Patent Application
20240182293
The invention relates to a micro-electromechanical system (MEMS) comprising a sensor device comprising a measuring deformer configured to measure a physical quantity, wherein the measuring deformer is mechanically movable to measure the physical quantity, wherein the measuring deformer in a first state exhibits thermal fluctuations corresponding to an effective temperature T1.
The invention further relates to a method for manufacturing a micro-electromechanical system.
MEMS are components or assemblies whose smallest components exhibit sizes in the range of a few micrometres. A MEMS typically consists of one or more sensors, actuators and an electronic control system on a substrate or chip. The sensors of a MEMS are, for example, inertial sensors, e.g., acceleration or rotation sensors. These comprise a movable mass (a measuring deformer) attached to a frame or mount via an elastic element. These kinds of sensors are modelled as a harmonic vibrator, with a mass m, a spring constant k, a quality factor Q and a resonant frequency Ω. The position of the movable mass is typically captured capacitively or by piezoelectric means. MEMS sensors can be operated in a quasistatic or a resonant regime, wherein the quasistatic regime is used more frequently. In this regime, signals are measured that have a frequency below the resonant frequency Ω. In order to guarantee a highest possible resolution of MEMS sensors, it is necessary for a detection of the deflection of the movable mass to be as sensitive as possible. The measurement accuracy or resolution of the sensor can be increased, inter alia, by reducing the thermal noise (or thermal fluctuations) of the movable mass. So-called cavity optomechanical accelerometers, which comprise optical resonators, constitute a known option for reducing the thermal noise or the thermal fluctuations of the movable mass of sensors. These are shown, for example, in “Krause, A. G., Winger, M., Blasius, T. D., Lin, Q., Painter, O.: A high-resolution microchip optomechanical accelerometer. Nature Photonics 6(11), 768-772 (2012)”. With these sensors, however, it is necessary to mount optical resonators on the sensors, which leads to a significant increase in the complexity of the technical design of the sensor. Opto-mechanical systems are thus not feasible for use with MEMS sensors.
The object of the present invention is to attenuate or eliminate the drawbacks of the prior art. The aim of the invention is thus in particular to provide a MEMS with which measurement accuracy is increased in a simple and feasible manner.
This object is achieved by a MEMS with the features of claim 1 and a method with the features of claim 15. Preferred embodiments are indicated in the dependent claims.
According to the invention, the MEMS includes a high-frequency resonator that is mechanically coupled to the sensor device, wherein by means of the coupling the high-frequency resonator can interact with the measuring deformer of the sensor device, wherein the high-frequency resonator is configured as a mechanical high-frequency resonator, wherein the micro-electromechanical system includes an energy converter that is operatively connected to the high-frequency resonator, wherein the energy converter is configured so that the high-frequency resonator can be excited into a first vibration state by the energy converter, wherein the high-frequency resonator has a transition frequency in the excited first vibration state, wherein, through the interaction of the high-frequency resonator vibrating at the transition frequency with the measuring deformer of the sensor device, energy can be transferred from the measuring deformer to the high-frequency resonator in such a manner that the measuring deformer after the energy transfer exhibits a second state in which the measuring deformer exhibits thermal fluctuations corresponding to an effective temperature T2 lower than T1.
This yields the advantage that thermal fluctuations or thermal noise is reduced by the interaction of the high-frequency resonator with the measuring deformer. The reduction of thermal fluctuations accordingly occurs through the interaction of the measuring deformer with a mechanical vibration system. In contrast to opto-mechanical systems, the latter can be coupled to a measuring deformer easily and inexpensively. Preferably, the first vibration state is different from the second vibration state. In particular, the first vibration state has a different frequency than the second vibration state. The transition frequency can also be called transfer frequency and is the frequency at which phonons transition from a low-frequency mode exhibited by the measuring deformer to a high-frequency mode exhibited by the high-frequency resonator. The transition frequency is in particular chosen in such a manner that there occurs a transfer of energy from the measuring deformer to the high-frequency resonator. The energy transfer or phonon transfer leads to a “cooling” of the measuring deformer, or in other words, to a reduction in thermal fluctuations, which are characterised by an effective temperature. By reducing the thermal fluctuations, the noise of the sensor device of the MEMS is reduced so that its measurement accuracy is increased. The transition frequency is preferably different from the resonant frequency of the measuring deformer. The energy converter can include 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 supplied with energy by means of an electrode structure. The high-frequency resonator can also be excited by means of capacitive excitation.
It can be provided that, during the energy transfer from the measuring deformer to the high-frequency resonator, phonons are transferred from first modes to second modes, wherein the first modes have a lower frequency than the second modes, wherein the measuring deformer exhibits the first modes and the high-frequency resonator exhibits the second modes. By means of the phonon transfer, it is possible to achieve a reduction of the effective temperature of the measuring deformer.
It can be provided that the energy converter is configured so that the high-frequency resonator can be excited by the energy converter into a second vibration state, wherein the high-frequency resonator in the excited second vibration state has a readout frequency that is preferably different from the transition frequency, wherein, through the interaction of the high-frequency resonator vibrating at the readout frequency with the measuring deformer of the sensor device, a deflection of the measuring deformer can be measured with the high-frequency resonator. The readout frequency can also be equal to the transition frequency. The excitation of the high-frequency resonator into the second vibration state is preferably an alternative to the excitation of the high-frequency resonator into the first vibration state. The micro-electromechanical system can preferably be operated in two different operating states, wherein in a first operating state the excitation of the high-frequency resonator occurs at the transition frequency. In a second operating state, the excitation of the high-frequency resonator can occur at the readout frequency. The first operating state is preferably provided for reducing the thermal fluctuations of the measuring deformer and the second operating state is preferably provided for measuring the position of the measuring deformer. In other words, the second operating state is in particular a state in which the MEMS can carry out a cavity-assisted readout.
It can be provided that the high-frequency resonator at least partially overlaps with the measuring deformer of the sensor device. The interaction between the high-frequency resonator and the measuring deformer can thereby be achieved with a particularly simple design.
Preferably, the high-frequency resonator and the measuring deformer respectively include an overlap area over which the high-frequency resonator overlaps with the measuring deformer. A mechanical connection between the high-frequency resonator and the measuring deformer can be produced through the overlap area. In particular, the high-frequency resonator can contact the measuring deformer at the overlap area.
It can be provided that the excitation of the high-frequency resonator by the energy converter occurs in a range with a lower limit value of essentially at least 10 kHz, preferably 1 MHz, more preferably 100 MHz, particularly preferably 1 GHz, and with an upper limit value of essentially at most 1000 GHz, preferably 100 GHz, more preferably 10 GHz. Advantageously, these frequency ranges are employed in numerous sensors that are used in a variety of technical fields, whereby the MEMS according to the invention has a particularly broad range of application.
It can be provided that the energy converter is configured to excite the high-frequency resonator in such a manner that surface-acoustic waves are formed on a surface of the measuring deformer by means of the excitation with the energy converter. Preferably, the surface-acoustic waves have a frequency that is different from the resonant frequency of the high-frequency resonator and/or the resonant frequency of the measuring deformer. Preferably, the surface-acoustic waves are formed on the surface of the measuring deformer that 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 occurs in the second operating state, in which the high-frequency resonator can be excited into the second vibration state (at the readout frequency), in such a manner that the surface-acoustic waves have a frequency equal to the resonant frequency of the high-frequency resonator or equal to the resonant frequency of the measuring deformer.
It can be provided that the energy converter is configured to excite the high-frequency resonator in such a manner that bulk modes are formed in the measuring deformer by means of the excitation with the energy converter. Preferably, the bulk modes have a frequency that is different from the resonant frequency of the high-frequency resonator and/or the resonant frequency of the measuring deformer.
It can be provided that the sensor device is configured as an inertial sensor. The reduction of thermal fluctuations or thermal noise is particularly important for inertial sensors. The inertial sensor can comprise, for example, an accelerometer, a vibration sensor, a rotation-rate sensor or a gyroscope.
It can be provided that the sensor device comprises an accelerometer with a test mass.
It can be provided that the high-frequency resonator is coupled to the test mass of the accelerometer to transmit vibrations. Reducing the thermal noise of the test mass of the accelerometer yields the advantage that the measurement accuracy of the accelerometer can be increased.
It can be provided that the high-frequency resonator and the test mass are configured as one piece and the energy converter is operatively connected to the test mass in such a manner that the energy converter excites the test mass at the transition frequency and bulk modes are formed in the test mass by the excitation. The bulk modes can have a frequency that is different from the resonant frequency of the high-frequency resonator and/or the test mass.
It can be provided that the sensor device comprises a gyroscope.
It can be provided that the sensor device comprises a cantilever for an atomic force microscope. In particular, the measuring deformer is configured as a cantilever. The sensor device can be configured as a gravimeter.
It can be provided that the high-frequency resonator contacts a surface of the measuring deformer of the sensor device. An easy and direct transmission of energy from the measuring deformer to the high-frequency resonator can occur by means of the contact in order to efficiently reduce the thermal noise of the measuring deformer.
It can be provided that the measuring deformer is set into a vibration during measurement that is lower than the transition frequency. It can also be provided that the measuring deformer is set into a vibration during measurement that is lower than the readout frequency.
According to the invention, a method for manufacturing a micro-electromechanical system is provided, wherein the method comprises the following steps:
The interaction of the excited high-frequency resonator occurs in particular with the measuring deformer of the sensor device. The individual steps of the method according to the invention are performed by means of standard devices and tools in semiconductor technology, which are known to a person skilled in the art in the field of semiconductor technology.
It can be provided that the substrate is configured as a wafer. The wafer is preferably a silicon wafer.
It can be provided that the first and second microstructures are manufactured using a photolithography process. Preferably, the first microstructure is also manufactured using a photolithography process.
In the context of this description, the terms ‘top’, ‘bottom’, ‘horizontal’, ‘vertical’ are to be understood as orientational indications when the micro-electromechanical system is arranged in the normal position of use.
The invention is explained further in the following based on a preferred example embodiment, to which, however, it is not intended to limit the invention. The drawings show:
The MEMS 1 comprises a high-frequency resonator 4 mechanically coupled to the sensor device 2, wherein by means of the coupling the high-frequency resonator 4 can interact with the measuring deformer 3 of the sensor device 2. The high-frequency resonator 4 is configured as a mechanical high-frequency resonator 4. In the example embodiment shown, the high-frequency resonator 4 is formed by Bragg reflectors 5 between which surface-acoustic waves 6 are formed, wherein these surface-acoustic waves 6 are formed on the surface of the measuring deformer 3 (the diaphragm).
The MEMS 1 includes an energy converter 7 that is operatively connected to the high-frequency resonator 4 and is configured to excite the high-frequency resonator 4 into a first vibration state, wherein the high-frequency resonator 4 has a transition frequency in the excited first vibration state. In the example embodiment shown, the energy converter 7 is an interdigital transducer.
By means of the interaction of the high-frequency resonator 4 vibrating at the transition frequency with the measuring deformer 3 of the sensor device 2, energy can be transferred from the measuring deformer 3 to the high-frequency resonator 4 in such a manner that the measuring deformer 3 after the energy transfer exhibits a second state in which the measuring deformer 3 exhibits thermal fluctuations corresponding to an effective temperature T2. The temperature T2 is lower than T1. The measuring deformer 3 thus exhibits lower thermal fluctuations or a reduced thermal noise due to the interaction with the high-frequency resonator 4.
During the energy transfer from the measuring deformer 3 to the high-frequency resonator 4, phonons are transferred from first modes (at the measuring deformer) to second modes (at the high-frequency resonator), wherein the first modes have a lower frequency than the second modes.
In this example embodiment, the high-frequency resonator 4 and the measuring deformer 3 are configured as one piece and the energy converter 7 is operatively connected to the measuring deformer 3 in such a manner that the energy converter 7 excites the measuring deformer 3, wherein bulk modes at the transition frequency or readout frequency are formed in the measuring deformer 3 by the excitation.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 50307/2021 | Apr 2021 | AT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/AT2022/060112 | 4/12/2022 | WO |
