Inertial MEMS device integrated with wake-up element, inertial MEMS system and method of manufacture
By introducing wake-up elements of movable structure, suspended structure and piezoelectric structure into the inertial MEMS device, and adjusting the consumption mode using signal thresholds, the problem of high energy consumption in the inertial MEMS device in a stationary state is solved, and efficient wake-up of the device is achieved and low-energy operation.
Patent Information
- Application Number
- CN202410791447.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-06-12
- Filing Date
- 2024-06-19
- Publication Date
- 2024-12-24
AI Technical Summary
The existing inertial MEMS devices remain active in a static state, resulting in energy consumption that cannot be ignored, limiting their use in low consumption and long-term applications, and the existing activation structure increases the device size and the energy consumption does not meet application requirements.
Using wake-up elements including movable structure, suspended structure and piezoelectric structure, by generating activation signals during vibration or impact, the control circuit determines low-consumption or high-consumption operating modes based on the signal threshold, and realizes efficient wake-up and sleep of inertial MEMS devices. state.
It effectively reduces the energy consumption of inertial MEMS equipment in a static state, reduces the equipment size, and dynamically adjusts the consumption mode according to environmental changes to adapt to different application needs.
Smart Images
Figure CN119178431A_ABST
Abstract
Description
[0001] Priority claim
[0002] This application claims the benefit of priority from Italian Patent Application No. 102023000013002, filed on June 23, 2023, the contents of which are hereby incorporated herein by reference in their entirety to the maximum extent permitted by law. Technical Field
[0003] The present invention relates to an inertial micro-electromechanical system (MEMS) device integrated with a wake-up element, an inertial MEMS system and a manufacturing method.
[0004] In particular, the inertial MEMS device under consideration comprises one or more inertial sensors, such as accelerometers and / or gyroscopes, formed in at least one silicon structural layer and defining at least one movable structure. The movable structure as a whole has a main extension in an extension plane and is movable in or out of the plane. Background Art
[0005] As is known to all, inertial micro-electromechanical systems (MEMS) devices are increasingly being used in consumer, automotive and industrial applications. MEMS devices typically integrate two or more inertial sensors in the same die and are packaged together with related control circuits. The control circuits are typically formed in a separate die and form an application-specific integrated circuit (ASIC), which is also referred to as the control circuit hereinafter.
[0006] In many applications, it is often desirable for an inertial MEMS device to be always active, to be able to sense movement and / or changes in the surrounding environment in real time.
[0007] To this end, the control circuit is usually always turned on. When the system is at rest, the control circuit keeps the inertial MEMS device in a low-consumption state (low operating frequency) so that it can sense environmental changes and generate an interrupt signal; when the interrupt signal is received, the control circuit activates the normal (high-frequency and high-consumption) operation of the system.
[0008] Thus, even in the stationary state of the system, the inertial MEMS device is kept active (or "awake"), which has a non-negligible consumption even at low frequencies. However, this is undesirable, since it prevents or at least limits the use of such systems in applications and conditions requiring low consumption and / or long duration, without the need for an external power source.
[0009] To overcome this problem, it has been proposed to provide an activation or "wake-up" structure that is arranged side by side with the inertial MEMS device, integrated in the same die or in a suitable adjacent die. In a static state, the inertial MEMS device is off and does not consume. When an environmental change occurs, the activation structure senses the environmental change and sends a signal to the control circuit, which activates the inertial MEMS device.
[0010] However, this arrangement increases the size of the entire device. In addition, sometimes, the total energy consumption is still too high compared to the energy consumption expected in some applications.
[0011] There is a need in the art to provide solutions that overcome the shortcomings of the prior art. Summary of the invention
[0012] Embodiments herein relate to inertial MEMS devices, inertial MEMS systems, and manufacturing methods.
[0013] In an embodiment, an inertial MEMS device includes: an inertial element that responds to movement, the inertial element including a movable structure, the movable structure being formed in a first structural layer of a semiconductor material; a suspended structure, the suspended structure extending above the movable structure and at a certain distance from the movable structure, the suspended structure being formed in a second structural layer of the semiconductor material; and a piezoelectric structure, the piezoelectric structure being arranged on the suspended structure, the suspended structure and the piezoelectric structure forming a wake-up element, and the wake-up element is configured to generate an activation signal in the presence of vibration or impact.
[0014] In an embodiment, an inertial MEMS system includes: an inertial MEMS device as described above, and a control circuit. The control circuit is electrically coupled to the inertial MEMS device and is configured to: receive an activation signal; compare the activation signal with a first threshold and a second threshold, the second threshold being greater than the first threshold; if the activation signal is greater than the first threshold and less than the second threshold, activate the inertial MEMS device using a low-consumption operation; and if the activation signal is greater than the second threshold, activate the inertial MEMS device using a high-consumption operation.
[0015] In an embodiment, a method for activating an inertial MEMS device includes: receiving an activation signal; comparing the activation signal to a first threshold and a second threshold, the second threshold being greater than the first threshold; activating the inertial MEMS device using a low-consumption operation if the activation signal is greater than the first threshold and less than the second threshold; and activating the inertial MEMS device using a high-consumption operation if the activation signal is greater than the second threshold.
[0016] In an embodiment, a method for manufacturing an inertial MEMS device includes: forming a first structural layer of semiconductor material on a substrate; forming an inertial element in the first structural layer, the inertial element including a movable structure; forming a second structural layer of semiconductor material on the first structural layer; forming a suspension structure in the second structural layer, the suspension structure extending above the movable structure and at a certain distance from the movable structure; and forming a piezoelectric structure on the suspension structure, wherein the suspension structure and the piezoelectric structure form a wake-up element, and the wake-up element is configured to generate an activation signal in the presence of vibration or impact. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] For a better understanding of the invention, some embodiments of the invention will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:
[0018] Figure 1 A block diagram of an inertial MEMS system is shown, the inertial MEMS system comprising an inertial MEMS device;
[0019] Figure 2 is a schematic top view of an embodiment of an inertial MEMS system;
[0020] Figure 3 is a flow chart related to possible operating modes of an inertial MEMS system;
[0021] Figure 4 A and Figure 4 B is an embodiment of an inertial MEMS device respectively along Figure 5 The cross section is taken by the section lines AA and BB;
[0022] Figure 5 yes Figure 4 A and Figure 4 B is a top plan view of a possible layout of an inertial MEMS device;
[0023] Figure 6 yes Figure 4 A and Figure 4 B is a top plan view of different possible layouts of an inertial MEMS device;
[0024] 7A to 15A is Figure 5 The successive manufacturing steps of the inertial MEMS device pass through the semiconductor wafer similar to Figure 4 A cross section; and
[0025] FIG. 7B to FIG. 15B is Figure 5 The successive manufacturing steps of inertial MEMS devices pass through 7A to 15A The semiconductor wafer is similar to Figure 4 The cross section of B, where 7A to 15A and FIG. 7B to FIG. 15B The same reference numerals (7-15) are associated with the same manufacturing steps. DETAILED DESCRIPTION
[0026] The following description refers to the illustrated arrangement; therefore, expressions such as "above," "below," "upper," "lower," "right," "left," etc. relate to the drawings and should not be interpreted in a limiting manner.
[0027] Figure 1 An inertial micro-electromechanical system (MEMS) system 1 is shown, the MEMS system 1 comprising an inertial MEMS device 2 and a control circuit 3 , which is implemented as an application specific integrated circuit (ASIC) comprising circuitry for controlling the operation of the inertial MEMS device 2 .
[0028] The inertial MEMS system 1 is, for example, enclosed in a housing 5 and further comprises a power supply circuit 6 , such as a rechargeable battery, which may be enclosed in the housing 5 or outside.
[0029] The control circuit 3 receives a signal sn, which is typically a movement signal, from the inertial MEMS device 2 and sends a power supply and a control quantity (eg, a voltage P) to the inertial MEMS device 2 .
[0030] The inertial MEMS device 2 incorporates a wake-up element (such as Figure 2 The reference numeral 10 is shown.
[0031] Specifically, refer to Figure 2 The inertial MEMS device 2 here comprises a movable mass 9 and a wake-up element, which is indicated by reference numeral 10 and covers the movable mass 9 .
[0032] The inertial MEMS device 2 is electrically coupled to the control circuit 3 in a manner known per se, for example by means of a first conductive track 11A, a first contact pad 12A and a first conducting wire 13A, for exchanging electrical quantities (power supply, movement signal sn).
[0033] As discussed in detail below, the wake-up element 10 is here formed by a suspended structure, such as a membrane or a cantilever, carrying a piezoelectric structure.
[0034] The piezoelectric structure is electrically coupled to the control circuit 3 , for example by means of one or more second conductive tracks 11B, one or more second contact pads 12B and one or more second conductive lines 13B, and provides a wake-up signal, here a wake-up signal a1 .
[0035] The wake-up element 10 is a piezoelectric structure arranged on a membrane or cantilever, requiring no power supply and capable of generating an output current when subjected to shock, acceleration or other movement; this current can be sensed and causes the inertial MEMS system 1 to activate.
[0036] Specifically, Figure 3 As shown in the flowchart of FIG. 20 , activation may occur according to two activation modes, depending on the degree of the sensed environmental change.
[0037] Specifically, in the absence of environmental changes, the inertial MEMS system 1 is in a static state, block 22. In this state, the inertial MEMS device 2 is turned off, it does not receive power supply and the control circuit 3 operates in a minimally active state, with very low consumption. For example, in this state, the inertial MEMS system 1 may consume a current of several nA (nanoamperes) / second.
[0038] When the wakeup element 10 senses movement, acceleration or impact, "yes" is output from block 24 and the wakeup element 10 generates a wakeup signal a1. The wakeup signal a1 (eg, a continuous signal) is provided by the wakeup element 10 to the control circuit 3, which verifies its amplitude.
[0039] If the wake-up signal a1 is lower than the first threshold Th1 , “No” is output from block 26 , and the inertial MEMS system 1 remains in the static state, and the process returns to block 22 .
[0040] If the wake-up signal a1 exceeds the first threshold Th1, “Yes” is output from box 26 and the control circuit 3 wakes up the inertial MEMS system 1, which includes the inertial MEMS device 2 and its own circuits, which are intended to power the inertial MEMS device 2 and process the signal sn provided by the inertial MEMS device 2.
[0041] Specifically, if the wake-up signal a1 is higher than the first threshold Th1, but lower than the second threshold Th2 (where the second threshold is higher than the first threshold Th1), "No" is output from block 28, and the control circuit 3 activates the inertial MEMS device 2 in a low-power (low-frequency and low-consumption) mode, block 30. For example, under this condition, the inertial MEMS device 2 can operate at a sampling frequency of several Hz (e.g., 1.6 Hz), providing relevant measurement signal samples at such a frequency. In this case, for example, the inertial MEMS system 1 can have a total consumption of the order of hundreds of nA (nanoamperes) / second.
[0042] Under this operating condition, the accuracy of the movement information provided by the inertial MEMS system 1 is not high, but may be sufficient for some low-demand applications (low-power operating condition).
[0043] Furthermore, under this operating condition, the control circuit 3 continues to monitor the wake-up signal a1. If the signal a1 remains below the first threshold Th1, a "No" is output from block 32, and after a period of time, the control circuit 3 stops powering the inertial MEMS device 2 and returns to the static state of block 22.
[0044] On the contrary, if the wake-up signal a1 is higher than the first threshold value Th1, “Yes” is output from box 32 to verify whether the wake-up signal a1 has become higher than the second threshold value Th2, box 33. If not, “No” is output from box 33, the inertial MEMS system 1 remains in the low power mode, and returns to box 30. If it becomes higher than the second threshold value Th2, “Yes” is output from box 33, and the control circuit 3 causes the inertial MEMS system 1 to operate in the high power (high frequency, high consumption) operating mode, box 34.
[0045] Similarly, returning to box 28 , if the wake-up signal a1 is higher than the second threshold Th2 , “Yes” is output from box 28 , and the control circuit 3 activates the inertial MEMS device 2 so that it operates in a high power (high frequency, high consumption) mode, box 34 .
[0046] For example, in high power mode (block 34), the inertial MEMS device 2 may operate at a sampling frequency exceeding 1500 Hz, providing relative signal samples sn to the control circuit 3. In this case, for example, the inertial MEMS system 1 may have a total consumption of the order of tens of μA (microamperes) / second.
[0047] As long as the wake-up signal a1 provided by the wake-up element 10 remains above the second threshold Th2 and / or as long as the control circuit 3 receives the movement signal sn (the movement signal sn is greater than the movement threshold), the inertial MEMS system 1 remains in the high-power operating mode (block 34). In this case, the control circuit 3 stops supplying power to the inertial MEMS device 2 and returns the inertial MEMS system 1 to the static state, returning to block 22. Obviously, the control circuit 3 may provide more complex logic and verification for activating the high-power operating mode to take into account specific functions and / or specific applications.
[0048] Figure 4 A and Figure 4 B shows a possible implementation of an inertial MEMS device 2 incorporating a wake-up element 10. It should be noted that for a better understanding of the structure and manufacturing process, Figure 4 A and Figure 4 B (and the following 7A to 15A and FIG. 7B to FIG. 15B ) shows two different regions of the inertial MEMS device 2 side by side, as shown by Figure 5 As indicated by arrows AA and BB.
[0049] Specifically, Figure 4 A and Figure 4 B and Figure 5 Referring to the inertial MEMS device 2 , the inertial MEMS device 2 comprises an inertial sensor of the capacitive type, here a three-axis accelerometer 35 .
[0050] The three-axis accelerometer 35 comprises a first sensing portion 40, a second sensing portion 41 and a third sensing portion 42. The sensing portions 40-42 comprise a movable structure having a substantially planar extension parallel to a plane XY of a Cartesian reference system XYZ.
[0051] Specifically, in Figure 4 A and Figure 4 In embodiment B, the first sensing unit 40 is used to sense oscillations along the first horizontal axis X of the Cartesian reference system XYZ; the second sensing unit 41 is used to sense oscillations along the second horizontal axis Y of the Cartesian reference system XYZ; and the third sensing unit 42 is used to sense oscillations along the vertical axis Z of the Cartesian reference system XYZ.
[0052] Specifically, Figure 4 A. Figure 4 The inertial MEMS device 2 of B is formed in a tube die 45 of a semiconductor material, and the inertial MEMS device 2 includes: a substrate 50 made of, for example, single crystal silicon; an insulating layer 51 covering the substrate 50, the insulating layer 51 being formed of, for example, a silicon oxide layer; a conductive structure made of, for example, polycrystalline silicon, covering the insulating layer 51 and forming a conductive region 52A (for example Figure 2 conductive tracks 11A, 11B) and a second fixed electrode (here the lower electrode 52B of the third sensing portion 42 is visible); a first structural layer 53, for example made of polycrystalline silicon, the first structural layer 53 covers the insulating layer 51 and the conductive structures 52A and 52B (it can be electrically connected to the conductive region 52A, or capacitively coupled to the lower electrode 52B); a second structural layer 54, for example made of polycrystalline silicon, the second structural layer 54 covers the first structural layer 53 and is mechanically and electrically coupled in some areas; a piezoelectric stack 56, the piezoelectric stack 56 covers the second structural layer 54; and a cover 55, for example made of single crystal silicon, the cover 55 covers and is attached to the second structural layer 54.
[0053] exist Figure 4 A. Figure 4 In the embodiment of B, the first structural layer 53 has a greater thickness than the second structural layer 54. For example, the first structural layer 53 can have a thickness included between 2 μm and 80 μm, and the second structural layer 54 can have a thickness that is differentiated according to the region and included between 1 μm and 2 μm. In general, the second structural layer 54 can have a widely variable thickness, and depending on the application, the thickness is included between 0.5 μm-1 μm and 80 μm.
[0054] also, Figure 4 A. Figure 4 The inertial MEMS device 2 of B includes a dielectric region 58, which is arranged between the insulating layer 51 and the first structural layer 53; an electrical connection region 59, for example, made of a metal such as AlCu (aluminum copper), which is arranged above the second structural layer 54 for forming, for example, Figure 4 A. Figure 4 B; and a bonding area 68 of an adhesive material (such as glass frit), the bonding area 68 being arranged between the cover 55 and the second structural layer 54.
[0055] Specifically, the first and second structural layers 53 , 54 are patterned and locally thinned to define the movable and fixed structures (movable mass, electrodes, suspension springs) of the three-axis accelerometer and to electrically separate portions of the die 45 .
[0056] The inertial MEMS device 2 therefore includes a structure having at least three thicknesses, and precisely includes a structure having a first thickness, the first thickness being equal to the thickness of the first structural layer 53; a structure having a second thickness, the second thickness being equal to the sum of the thickness of the first structural layer 53 and the thickness of the second structural layer 54; and a structure having a third thickness, the third thickness being less than the thickness of the second structural layer 54 due to partial removal of the thickness of the second structural layer 54, as described in detail below.
[0057] For example, in Figure 4 A. Figure 4 In the embodiment shown in B, the first sensing portion 40 and the second sensing portion 41 have a first movable electrode 60A and a first fixed electrode 60B formed only by the first structural layer 53 and therefore having a first thickness; the third sensing portion 42 has a second movable mass block 44 (forming a second movable electrode), and the second movable mass block 44 is formed by two structural layers 53, 54 in the portion shown and therefore has a second thickness; and the cantilever 57 extends above the first sensing portion 40 and the second sensing portion 41 and is formed by a locally thinned second structural layer 54, and therefore has a third thickness.
[0058] exist Figure 4 A. Figure 4 B, a portion of the suspended mass 60C is also visible, integrated with one end of the cantilever 57, formed by the first and second structural layers 53 and thus having a first thickness. Figure 5 As can be seen in FIG. 6 , the suspended mass 60C is arranged here transversely to the second sensing portion 40 , 41 .
[0059] The piezoelectric stack 56 extends over the cantilever 57 and utilizes the cantilever 57 to form Figure 2 Awakening element 10. In a manner not shown, an insulating layer extends between piezoelectric stack 56 and cantilever 57, electrically insulating them.
[0060] The first fixed electrodes 60B are directly and electrically connected to the corresponding conductive regions 52A via the supporting and connecting portions 62 , and face the corresponding first movable electrodes 60A.
[0061] Specifically, the first movable electrode 60A and the first fixed electrode 60B face each other at facing surfaces extending in the thickness direction of the first structure layer 53 (perpendicular to the extension plane XY of the movable structure of the sensing portion 40 - 42 ).
[0062] The second movable mass 44 covers and is capacitively coupled to the lower electrode 52B in a direction perpendicular to the extension plane of the three-axis accelerometer 35 .
[0063] The cantilever 57 is suspended on the first structural layer 53 , and more precisely, in the present embodiment, extends above the first sensing portion 40 and the second sensing portion 41 .
[0064] Specifically, here, the cantilever 57 is fixed at the first end (at the Figure 4 A) and has a second end (on the right side) integral with the suspended mass 60C. Figure 4 A, left side). In this way, the cantilever 57 has a high sensitivity.
[0065] The piezoelectric stack 56 includes a lower electrode region 63 formed from a first conductive layer(s) ; a piezoelectric region 64 of piezoelectric material; and an upper electrode region 65 formed from a second conductive layer(s) .
[0066] For example, the lower electrode region 63 may be formed of a platinum (Pt) layer covering a titanium (Ti) layer, or may include molybdenum (Mo) and / or doped polysilicon; the piezoelectric region 64 may be formed of a material such as PZT (based on lead and titanium zirconate, Pb x [Zr y Ti 1-y ]O3), or may include a layer of aluminum nitride (AlN) or scandium-doped aluminum nitride (AlScN); the upper electrode region 56 may be formed by multiple layers (including indium tin oxide (ITO) and tungsten titanium (TiW) alloy), or by a molybdenum (Mo) or aluminum copper (AlCu) layer.
[0067] Specifically, according to one embodiment, the piezoelectric stack 56 may include an aluminum nitride layer (lower layer) and a molybdenum layer (upper layer) for the lower electrode region 63 (in this case, an insulating layer under the piezoelectric stack 56 is not necessary); a crystalline aluminum nitride (AlN) layer for the piezoelectric region 64; and a molybdenum layer for the upper electrode region 65.
[0068] According to a variant, the piezoelectric region 64 may be formed of potassium sodium niobate (KNN), with a lower electrode 63 and an upper electrode 65 of platinum.
[0069] The layer forming the upper electrode region 64 may extend beyond the piezoelectric stack 56 above the second structural layer 54 to form Figure 2 The conductive track 11B is in direct electrical contact with one of the electrical connection areas 59 .
[0070] A protective dielectric layer 66 , for example made of amorphous aluminum nitride (AlN), covers the piezoelectric stack 56 and is open at the electrical connection region 59 for electrically connecting the lower electrode region 63 and the upper electrode region 65 .
[0071] The cover 55 (in a top view) has a smaller area than the first structural layer 53 and the second structural layer 54 and is rigid with respect to the fixed part, and the fixed part is formed by the first structural layer 53 (the first fixed part 90 is rigid relative to the substrate 50) and the second structural layer 54 (the second fixed part 91 covers the first fixed part 90 and is rigid with respect to the first fixed part 90).
[0072] The cover 55 is rigid with respect to the second fixing part 91 and together with the substrate 50 , the first fixing part 90 and the second fixing part 91 forms a chamber 93 which surrounds the inertial sensor (three-axis accelerometer) 35 and the wake-up element 10 .
[0073] In this embodiment, the chamber 93 is closed; in this way, the inertial sensor (three-axis accelerometer) 35 and the wake-up element 10 are contained in an environment closed to the outside and protected from environmental damage, while being free to move for sensing the movement of the inertial MEMS device 2. In addition, the wake-up element 10 is positioned close to the inertial sensor 35 above and therefore does not require additional space and has high sensitivity.
[0074] Furthermore, since the wake-up element 10 is positioned in close contact with the sensing parts 40 - 42 , it is not damped by the atmosphere within the chamber 93 .
[0075] Possible shapes of the cantilever 57 are as follows: Figure 5 shown.
[0076] Here, the first sensing portion 40 and the second sensing portion 41 (for sensing oscillation along the first horizontal axis X and the second horizontal axis Y, respectively) are arranged side by side along the first horizontal axis X and include a first movable structure 43 integrated with a movable electrode 60A.
[0077] The third sensing portion 42 (for sensing oscillations along the vertical axis Z) is here arranged along the second horizontal axis Y alongside the first sensing portion 40 and the second sensing portion 41 and has a second movable mass 44 forming a second movable electrode.
[0078] The cantilever 57 here has a rectangular shape and extends over the first sensing portion 40 and the second sensing portion 41 .
[0079] Specifically, in Figure 5 In the embodiment, the length of the cantilever 57 (in a direction parallel to the first horizontal axis X) is approximately equal to the sum of the lengths of the first sensing portion 40 and the second sensing portion 41 along the same first horizontal axis X.
[0080] Furthermore, the width of the cantilever 57 (in a direction parallel to the second horizontal axis Y) is smaller than the dimension of the first sensing portion 40 (or the second sensing portion 41 ) along the same second horizontal axis Y, although this is not required.
[0081] As shown, the piezoelectric stack 56 may extend only over the first sensing portion 40 , or may extend along the entire cantilever 57 .
[0082] As an alternative to the content shown, the wake-up element 10 can be arranged only on the first sensing portion 40 or the second sensing portion 41; in addition, the inertial MEMS device 2 can have two wake-up elements 10, one for each sensing axis X, Y, to obtain higher sensitivity, or one for each sensing portion 40, 41. In addition, the wake-up element 10 can also be formed on the third sensing portion 42 or only.
[0083] Figure 6 Different implementations of the inertial MEMS device 2 are shown. Here, the inertial MEMS device 2 comprises, in addition to the inertial sensor (three-axis accelerometer) 35, another inertial sensor, here a gyroscope 36.
[0084] The gyroscope 36 is housed in the chamber 93 together with the three-axis accelerometer 35 and has a movable mass 46 .
[0085] Also in this embodiment, the wake-up element 10 extends over the first and second sensing parts 40 , 41 , between the fixed portion of the die 45 and the suspended mass 60C, but it may extend over only one of the sensing parts 40 , 41 .
[0086] In addition, if the third sensing part 42 and / or the gyroscope 36 or a portion of the third sensing part 42 and / or the gyroscope 36 is formed only in the first structural layer 53, the wake-up element 10 can (also or alternatively) be formed above one or both of the third sensing part 42 and the gyroscope 36 to have more wake-up elements 10 on two or more sensing parts 40-42 and / or the gyroscope 36.
[0087] The inertial MEMS device 2 is completely switched off in the static state.
[0088] When the inertial MEMS device 2 is impacted or moved, the suspended cantilever 57 bends and / or experiences vibrations, causing the piezoelectric stack 56 to deform. As a result, this generates a signal with a small current, which is provided to the control circuit 3. Figure 3 As described, when the current of the signal (ie, its amplitude) exceeds a certain threshold, the control circuit 3 senses the signal and can turn on the inertial MEMS system 1 in a low power or high power state (depending on whether the current exceeds the first threshold Th1 or the second threshold Th2).
[0089] Figure 4 A. Figure 4 The inertial MEMS device 2 of B can be used 7A to 15B The method shown is formed and described below. In these figures, layers and undefined structures are used to help understand Figure 4 A. Figure 4 The same reference numerals as in B are used to indicate the same.
[0090] In detail, Fig. 7A , Figure 7B A sensor wafer 70 of semiconductor material is shown, the sensor wafer 70 comprising a substrate 50 .
[0091] An insulating layer 51 , for example thermally grown or deposited, has been formed on the substrate 50 .
[0092] The conductive structures 52A, 52B have been formed on the insulating layer 51 , for example by deposition of a polysilicon layer and subsequent photolithographic definition.
[0093] A first sacrificial layer 72, for example made of silicon oxide, has been deposited and patterned over the conductive structures 52A, 52B. The first sacrificial layer 72 has been selectively removed over the conductive structure 52A, for example where support and connection parts 62 are to be grown and any other anchoring and electrical and / or mechanical connections to be formed in the first structural layer 53 to the substrate 50 are to be grown as well.
[0094] Then, refer to Fig. 8A , Figure 8BUsing an epitaxial growth process, a first structural layer 53 is grown on the sensor wafer 70. The first structural layer 53 is then grown in a state where the first sacrificial layer 72 has been selectively removed, forming the support and connection parts 62.
[0095] Still reference Fig. 8A , Figure 8B In the case where it is desired to form the first sensing portion 40 and the second sensing portion 41, and any part of the third sensing portion 42 (in which the structure having the first thickness is intended to be formed), the first structure layer 53 is etched, for example, by dry etching. Thus, a first groove 73 is formed, which extends completely through the first structure layer 53. The etching automatically stops on the first sacrificial layer 72 and results in defining the first movable electrode 60A and the first fixed electrode 60B.
[0096] Then, in Fig. 9A , Fig. 9B In the embodiment of the present invention, a second sacrificial layer 74, for example made of tetraethyl orthosilicate (TEOS), is deposited to a thickness comprised, for example, between 0.1 μm and 5 μm. The second sacrificial layer 74 may partially fill the first trench 73, but such filling is not essential.
[0097] The second sacrificial layer 74 is then planarized and selectively removed. Thus, in the case where the second structure layer 54 is desired to be separated from the first structure layer 53 and / or to have a reduced thickness, a sacrificial portion is formed. Specifically, in this step, it is desired to form Figure 4 A. Figure 4 A first sacrificial region 74A and a second sacrificial region 74B of the cantilever 57 of B are formed.
[0098] refer to Fig. 10A , Fig. 10B , the second structure layer 54 is grown on the first structure layer 53 and the second sacrificial layer 74. The second structure layer 54 is epitaxially grown and planarized, for example, by chemical mechanical polishing (CMP), so that in the absence of sacrificial regions 74A and 74B, a complete structure layer having a third thickness is formed. For example, in this embodiment, the third thickness may be included between 1 μm and 2 μm.
[0099] Then, if Fig.11A , Fig. 11B As shown, the piezoelectric stack 56 is formed by depositing and patterning the appropriate layers to form a lower electrode region 63, a piezoelectric region 64, and an upper electrode region 65. In addition, where contacting the electrode regions 63, 65 is desired, a protective dielectric layer 66 is deposited and opened.
[0100] Then, in a manner not shown, the electrical connection region 59, for example made of AlCu, is connected to the electrode regions 63, 65 (relative to Figure 2 The second contact pad 12B) and the corresponding lower layer portions of the first structure layer 53 and the second structure layer 54 (relative to Figure 2 The first contact pad 12A) forms an electrical contact.
[0101] Then, if Fig. 12A , Fig. 12B As shown, the sensor wafer 70 is etched to define a structure formed by only the second structure layer 54 or by two structure layers 53, 54, thereby separating them from the rest of the sensor wafer 70. Specifically, here, the second structure layer 54 and the first structure layer 53 are dry-etched using a mask not shown.
[0102] In detail, in this step, the second movable mass 44 of the third sensitive area 42 is defined and the hole 77 is formed through the second movable mass 44. In the portion shown, the second movable mass 44 thus has a second thickness equal to the sum of the thickness of the first structural layer 53 and the thickness of the second structural layer 54.
[0103] Furthermore, in a manner not shown, the cantilever 57 and any other structures formed only in the second structure layer 54 are defined, with the first structure layer 53 being protected by the sacrificial regions 74A and 74B.
[0104] In this step, the groove 78 (in Figure 5 ) is formed and defines portions of the complete structural layers 53, 54 that are below the electrical connection region 59 (forming the first contact pad 12A) and that are in direct electrical contact with the conductive structures 52A and 52B by means of the conductive region 52A.
[0105] The etching automatically stops on the first sacrificial layer 72 .
[0106] Then, if Fig.13A , Fig. 13B As shown, the first sacrificial layer 72 and the second sacrificial layer 74 , which are exposed to, for example, hydrofluoric acid (HF), are removed, releasing the first movable electrode 60A and the second movable mass 44 .
[0107] Furthermore, the first movable electrode 60A is separated from the corresponding fixed electrode 60B, and the second movable mass 44 is separated from the lower electrode 52B.
[0108] In this step, specifically, the sacrificial region 74A above the first sensing portion 40 is removed, releasing the cantilever 57 .
[0109] Fig.13A , Fig. 13B The sensing portions 40 - 42 are shown fully defined and free.
[0110] exist Fig.14A , Fig. 14B In FIG. 8 , the cover wafer 80 is attached to the sensor wafer 70 by means of the bonding area 68 to form a composite wafer 81. It should be noted that Fig.14A , Fig. 14B The composite wafer 81 is shown relative to 7A to 13B 70, and in particular the area of contact pads 12 (on the right).
[0111] In these drawings, for simplicity, the first movable electrode 60A and the first fixed electrode 60B are indicated by 60 as a whole.
[0112] The cover wafer 80 may have been previously processed to form a recess 82 over the sensing parts 40 - 42 and the wake-up element 10 , allowing sufficient freedom of movement thereof.
[0113] The sensor wafer 70 may therefore be thinned, for example by CMP, to have a desired thickness in the direction of the vertical axis Z.
[0114] Then, in Fig.15A , Fig. 15B In the embodiment, the cover wafer 80 is cut, for example by laser, to open a window 83 above the contact pad 12 ( Figure 2 Only one of the second contact pads 12B is Fig.15A (see ).
[0115] The entire wafer 81 is then cut into Figure 4 A. Figure 4 B and Figure 5 Inertial MEMS device 2.
[0116] In this way, the wake-up element 10 can be easily integrated into the manufacturing process of the MEMS inertial sensor and thus at very low cost by simply modifying the mask and forming the piezoelectric stack 56 .
[0117] Furthermore, as mentioned above, the wake-up element 10 requires no additional space compared to the inertial sensor(s) integrated in the inertial MEMS device 2 , and this can even be used in circuits and devices with very small dimensions.
[0118] Furthermore, the wake-up element 10 is protected from external environmental influences and has a high sensitivity.
[0119] Finally, it is clear that modifications and variations may be made to the inertial MEMS device, the inertial MEMS system and the method of manufacturing described and illustrated without therefore departing from the scope of the present invention as defined in the appended claims.
[0120] For example, in Figure 3In the flowchart of FIG. 3 , the transition from the low power mode operation to the high power mode of operation (block 33 ) may be determined by different conditions.
[0121] The artificial intelligence algorithm may be trained to recognize the type (degree) of movement of the inertial MEMS device and, when rapid movement (e.g., running) is sensed, place the inertial MEMS system 1 into a high-power operating mode, block 34. Conversely, if the algorithm senses movement, but not rapid movement, then, depending on the application, it may place the inertial MEMS system 1 in a low-power mode, return to block 30, and enter the stationary state of block 22 only if there has been no movement for a certain period of time (e.g., between 5 and 30 seconds).
[0122] In addition, as described above, there may be a plurality of cantilevers 57; the cantilever may be arranged only on the first sensing portion 40, the second sensing portion 41, or the third sensing portion 42. A plurality of cantilevers may be provided on the same sensing portion 40-42 or the gyroscope 36, and the cantilever may be a protruding type, attached and integrated to a fixed or movable part only at one end; or may be supported at both ends.
Claims
1. An inertial MEMS device, comprising: an inertial element responsive to movement, the inertial element comprising a movable structure formed in a first structural layer, the first structural layer being made of a semiconductor material; a suspension structure extending above the movable structure at a distance from the movable structure, the suspension structure being formed in a second structural layer made of a semiconductor material; and a piezoelectric structure, the piezoelectric structure being arranged on the suspension structure; The suspension structure and the piezoelectric structure form a wake-up element, and the wake-up element is configured to generate an activation signal in response to vibration or impact. 2 . The inertial MEMS device of claim 1 , wherein the suspended structure is one of a cantilever or a membrane.
3. The inertial MEMS device according to claim 1, further comprising: A substrate made of a semiconductor material; wherein the first structural layer extends over the substrate and comprises a first fixed portion, the first fixed portion being rigid with respect to the substrate; wherein the second structural layer comprises a second fixing portion, and the second fixing portion is in direct contact with the first fixing portion; as well as A cover structure is rigidly coupled to the second fixed part to form a chamber that surrounds the inertial element and the wake-up element. 4 . The inertial MEMS device of claim 1 , wherein the first structure layer is made of silicon, and the second structure layer is made of silicon.
5. The inertial MEMS device of claim 1 , wherein the piezoelectric structure comprises: a piezoelectric stack covering the suspension structure and comprising: a first conductive material providing a first electrode region; a piezoelectric region covering the first electrode region and made of the piezoelectric material; and a second electrode region covering the piezoelectric region and made of a second conductive material providing a second electrode region; At least one of the first electrode region and the second electrode region is coupled to an external connection region.
6. The inertial MEMS device according to claim 1: wherein the first structural layer has a first thickness; wherein the second structural layer has a second thickness, and the second thickness is less than the first thickness; The second structural layer further has a thinned area, the thinned area has a third thickness, the third thickness is less than the second thickness, the thinned area forms the suspension structure and extends at a certain distance from the first structural layer.
7. The inertial MEMS device of claim 1, wherein the inertial element comprises one or more of an accelerometer and a gyroscope.
8. The inertial MEMS device of claim 1, wherein the inertial element is a capacitive type.
9. An inertial MEMS system comprising: The inertial MEMS device according to claim 1; as well as a control circuit electrically coupled to the inertial MEMS device; The control circuit is configured as follows: receiving the activation signal; comparing the activation signal to a first threshold and a second threshold, the second threshold being greater than the first threshold; In response to the activation signal being greater than the first threshold and less than the second threshold, activating the inertial MEMS device from a quiescent state to a low-power operation mode in which the inertial MEMS device is powered off; and In response to the activation signal being greater than the second threshold, the inertial MEMS device is activated to a high consumption operation mode.
10. The inertial MEMS system of claim 9, wherein the control circuit is further configured to: After activation to the low-consumption operating mode: receiving an electrical measurement signal from the inertial element; after an acquisition time, verifying whether one or more of the activation signal and the electrical measurement signal represent a predetermined movement; and when the one or more of the activation signal and the electrical measurement signal do not represent the predetermined movement, deactivating the inertial MEMS device to the static state.
11. A method for activating an inertial MEMS device from a quiescent state, wherein the inertial MEMS device is powered off, the method comprising: receiving an activation signal indicating the presence of vibration or shock, the activation signal being generated by a wake-up element comprising a suspended piezoelectric structure extending above a movable structure of the inertial MEMS device; comparing the activation signal to a first threshold and a second threshold, wherein the second threshold is greater than the first threshold; In response to the activation signal being greater than the first threshold and less than the second threshold, activating the inertial MEMS device from the quiescent state to a low-power mode of operation; and In response to the activation signal being greater than the second threshold, the inertial MEMS device is activated to a high consumption operation mode.
12. A method for manufacturing an inertial MEMS device, comprising: forming a first structure layer on a substrate, wherein the first structure layer is made of a semiconductor material; forming an inertial element in the first structural layer, the inertial element comprising a movable structure; forming a second structure layer on the first structure layer, wherein the second structure layer is made of a semiconductor material; forming a suspension structure in the second structural layer, the suspension structure extending above the movable structure and at a distance from the movable structure; as well as forming a piezoelectric structure on the suspension structure; The suspension structure and the piezoelectric structure form a wake-up element, and the wake-up element is configured to generate an activation signal in response to vibration or impact.
13. The method according to claim 12, further comprising: Before forming the second structure layer, forming a sacrificial region on the movable structure; After forming the piezoelectric structure, defining the second structural layer; as well as The sacrificial area is removed.
14. The method according to claim 12, further comprising: A cover structure is attached to the second structural layer to form a chamber that surrounds the inertial element and the wake-up element.