength compared to the DDS housing the MEMS structure. For example, an IR laser (e.g., 1.1 micron wavelength) can be used to significantly increase the absorption of the DDS layer within the MEMS resonator (e.g., implemented by the dual-silicon resonator or its modification as described above) compared to a low-doped silicon sealed enclosure (e.g., 1e17 atoms / cm³). 3) can be combined with the laser. The laser can heat the resonator while leaving the sealed encapsulation relatively undamaged. In the case of a laser beam, the spot size may be substantially round or may have alternative shapes through optical manipulation. The spot size is usually significantly smaller than that of the MEMS structure, but in some cases it may be beneficial to use a laser spot that is comparable in size to the structure. The laser spot may be applied to one or more distinct locations on the structure, or it may be scanned to heat a specific area, shape, or pattern.

[0095] In the case of heating via electromagnetic radiation, the DDS layer can perform two functions: frequency tuning through stiffness modification and optical absorption. Alternatively, the DDS layer can be used for a single function (optical absorption), and the frequency of the MEMS structure can be modified through laser removal, resulting in a change in shape that leads to a decrease in stiffness or mass depending on the spatial distribution of removal. The optical power may be spatially patterned across the MEMS structure, for example, to independently industrially design room temperature frequencies for two or more modes, or to independently control two or more frequency temperature coefficients.

[0096] In laser-based heating methods, the tether performs two functions (thermal shielding / insulation and mechanical compliance), and the importance of its third potential function—providing a relatively large electrical resistance—is relatively small. The heating power source is located at the point of laser incidence, rather than within the hotspot of the tether or patterned electrode, as in the case of Joule heating.

[0097] Figures 31A and 31B illustrate the manipulation of electroactive dopant concentrations through heating and cooling processes applied to MEMS resonator structures. The total dopant concentration in a semiconductor is the sum of electroactive and non-electroactive dopant concentrations. Within DDS materials, the electroactive dopant concentration at the completion of wafer scaling can be significantly lower than the total dopant concentration through numerous dopant deactivation mechanisms.

[0098] The manufacturing process for DDS can be industrially designed so that high concentrations of dopant become electrically inert at the completion of the wafer manufacturing process. The inert dopant concentration can be controlled through the selection of dopant species (e.g., arsenic, boron, phosphorus, or antimony), dopant dosage / unit area, dopant concentration distribution, or heat treatment parameters applied to the resonator (e.g., time, temperature, heating rate, cooling rate).

[0099] Figure 16A shows the electroactive dopant concentration after heating such a DDS sample (e.g., degenerate-doped single-crystal silicon or degenerate-doped polycrystalline silicon). The electroactive dopant concentration does not change significantly at low temperatures (e.g., below 200°C), but increases dramatically at relatively higher temperatures until a large proportion, or potentially substantially all, of the pre-inactive dopants become activated by heat. The maximum heating temperature can be anywhere between 600°C and 1300°C.

[0100] Figure 31B shows two potential scenarios for electroactive dopant concentration as the DDS cools. At sufficiently slow cooling rates (e.g., 1°C / min), the electroactive dopant concentration will decrease as the dopants are inactivated, for example, in the case of phosphorus doping, through the formation of inactive clusters. After slow cooling to room temperature, a large proportion of the dopant atoms may become inactive. In contrast, if the DDS is cooled to 10°C / min, 4When rapid cooling ("quenching") occurs at a rate of °C / second (and even smaller or larger cooling rates may be effective), a relatively small number of dopant atoms will be inactivated. To reduce the electroactive dopant concentration, subsequent heating to a relatively lower temperature or a relatively slow cooling rate may be used, thereby increasing or decreasing the dopant concentration. Therefore, to manipulate the electroactive dopant concentration in a DDS, a cycle of heating followed by rapid cooling ("heating cycle," "superheating cycle," or "heating / quenching cycle") can be used.

[0101] Figure 32A shows the relationship between the resonant frequency and the electroactive dopant concentration of the DDS. The electroactive concentration of carriers in the DDS is related to its stiffness at room temperature (e.g., c in silicon). 11 , c 12 and c 14 Both the coefficient and its first, second, and even higher-order stiffness temperature coefficients can be changed. Therefore, changes to the electroactive dopant concentration of the DDS can be used for frequency trimming.

[0102] Figure 32B shows the variation in the room-temperature resonant frequency with respect to heating time and heating temperature. The rate of change of the frequency changes exponentially with heating time and usually saturates at the stable state frequency after a sufficiently long heating time. Increasing the heating temperature is usually associated with a decrease in the resonant frequency. However, as mentioned above, it is possible to potentially reduce the active dopant concentration (increase the resonant frequency) by heating the MEMS device to a specific temperature and then subsequently heating the device to a lower temperature; this is a technique referred to herein as "back-tuning".

[0103] Temperature-activated material changes in MEMS structures are not specific to any particular transduction technique. For example, this can be readily applied to devices that are transduced electrostatically, piezoelectrically, piezoresistively, or magnetically. Similarly, this is not specific to Joule heating or laser-based heating. Any other heating method that can controlly heat the MEMS structure to a sufficiently high temperature may be applied. In the case of laser beam heating, in some cases, if the electrodes are located on the resonator, it may be advantageous to position the laser beam in an area not covered by the electrodes. For example, in a piezoelectric resonator, electrodes can be used on the resonator. The resonator may be industrially designed so that certain areas of interest, such as areas experiencing large strains or large motions in vibration modes, are located away from the electrodes to avoid damage to the electrode surface associated with laser illumination.

[0104] Figure 33 shows an illustrative sequence of heating (power) pulses continuously applied to a MEMS resonator to iteratively change its resonant frequency. In this particular example, after three similar heating pulses have been applied to the structure, the frequency has saturated and is no longer decreasing. The heating power and duration of the fourth pulse are increased, resulting in a further decrease in the resonant frequency.

[0105] The temperature of a MEMS structure in a thermal process can be controlled by changing the applied power and / or the duration of the applied power level. For example, applying a thermal pulse with a duration of 1 nanosecond (nsec) to a MEMS structure with a characteristic thermal time constant of 1 millisecond (msec) results in a significantly lower maximum temperature than a 100-millisecond pulse, because in the former case, the structure does not reach thermal equilibrium. The thermal time constant of a MEMS structure can be engineered through the shape or material of the structure.

[0106] Figure 34 is a flowchart illustrating an illustrative frequency trimming procedure or algorithm. This routine begins by measuring the resonant frequency of the resonator at one or more temperatures. The temperature can be adjusted by using an external source or by passing an electric current through the apparatus (i.e., either the radiant heating or Joule heating techniques disclosed herein, and more generally, any applicable technique for heating the MEMS structure). If the resonator is not operating in the desired manner, the heating power, exposure duration, and spatial distribution of the thermal process are calculated to modify the resonator characteristics. The thermal process is applied to the MEMS structure, for example, through Joule heating or laser radiation. After waiting for a period of time until the MEMS structure reaches a desired temperature, such as the temperature of the surrounding room, the resonant frequency is measured again to determine whether the desired operation has been achieved. The resonant frequency may be measured when the resonator is at a high temperature, but this will result in an offset between the measured frequency and the room temperature frequency. Therefore, it is preferable to measure the resonant frequency at a temperature that represents the target application.

[0107] In practice, frequency trimming consists of multiple repeated cycles (iterations) comprising measuring the resonant frequencies of one or more eigenmodes at one or more temperatures, followed by the application of a thermal process to the MEMS structure to impart a change in the room temperature frequency or TCF of one or more modes. By changing the thermal process characteristics (e.g., maximum temperature or duration) or the spatial distribution of the thermal process (e.g., laser position, AC frequency, or active electrical terminals), multiple parameters (e.g., frequencies of two different resonant modes, or room temperature frequency and primary TCF) can be changed independently. In the thermal measurement cycle in which each iteration consists, it is beneficial, though not essential, to allow a sufficiently long waiting period after the heating cycle for the MEMS structure has cooled to ambient temperature or a known temperature before measuring the frequency. The temperature of the MEMS structure can be estimated by passing a relatively small current through the structure to measure its electrical resistance, which changes with temperature. Alternatively, various optical or other non-contact temperature measurement techniques (e.g., a vibrometer that identifies the resonant frequency in conjunction with the application of a power pulse) may be used to determine the overheating temperature, and / or an in-situ temperature sensing structure may be used to determine the overheating temperature. However, if detected, the overheating temperature may be fed back to a heating control circuit to enable closed-loop heating of the MEMS structure to the target frequency and to control the heating and / or quenching grade / profile.

[0108] After each thermal measurement cycle, parameters for the next cycle can be calculated. This process may be assisted by a model-based approach, in which case the expected frequency change for the thermal process is calculated and compared with the measured frequency change. If the magnitude of the frequency change in a particular iteration is smaller than expected, the thermal power of the next iteration can be increased to compensate. Similarly, the thermal power of the next iteration can be modified by using a larger-than-expected frequency change. This feedback process can reduce the number of iterations and, therefore, the cost of frequency trimming.

[0109] Figure 35 illustrates an exemplary frequency trimming procedure. At the start of each iteration, the resonant frequency is measured, and the thermal process to be applied is calculated. Initially, the frequency is above the target frequency. Initially, the thermal power is small to avoid excessive frequency adjustment and to potentially calibrate the mathematical model for the characteristics of this particular resonator. Over a total of seven iterations, the thermal power is gradually increased and the frequency is gradually decreased until the target frequency is achieved. The frequency trimming process may be terminated when the resonant frequency falls within an acceptable range, or alternatively, it may be stopped if the number of iterations exceeds a prescribed limit, or if the frequency moves too far from the target frequency with a high probability of success.

[0110] Figure 36 shows an illustrative frequency trimming procedure, including a frequency back-tuning technique. As mentioned above, thermal frequency tuning of a DDS can be inverted under certain circumstances. The ability to invert the tuning process allows for the use of relatively aggressive frequency trimming algorithms. In this example, the thermal power is rapidly increased. After the third cycle, the resonant frequency is below the target frequency. The remaining two iterations reduce the thermal power to increase the frequency until the target frequency is realized.

[0111] To save time and reduce manufacturing costs, multiple structures can be trimmed simultaneously. For example, an electrical probe station can be constructed to simultaneously measure and trim two, four, eight, or various other numbers of devices. Alternatively, or in combination, multiple structures may be electrically contacted simultaneously and trimmed continuously.

[0112] The frequency tuning process may be used to trim multiple system parameters simultaneously and is not limited to the resonant frequency of a single resonant mode at room temperature. For example, the room temperature of multiple resonant modes, multiple temperature coefficients of a single mode, or any combination of these can be adjusted. This is possible by controlling the spatial temperature distribution across the MEMS structure in the thermal modification process. For example, consider two positions P1 and P2 on a resonator and two vibration modes M1 and M2. The change in the frequency of each eigenmode due to a change in stiffness at a particular position is proportional to the mechanical stress at that position. For example, the mechanical stress at P1 may be small for M1 and large for M2. In the case of P2, the opposite may be true in relation to M1 and M2. Therefore, changing the stiffness at P1 will favorably change the frequency of M1, and changing the stiffness at P2 will favorably change the frequency of M2. This concept of distinct positions can be generalized to a continuous temperature and stress distribution across the MEMS structure.

[0113] Exemplary methods for controlling and altering the temperature distribution across a MEMS structure include changing the position of an incident laser beam, changing the selection of active and reactive electrical terminals used for heating, or changing the frequency of an AC input to alter the distribution of current flowing through the device, thereby resulting in an increase in temperature in relation to the current passing through dispersed parasitic capacitances.

[0114] Figures 37A–37D illustrate illustrative operations of multiple resonant frequencies within a MEMS structure based on heating by a subset of all available heating terminals. Figure 37A shows a simplified disk ring gyroscope along with the two vibration modes of interest, Mode 1 and Mode 2. Figure 37 shows an illustrative array of electrodes surrounding a MEMS structure, which can be used in capacitance-coupled Joule heating in addition to their use in potential normal device operation. Figure 37C shows RF inputs applied to a subset of electrodes so that the MEMS structure is heated non-uniformly to preferentially tune the frequency of Mode 1, and Figure 37D shows RF inputs applied to different subsets of electrodes to preferentially adjust the frequency of Mode 2 to obtain a desired frequency relationship between the two modes. Temperature-initiated frequency trims can be used to manipulate the sum or product of two or more vibration modes. Illustrative applications, without limitation, include mode matching, industrial design of frequency differences between two modes, and control of frequency ratios between two modes.

[0115] Figure 38 illustrates the modulation of the frequency relationship between two modes of a similar MEMS structure based on the activation of a subset of heating terminals, except that Joule heating is achieved through terminals directly coupled to the structure, thereby allowing the possibility of DC heating currents.

[0116] The dopant concentration in the DDS layer or within the DDS layer can be varied across the MEMS structure. For example, regions with high electrical resistivity can be introduced into the structure to increase the local Joule heating power density. Another application is that variations in dopant concentration across the structure can allow for localized changes in overheating-induced mechanical stiffness, even when the temperature is relatively uniform across the structure. This can be used to industrially design one or more temperature coefficients (TCFs) of the structure's frequency. For example, a MEMS resonator can be formed from two or more mechanically and thermally coupled regions, but with substantially different TCFs. The room-temperature frequency and TCF of the composite structure will depend on the weighted contributions from each region. Thus, a change in the mechanical stiffness of one region in relation to the other region will result in a change in the TCF of the composite structure.

[0117] Furthermore, by using asymmetrical changes in the stiffness of the MEMS structure, it is possible to induce a change in the quality factor (Q) of the resonator. Asymmetrical changes in the mass or stiffness of the resonator result in increased energy loss at the point where the resonator is connected to the substrate or package. As a result, Q is reduced. If the resonator is designed to be asymmetric, and the laser modifies the resonator to eliminate the asymmetry, Q may increase. The Q level of the system can be calibrated, for example, by adjusting the spatial distribution of temperature during heat treatment, either through the laser position or through the active electrical terminals.

[0118] Various circuits and MEMS structures disclosed herein may be described using computer-aided design tools in terms of their operation, register transfers, logic components, transistors, layout shapes, and / or other characteristics, and may be represented (or expressed) as data and / or instructions executed in various computer-readable media. Formats of files and other objects in which such circuit representations may be implemented include, without limitation, formats supporting operational languages ​​such as C, Verilog, and VHDL; formats supporting register-level description languages ​​such as RTL; and formats supporting shape description languages ​​such as GDSII, GDSIII, GDSIV, CIF, MEBES, and any other suitable formats and languages. Computer-readable media in which such formatted data and / or instructions may be executed include, without limitation, various forms of computer storage media (such as optical, magnetic, or semiconductor storage media, regardless of whether they are independently distributed in that manner or stored "in location" within an operating system).

[0119] When received within a computer system via one or more computer-readable media, such representations of the circuits described above, based on such data and / or instructions, can be processed by processing entities within the computer system (e.g., one or more processors) in connection with the execution of one or more other computer programs, including netlist generation programs, location and root programs, and similar ones, to generate representations or images of the physical manifestations of such circuits. Such representations or images can then be used in device manufacturing, for example, by enabling the generation of one or more masks used to form various components of the circuits in the device manufacturing process.

[0120] In the above description and in the accompanying drawings, specific terminology and drawing symbols are used to provide a full understanding of the disclosed embodiments. In some examples, terminology and symbols may refer to specific details that are not necessary for carrying out the embodiments. For example, certain dimensions, quantities, temperatures, durations, signal levels, power levels, signaling or operating frequencies, component circuits or devices, and similar items may differ in alternative embodiments from those described above. In addition, links or other interconnections between integrated circuit devices or internal circuit elements or blocks may be shown as buses or as single signal lines. Each bus may instead be a single signal line, and each single signal line may instead be a bus. However, the illustrated and described signal and signaling links may be single-ended or differential. A signal drive circuit is described as one that “outputs” a signal to a signal receiver circuit when the signal drive circuit asserts (or, if explicitly indicated or shown in the context, deassers) a signal on a signal line coupled between the signal drive circuit and the signal receiver circuit. The term “coupled” is used herein to describe not only direct connections but also connections through one or more intervening circuits or structures. Device “programming” may include, for example and without limitation, reading control values ​​into registers or other storage circuits in an integrated circuit device in response to a host instruction (and thus control of the device’s operating mode and / or establishment of the device configuration) or through a one-time programming operation (e.g., blowing a fuse in the configuration circuit during device manufacturing), and / or connecting one or more selected pins or other contact structures of the device to a reference voltage line (also called a strapping) in order to establish a particular device configuration or operating mode of the device. The terms “exemplary” and “embodiment” are used to represent an example, not a preference or requirement.Furthermore, the terms "may" and "can" are used interchangeably to indicate optional (acceptable) subjects. The absence of either term should not be interpreted as meaning that a given feature or technique is essential.

[0121] Various modifications and alterations can be made to the embodiments presented herein without departing from the broad spirit and scope of this disclosure. For example, any feature or aspect of any embodiment can be applied in combination with any other embodiment, or in place of a comparable feature or aspect. Accordingly, this specification and the accompanying drawings should be considered illustrative, not restrictive.

Claims

1. It is a method, The present invention provides an integrated circuit device having a micro-electromechanical system (MEMS) vibrating structure, a first external pin or contact, a second external pin or contact, a heating element, and a circuit, wherein the MEMS vibrating structure is characterized by a resonant frequency, the first external pin or contact outputs an output signal corresponding to the resonant frequency, the integrated circuit device further comprises at least one structure having material properties that are altered under heating, the resonant frequency depends on the material properties, and the second external pin or contact is adapted to cause the heating element to heat the at least one structure. As part of a calibration operation for the integrated circuit device, the output signal is measured to identify the deviation between the output signal and a target value, and in response to the identification of the deviation, one or more electronic signals are applied to the second external pin or contact to heat the heating element to the at least one structure in a manner that reduces the deviation, so that during the execution time of the integrated circuit device, the at least one output signal is generated with a smaller deviation. Methods that include...

2. The method according to claim 1, wherein the integrated circuit device is a packaging device having one or more dies, each of the first external pins or contacts is on the outer surface of the packaging device, and the MEMS vibration structure is on the first die of the one or more dies.

3. The method according to claim 1, wherein the at least one structure comprises one or more layers of the vibrating structure, and the heating element is adapted to heat the one or more layers by Joule heating.

4. The method according to claim 1, wherein the target value includes the frequency of the output signal at a predetermined operating temperature, and the measurement further includes performing the measurement at the predetermined operating temperature.

5. The aforementioned integrated circuit device further comprises electronic storage, and the method is Further includes identifying the temperature-dependent behavior associated with the output signal, The aforementioned method, The frequency of the output signal is measured at several other temperatures different from the predetermined temperature, and the deviation between the frequency of the output signal and the predetermined resonant frequency at each of the several other temperatures is identified. The correction polynomial corresponding to each of the aforementioned deviations is calculated, The parameters defining the correction polynomial are programmed into the electronic storage so that the integrated circuit device stores the correction polynomial for application during the execution time of the integrated circuit device. The method according to claim 4, further comprising:

6. The method according to claim 5, wherein the integrated circuit device further comprises a temperature sensor and a signal conditioning circuit, the signal conditioning circuit receives a detection signal corresponding to the movement of the MEMS vibration structure during the execution time of the integrated circuit device, generates the output signal corresponding to the detection signal, and the signal conditioning circuit is configured to electronically correct the frequency of the output signal on an internal base of the integrated circuit device during the execution time of the integrated circuit device, within the operating temperature range of the integrated circuit device, according to the temperature detected by the temperature sensor and the correction polynomial.

7. The method according to claim 6, wherein the MEMS vibration structure is part of a first MEMS resonator, the temperature-dependent behavior is a first temperature-dependent behavior, the temperature sensor comprises the first MEMS resonator and a second MEMS resonator, the second MEMS resonator has a second temperature-dependent behavior, and the integrated circuit device comprises a circuit that can be operated to identify the temperature detected by the temperature sensor as a function of the difference between the second temperature-dependent behavior and the first temperature-dependent behavior.

8. The method according to claim 1, wherein the MEMS vibration structure is a resonant structure comprising at least a layer of crystalline silicon, a conductive layer, and a piezoelectric layer, and the method further comprises, during the calibration operation, causing the application of a drive signal to the conductive layer to vibrate the MEMS vibration structure in accordance with the piezoelectric layer.

9. The method according to claim 1, wherein the integrated circuit device is encapsulated, and the integrated circuit device further comprises a temperature sensor and a third external pin or contact, and the method further comprises receiving a temperature indication detected from within the encapsulated integrated circuit device via the third external pin or contact during the calibration operation, and the application of one or more electronic signals comprises selecting a signal corresponding to the detected temperature indication and applying the selected signal.

10. The method according to claim 1, wherein the one or more electronic signals include pulsed signals having a frequency of at least 1 kilohertz.

11. The method further includes a bidirectional frequency tuning process, wherein the application of the one or more electronic signals is Applying a first electronic signal to the second external pin or contact, the heating element heats the at least one structure in such a manner that it reduces the first of the positive or negative deviations. Applying a second electronic signal to the second external pin or contact, the heating element heats the at least one structure in such a manner that it reduces the second of the positive or negative deviations. The method according to claim 1, comprising selectively including one of the following.

12. The method according to claim 1, wherein receiving the integrated circuit device further comprises manufacturing the MEMS vibration structure using a semiconductor manufacturing process.

13. It is a method, The purpose is to receive an integrated circuit device, and the integrated circuit device is A first die having a micro-electromechanical system (MEMS) vibration structure, A second die having a circuit, A first external pin or contact, A second external pin or contact is provided, The aforementioned integrated circuit device further includes a heating element, The aforementioned MEMS vibration structure is characterized by its resonant frequency. The first external pin or contact outputs an output signal corresponding to the resonant frequency. The aforementioned integrated circuit device further comprises at least one structure having material properties that are altered under heating, The aforementioned resonance frequency depends on the material properties, The second external pin or contact is adapted to cause the heating element to heat the at least one structure, As part of a calibration operation for the integrated circuit device, the output signal is measured to identify the deviation between the output signal and a target value, and in response to the identification of the deviation, one or more electronic signals are applied to the second external pin or contact to heat the heating element to the at least one structure in a manner that reduces the deviation, so that during the execution time of the integrated circuit device, the at least one output signal is generated with a smaller deviation. Methods that include...

14. The method according to claim 13, wherein the integrated circuit device is an encapsulation device, each of the first external pins or contacts is located on the outer surface of the encapsulation device, and the measurement is performed by electrically coupling the first external pins or contacts to a receiving device, thereby the measurement is performed regardless of the presence of encapsulation.

15. The method according to claim 13, wherein the at least one structure comprises one or more layers of the vibrating structure, and the application includes applying at least a 1-kilohertz signal to the second external pin or contact to heat the heating element, thereby heating the one or more layers by Joule heating.

16. The target value includes the frequency of the output signal at a predetermined operating temperature, and the measurement further includes performing the measurement at the predetermined operating temperature. The aforementioned integrated circuit device further comprises electronic storage, The aforementioned method, The frequency of the output signal is measured at several other temperatures different from the predetermined temperature, and the deviation between the frequency of the output signal and the predetermined resonant frequency at each of the several other temperatures is identified. The correction polynomial corresponding to each of the aforementioned deviations is calculated, The parameters defining the correction polynomial are programmed into the electronic storage so that the integrated circuit device stores the correction polynomial for application during the execution time of the integrated circuit device. The method according to claim 13, further comprising:

17. The method according to claim 16, wherein the integrated circuit device is configured such that the correction polynomial is applied internally by the integrated circuit device, and the integrated circuit device is configured such that the first external pin or contact outputs a temperature-compensated output signal during execution time.

18. The method according to claim 13, wherein the MEMS vibration structure is a resonant structure comprising at least a layer of crystalline silicon, a conductive layer, and a piezoelectric layer, and the method further comprises, during the calibration operation, causing the application of a drive signal to the conductive layer to vibrate the MEMS vibration structure in accordance with the piezoelectric layer.

19. The method further includes a bidirectional frequency tuning process, wherein the application of the one or more electronic signals is Applying a first electronic signal to the second external pin or contact, the heating element heats the at least one structure in such a manner that it reduces the first of the positive or negative deviations. Applying a second electronic signal to the second external pin or contact, the heating element heats the at least one structure in such a manner that it reduces the second of the positive or negative deviations. The method according to claim 13, comprising selectively including one of the above.

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