MICRO-ELECTRO-MECHANICAL SYSTEM

Description

[0001] The invention relates to a micro-electro-mechanical system (MEMS) comprising a sensor device which has a transmitter which is configured to measure a physical quantity, wherein the transmitter is mechanically movable for measuring the physical quantity, wherein the transmitter in a first state exhibits thermal fluctuations corresponding to an effective temperature T1.

[0002] The invention further relates to a method for manufacturing a micro-electro-mechanical system.

[0003] MEMS are components or assemblies whose smallest components are on the order of a few micrometers. A MEMS typically consists of one or more sensors, actuators, and control electronics on a substrate or chip. The sensors in a MEMS are, for example, inertial sensors, such as accelerometers or rotary encoders (an accelerometer according to the state of the art is shown, for example, in CN 102539827 A). These comprise a movable mass (a transducer) which is attached to a frame or mount via a spring element. Such sensors are modeled as harmonic oscillators with a mass m, a spring constant k, a quality factor Q, and a resonant frequency Ω. The position of the movable mass is usually detected capacitively or piezoelectrically.MEMS sensors can operate in a quasi-static or a resonant mode, with the quasi-static mode being more common. In this mode, signals with frequencies below the resonant frequency Ω are measured. To ensure the highest possible resolution of MEMS sensors, highly sensitive detection of the displacement of the moving mass is required. The measurement accuracy, or resolution, of the sensor can be increased, among other things, by reducing the thermal noise (or thermal fluctuations) of the moving mass. One known method for reducing the thermal noise or thermal fluctuations of the moving mass of sensors is the use of cavity optomechanical accelerometers, which incorporate optical resonators. These are shown, for example, in [reference missing]. "Krause, AG, Winger, M., Blasius, TD, Lin, Q., Painter, O.: A high-resolution microchip optomechanical accelerometer. Nature Photonics 6(11), 768-772 (2012 )". However, these sensors require the application of optical resonators, which significantly increases the complexity of the sensor's technical design. Opto-mechanical systems are therefore not practical for use in MEMS sensors.

[0004] The object of the present invention is to alleviate or eliminate the disadvantages of the prior art. The invention therefore aims in particular to create a MEMS in which the measurement accuracy is increased in a simple and practical manner.

[0005] This problem is solved by a MEMS having the features of claim 1 and a method having the features of claim 15. Preferred embodiments are specified in the dependent claims.

[0006] According to the invention, the MEMS has a high-frequency resonator which is mechanically coupled to the sensor device, wherein the high-frequency resonator can interact with the transmitter of the sensor device through the coupling, wherein the high-frequency resonator is designed as a mechanical high-frequency resonator, wherein the micro-electro-mechanical system has an energy converter which is operatively connected to the high-frequency resonator, wherein the energy converter is configured such that the high-frequency resonator can be excited into a first oscillation state by the energy converter, wherein the high-frequency resonator has a transition frequency in the excited first oscillation state, wherein energy can be transferred from the transmitter to the high-frequency resonator through the interaction of the high-frequency resonator oscillating at the transition frequency with the transmitter of the sensor device,that the transmitter has a second state after the energy transfer, in which the transmitter exhibits thermal fluctuations corresponding to an effective temperature T2, which is lower than T1.

[0007] This offers the advantage that thermal fluctuations, or thermal noise, are reduced through the interaction of the high-frequency resonator with the transmitter. The reduction of thermal fluctuations is thus achieved through the interaction of the transmitter with a mechanical vibration system. Unlike opto-mechanical systems, this system can be coupled to a transmitter simply and cost-effectively. Preferably, the first vibration state differs from the second vibration state. In particular, the first vibration state has a different frequency than the second vibration state. The transition frequency, also known as the transfer frequency, is the frequency at which phonons transition from a low-frequency mode, which is present in the transmitter, to a high-frequency mode, which is present in the high-frequency resonator.The transition frequency is specifically chosen to enable energy transfer from the transmitter to the high-frequency resonator. This energy transfer, or phonon transfer, leads to a "cooling" of the transmitter, or in other words, a reduction in thermal fluctuations, which are characterized by an effective temperature. This reduction in thermal fluctuations reduces the noise of the MEMS sensor device and thus increases its measurement accuracy. The transition frequency is preferably different from the transmitter's resonant frequency. The energy converter can utilize a piezoelectric material or piezoelectric thin films for excitation. The piezoelectric material can have a thickness of, for example, 100 nm to 50 µm. The piezoelectric material can be energized via an electrode structure.The high-frequency resonator can also be excited by means of capacitive excitation.

[0008] It is intended that during energy transfer from the transmitter to the high-frequency resonator, phonons are transferred from first modes to second modes, with the first modes being lower in frequency than the second modes, the transmitter possessing the first modes and the high-frequency resonator the second modes. This phonon transfer can reduce the effective temperature of the transmitter.

[0009] The energy converter can be configured to excite the high-frequency resonator into a second vibrational state. In this excited second vibrational state, the high-frequency resonator has a readout frequency, which is preferably different from the transition frequency. The interaction of the high-frequency resonator oscillating at the readout frequency with the transmitter of the sensor device allows for the measurement of the transmitter's deflection relative to the high-frequency resonator. The readout frequency can also be equal to the transition frequency. Exciting the high-frequency resonator into the second vibrational state is preferably an alternative to exciting it into the first vibrational state.The micro-electro-mechanical system is preferably operable in two different operating states. In a first operating state, the high-frequency resonator is excited at the transition frequency. In a second operating state, the high-frequency resonator can be excited at the readout frequency. The first operating state is preferably intended to reduce the thermal fluctuations of the transmitter, and the second operating state is preferably intended to measure the position of the transmitter. In other words, the second operating state is, in particular, a state in which the MEMS can perform a cavity-assisted readout.

[0010] It can be provided that the high-frequency resonator at least partially overlaps the transmitter of the sensor device. This allows for a particularly simple design for the interaction between the high-frequency resonator and the transmitter. Preferably, the high-frequency resonator and the transmitter each have an overlap area over which the high-frequency resonator overlaps with the transmitter. A mechanical connection between the high-frequency resonator and the transmitter can be established through this overlap area. In particular, the high-frequency resonator can make contact with the transmitter at the overlap area.

[0011] It can be provided that the excitation of the high-frequency resonator by the energy converter takes place in a range with a lower limit of essentially at least 10 kHz, preferably 1 MHz, preferably 100 MHz, particularly preferably 1 GHz, and with an upper limit of essentially at most 1000 GHz, preferably 100 GHz, preferably 10 GHz. Advantageously, these frequency ranges are used in numerous sensors employed in a variety of technical fields, giving the MEMS according to the invention a particularly broad range of applications.

[0012] The energy converter can be configured to excite the high-frequency resonator in such a way that acoustic surface waves are generated on a surface of the transmitter by the excitation with the energy converter. Preferably, the acoustic surface waves have a frequency that differs from the resonant frequency of the high-frequency resonator and / or the resonant frequency of the transmitter. Preferably, the acoustic surface waves are generated on that surface of the transmitter which moves mechanically or undergoes a change in position when a physical quantity is measured with the sensor device.Preferably, the excitation of the high-frequency resonator by the energy converter takes place in the second operating state, in which the high-frequency resonator can be excited to the second vibration state (at the readout frequency), such that the acoustic surface waves have a frequency which is equal to the resonance frequency of the high-frequency resonator or equal to the resonance frequency of the measuring transducer.

[0013] The energy converter can be configured to excite the high-frequency resonator in such a way that bulk modes are generated in the transmitter by the excitation with the energy converter. Preferably, the acoustic bulk modes have a frequency that differs from the resonant frequency of the high-frequency resonator and / or the resonant frequency of the transmitter.

[0014] The sensor device may be designed as an inertial sensor. Reducing thermal fluctuations and thermal noise is particularly important for inertial sensors. The inertial sensor may, for example, include an accelerometer, a vibration sensor, a rotation rate sensor, or a gyroscope.

[0015] The sensor device may include an accelerometer with a test mass.

[0016] It is possible to couple the high-frequency resonator with the accelerometer's test mass for vibration transmission. Reducing the thermal noise of the accelerometer's test mass offers the advantage of increased measurement accuracy.

[0017] It is possible for the high-frequency resonator and the test mass to be formed as a single unit, and for the energy converter to be operatively connected to the test mass in such a way that the energy converter excites the test mass at the transition frequency, and bulk modes are generated in the test mass by this excitation. The bulk modes can have a frequency that differs from the resonant frequency of the high-frequency resonator and / or the test mass.

[0018] The sensor device may include a gyroscope.

[0019] The sensor device may include a cantilever for an atomic force microscope. In particular, the transmitter is configured as a cantilever. The sensor device may be configured as a gravimeter.

[0020] The high-frequency resonator can be configured to contact a surface of the sensor device's transmitter. This contact enables a simple and direct energy transfer from the transmitter to the high-frequency resonator, effectively reducing the transmitter's thermal noise.

[0021] It may be designed that the transmitter is set into vibration during measurement at a frequency lower than the crossover frequency. It may also be designed that the transmitter is set into vibration during measurement at a frequency lower than the readout frequency.

[0022] According to the invention, a method for manufacturing the micro-electro-mechanical system is provided, wherein the method comprises the following steps: Providing a substrate; fabricating a first microstructure on the substrate, wherein the first microstructure comprises the sensor device which includes the transmitter configured to measure the physical quantity, wherein the transmitter is mechanically movable for measuring the physical quantity; fabricating a second microstructure on at least a sub-region of the first microstructure, wherein the second microstructure comprises the high-frequency resonator which is mechanically coupled to the sensor device, wherein the coupling allows the high-frequency resonator to interact with the sensor device; providing the energy converter which is arranged on the first or second microstructure or on the substrate, wherein the energy converter is operatively connected to the high-frequency resonator and configured to excite the high-frequency resonator to a first or second vibrational state.wherein the high-frequency resonator has a transition frequency in the first oscillation state, wherein energy from the sensor device can be transferred to the high-frequency resonator through the interaction of the excited high-frequency resonator with the sensor device.

[0023] The interaction of the excited high-frequency resonator occurs particularly with the transmitter of the sensor device. The individual steps of the method according to the invention are carried out using devices and tools commonly used in semiconductor technology, which are known to a person skilled in the art in the field of semiconductor technology.

[0024] The substrate may be designed as a wafer. The wafer is preferably a silicon wafer.

[0025] It is possible for the first and second microstructures to be produced using a photolithography process. Preferably, the first microstructure is also produced using a photolithography process.

[0026] Within the context of this description, the terms "top", "bottom", "horizontal", "vertical" are to be understood as indications of orientation when the micro-electro-mechanical system is arranged in its normal operating position.

[0027] The invention is further explained below with reference to a preferred embodiment, to which it is not, however, limited. The drawings show: Fig. 1 a first embodiment of a MEMS according to the invention; and Fig. 2 a second embodiment of a MEMS according to the invention.

[0028] Fig. 1 Figure 1 shows an embodiment of a MEMS 1 according to the invention, comprising a sensor device 2 which includes a transmitter 3 configured to measure a physical quantity. The transmitter 3 is mechanically movable for measuring the physical quantity, and in a first state, the transmitter 3 exhibits thermal fluctuations corresponding to an effective temperature T1. In the illustrated embodiment, the transmitter 3 is a diaphragm.

[0029] The MEMS 1 comprises a high-frequency resonator 4, which is mechanically coupled to the sensor device 2, whereby the coupling allows the high-frequency resonator 4 to interact with the transmitter 3 of the sensor device 2. The high-frequency resonator 4 is designed as a mechanical high-frequency resonator 4. In the illustrated embodiment, the high-frequency resonator 4 is formed by Bragg mirrors 5, between which surface acoustic waves 6 are generated, wherein these surface acoustic waves 6 are generated on the surface of the transmitter 3 (the diaphragm).

[0030] The MEMS 1 has an energy converter 7 which is operatively connected to the high-frequency resonator 4 and is configured to excite the high-frequency resonator 4 into a first oscillation state, wherein the high-frequency resonator 4 has a transition frequency in the excited first oscillation state. In the illustrated embodiment, the energy converter 7 is an interdigital transducer.

[0031] Through the interaction of the high-frequency resonator 4, oscillating at the transition frequency, with the transmitter 3 of the sensor device 2, energy can be transferred from the transmitter 3 to the high-frequency resonator 4 in such a way that, after the energy transfer, the transmitter 3 exhibits a second state in which it displays thermal fluctuations corresponding to an effective temperature T2. The temperature T2 is lower than T1. Thus, due to the interaction with the high-frequency resonator 4, the transmitter 3 exhibits reduced thermal fluctuations and therefore reduced thermal noise.

[0032] During the energy transfer from the measuring transmitter 3 to the high-frequency resonator 4, phonons are transferred from first modes (at the measuring transmitter) to second modes (at the high-frequency resonator), with the first modes being lower frequency than the second modes.

[0033] Fig. 2Figure 1 shows a second embodiment of a MEMS 1 according to the invention, wherein the transmitter 3 is designed as an oscillating beam. The transmitter 3 is made of a piezoelectric material, and the energy converter 7 comprises two electrodes, one electrode being arranged vertically above and the other vertically below the transmitter 3. The electrodes of the transmitter 7 are configured to excite the piezoelectric material to oscillation. In the illustrated embodiment, bulk modes are formed in the transmitter 3. The lower electrode of the energy converter is mounted on a substrate 8.

[0034] In this embodiment, the high-frequency resonator 4 and the transmitter 3 are formed in one piece, and the energy converter 7 is operatively connected to the transmitter 3 in such a way that the energy converter 7 excites the transmitter 3, whereby bulk modes with the transition frequency or the readout frequency are formed in the transmitter 3 by the excitation.

Claims

1. Micro-electro-mechanical system (1) comprising: a sensor device (2) comprising a transducer (3) configured to measure a physical quantity, wherein the transducer (3) is mechanically movable for measuring the physical quantity, wherein the transducer (3) in a first state has thermal fluctuations corresponding to an effective temperature T1, characterized by a high-frequency resonator (4) mechanically coupled to the sensor device (2), wherein the coupling enables the high-frequency resonator (4) to interact with the transducer (3) of the sensor device (2), wherein the high-frequency resonator (4) is realized as a high-frequency mechanical resonator (4), wherein the micro-electro-mechanical system (1) comprises an energy converter (7) which is operationally connected with the high-frequency resonator (4), the energy converter (7) being configured to excite the high-frequency resonator (4) into a first oscillation state by the energy converter (7), the high-frequency resonator (4), when in the excited first oscillation state, having a transition frequency, wherein the high-frequency resonator (4) and the transducer (3) of the sensor device (2) are configured such that, by virtue of the interaction of the high-frequency resonator (4) oscillating at the transition frequency, energy is transmitted using the transducer (3) of the sensor device (2) from the transducer (3) to the high-frequency resonator (4) in such a way that the transducer (3) is, after the energy transfer, in a second state in which the transducer (3) exhibits thermal fluctuations corresponding to an effective temperature T2 lower than T1, wherein during the energy transfer from the measuring transducer (3) to the high-frequency resonator (4), phonons are transferred from first modes to second modes, the first modes having lower frequency than the second modes, wherein the transducer (3) comprises the first modes and the high-frequency resonator (4) comprises the second modes.

2. Micro-electro-mechanical system (1) according to claim 1, wherein the energy converter (7) is configured to excite the high-frequency resonator (4) into a second oscillation state, wherein in the excited second oscillation state the high-frequency resonator (4) comprises a readout frequency which is preferably different from the transition frequency, wherein, by virtue of the interaction of the high-frequency resonator (4) oscillating at the readout frequency with the transducer (3) of the sensor device, the high-frequency resonator (4) is enabled to measure a deflection of the transducer (3).

3. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the high-frequency resonator (4) at least partially overlaps with the transducer (3) of the sensor device (2).

4. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the excitation of the high-frequency resonator (4) by the energy converter (7) is in a range with a lower limit of substantially at least 10 kHz, preferably 1 MHz, preferably 100 MHz, more preferably 1 GHz, and with an upper limit of substantially at most 1000 GHz, preferably 100 GHz, preferably 10 GHz.

5. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the energy converter (7) is configured to excite the high-frequency resonator (4) in such a way that acoustic surface waves are formed on a surface of the measuring transducer (3) as a result of the excitation by the energy converter (7).

6. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the energy converter (7) is configured to excite the high-frequency resonator (4) in such a way that bulk modes are formed in the measuring transducer (3) by the excitation with the energy converter (7).

7. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the sensor device (2) is realized as an inertial sensor.

8. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the sensor device (2) comprises an acceleration sensor having a test mass, wherein preferably the high-frequency resonator (4) is coupled to the test mass of the acceleration sensor for vibration transmission, wherein preferably the high-frequency resonator (4) and the test mass are formed in one piece and the energy converter (7) is operatively connected to the test mass such that the energy converter (7) excites the test mass at the transition frequency and bulk modes are formed in the test mass as a result of the excitation.

9. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the sensor device (2) comprises a gyroscope.

10. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the sensor device (2) comprises a cantilever for an atomic force microscope.

11. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the high-frequency resonator (4) contacts a surface of the transducer (3) of the sensor device (2).

12. Micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the transducer (3) is caused to oscillate during measurement, at oscillations lower than the transition frequency.

13. Method for manufacturing a micro-electro-mechanical system (1) according to any one of the preceding claims, wherein the method comprises the steps of: - providing a substrate; - producing a first microstructure on the substrate, the first microstructure including the sensor device (2) comprising the transducer (3) configured to measure the physical quantity, wherein the transducer (3) is mechanically movable for measuring the physical quantity, - producing a second microstructure on at least a portion of the first microstructure, wherein the second microstructure comprises the high-frequency resonator (4), which is mechanically coupled to the sensor device (2), wherein the coupling enables the high-frequency resonator (4) to interact with the sensor device (2), - providing the energy converter (7), which is arranged on the first or second microstructure or on the substrate, wherein the energy converter (7) is operatively connected to the high-frequency resonator (4) and is configured to excite the high-frequency resonator (4) into a first or second oscillation state, the high-frequency resonator (4) having a cut-off frequency in the first oscillation state, wherein the interaction of the excited high-frequency resonator (4) with the sensor device (2) enables transferring energy from the sensor device (2) to the high-frequency resonator (4).

14. Method according to claim 13, wherein the substrate is realized as a wafer.

15. Method according to claim 13 or 14, wherein the first and second microstructures are produced using a photolithography process.