Micromechanical device with temperature sensor

Abstract

The invention relates to a micromechanical device with a substrate (100), a first functional layer (120) over the substrate and a second functional layer (130) over the first functional layer, wherein an electrically conductive structure (122) for measuring an internal temperature is formed in the first functional layer, wherein a first electrical contact (131) and a second electrical contact (132) are formed in the second functional layer, wherein the first electrical contact and the second electrical contact are electrically connected to the electrically conductive structure.

Description

State of the art

[0001] Inertial sensors for the consumer goods market are usually installed in a mold package. This essentially consists of a carrier circuit board, an evaluation ASIC chip, and a MEMS chip. All components are connected by adhesive layers and protected with a potting compound.

[0002] To compensate for the effects of temperature variations occurring in the sensor, the temperature is typically measured by a temperature sensor integrated into the ASIC. Based on the measured value, a correction value is calculated and used in the data path for compensation.

[0003] If the sensor is mounted on another circuit board with additional components, these can lead to heating (e.g., power ICs), but especially to a temperature gradient across the sensor package. For example, a waste heat-generating component could be placed beneath the sensor, so that the heat flow from bottom to top through the package leads to a temperature drop ( Fig. ). Due to the different thermal conductivities of the components, a stepped temperature profile develops. In particular, the ASIC has a different temperature than the MEMS. Since the correction value for the compensation is now measured at a different location (in the ASIC) than in the MEMS element - where the main temperature-related effects occur - the resulting compensation is not correct. This becomes noticeable in the output signal, for example, as transient or static offset changes that are too large for certain applications, such as dead reckoning. For example, changes in the offset of a yaw rate sensor can occur that are in the range of 0.01..0.1° / s per degree of external temperature change. Object of the invention

[0004] The object of the invention is to create a micromechanical device whose temperature can be measured as directly and reliably as possible. Core and advantages of the invention

[0005] The invention relates to a micromechanical device comprising a substrate, a first functional layer above the substrate and a second functional layer above the first functional layer, wherein an electrically conductive structure for measuring an internal temperature is formed in the first functional layer, wherein a first electrical contact and a second electrical contact are formed in the second functional layer, wherein the first electrical contact and the second electrical contact are electrically conductively connected to the electrically conductive structure.

[0006] The core of the invention is the measurement of the temperature directly in the MEMS element near the substrate. This enables, among other things, the calculation of precise correction values ​​for temperature-dependent behavior of micromechanical structures based at least on this temperature. The temperature sensor in the micromechanical device is manufactured using the same process as the MEMS element itself, making integration very simple. A variant is also proposed that requires virtually no additional surface area and no additional electrical connections.

[0007] The advantage is that the electrically conductive structure is a temperature-dependent resistor. A thermistor is very easy to manufacture, and its resistance is technically simple to determine.

[0008] It is advantageous if the first functional layer or the second functional layer is made of polysilicon. Polysilicon resistors are well known in semiconductor technology and are easy to implement. Polysilicon diodes are also well known. Accordingly, they can be easily integrated into existing micromechanical manufacturing processes using polysilicon layers.

[0009] An advantageous embodiment of the invention provides that the substrate is electrically conductive, the electrically conductive structure is electrically connected to the substrate at one end, and the first electrical contact or the second electrical contact is electrically connected to the substrate. A substrate contact can advantageously be used for this purpose.

[0010] It is particularly advantageous if the micromechanical device has a further substrate with an integrated ASIC, wherein the ASIC is electrically connected to the first electrical contact and the second electrical contact. Advantageously, the ASIC can be used to electrically control and read the electrically conductive structure for temperature measurement, whether it is a diode or a resistor. Advantageously, the ASIC can then determine the temperature of the micromechanical device from this.

[0011] It is particularly advantageous if the substrate and the additional substrate are connected to each other in such a way that they surround a cavity. Advantageously, the additional substrate not only supports the ASIC but also forms a cap for sensitive micromechanical structures in the cavity.

[0012] Particularly advantageously, the micromechanical device is designed as a rotation rate sensor, with a processing unit that is configured to compensate for offsets using the internal temperature. drawing Fig. Figure 1 a shows the temperature distribution in a packaged micromechanical device mounted above a heat source. Fig. Figure 1 b shows a diagram of the temperature profile in a packaged micromechanical device mounted above a heat source. Fig. 2 shows a micromechanical device according to the invention with a temperature sensor in a first embodiment with a resistor in a layer structure. Fig. 3 shows a micromechanical device according to the invention with a temperature sensor in a second embodiment with a current path via a substrate contact. Description of the characters

[0013] Fig. Figure 1a shows the temperature distribution in a packaged micromechanical device mounted above a heat source. It shows a packaged micromechanical device 10 comprising a MEMS chip 11, an ASIC 12, and a component circuit board 15, which are bonded together with adhesive 13. The device is encased in a mold package 14. The micromechanical device 10 is mounted on one side of a circuit board 20 by means of solder joints 25. A heat source 30, for example, a power semiconductor that dissipates thermal energy, is mounted on an opposite side of the circuit board 20. The heat flow 40 also penetrates the micromechanical device 10. The MEMS chip 11 and the ASIC 12 have a relatively high thermal conductivity. The adhesive 13, the mold compound 14, and the component circuit board 15 have a comparatively low thermal conductivity.

[0014] Fig. Figure 1 b shows a diagram of the temperature profile in a packaged micromechanical device mounted above a heat source. Under the influence of radiation from the heat source and due to the aforementioned different thermal conductivities of various parts of the micromechanical device, a stepped temperature distribution forms. In descending order, the temperatures T unten on a bottom side of the component circuit board, T ASIC in ASIC, T MEMS in the MEMS chip and T oben on the top side of the device. To determine the temperature of micromechanical functional elements, it is therefore useful to measure the temperature T MEMS to measure directly in or on the MEMS chip.

[0015] Fig. Figure 2 shows a micromechanical device according to the invention with a temperature sensor in a first exemplary embodiment with a resistor in a layer structure. It shows a schematic and partial view of a device with a substrate 100, in this case a silicon substrate. A dielectric layer 110 made of oxide is arranged thereon. A first functional layer 120, specifically a thin polysilicon layer, is arranged above the dielectric. A second functional layer 130, in this case a thick polysilicon layer, is arranged above the first functional layer.

[0016] In the first functional layer 120, an electrically conductive structure 122 in the form of a conductor track with a temperature-dependent resistance is formed by microstructuring. In the second functional layer 130, a first electrical contact 131 and a second electrical contact 132 are formed by microstructuring. The first electrical contact and the second electrical contact are each electrically connected to one end of the electrically conductive structure. Thus, a temperature sensor is formed as a temperature-variable resistor on the dielectric layer and thus almost directly on the substrate. The resistance can be electrically read out using the first and second electrical contacts, and thus the temperature on the substrate can be determined.

[0017] The temperature sensor essentially consists of only a single conductor track in the first functional layer of the micromechanical device, the wiring layer. The dimensions of the conductor track are selected so that the resistance lies within a suitable range. This can be in the range of 100 Ω to 100 kΩ. Contacts 131, 132 can be connected to an ASIC with bond wires. This provides the possibility of determining the resistance. This can be done, for example, by feeding a current of 100 µA and measuring the required voltage. Alternatively, a PN junction can be used for the further process, which is placed at a suitable location. Its diode characteristic can also be used to determine the temperature. Implementation as a resistor structure, however, can be carried out without changes to the actual MEMS manufacturing process and is therefore more cost-effective.

[0018] Fig.3 shows a micromechanical device according to the invention with a temperature sensor in a second embodiment with a current path via a substrate contact.

[0019] Particularly space-saving integration is possible if the conductor track is located between two contacts (bond pads), one of which is designed as a conventional substrate contact. Typically, several of these contacts are present. A first electrical contact 131 is not led directly to the substrate 100, but is connected at one end to a longer conductor track, which forms the electrically conductive structure 122 and contacts the substrate 100 at another end. A second electrical contact 132 is designed as a conventional substrate contact and is electrically connected directly to the substrate 100 via an underlying region of the first functional layer 120 and through the structured dielectric layer 110. Here, either the temperature measurement via the resistance measurement or the ground connection for the substrate can take place alternately.Since other contacts remain at the correct potential, there is no immediate effect on the sensor.

[0020] The embodiments explained above thus enable a measurement of the internal temperature on the substrate of the micromechanical device. The obtained temperature measurement can then be used as a replacement for the ASIC temperature measurement practiced in the prior art, or as a supplement to it. This makes it possible to compensate for effects caused by unequal MEMS and ASIC temperatures. These can be, for example, sensitivity or offset errors of an acceleration or yaw rate sensor.

[0021] The MEMS temperature value (internal temperature) is particularly suitable for correcting the offset of a yaw rate sensor. This offset is essentially generated by a phase error Δϕ in combination with a quadrature signal Quad. ΔOffset=Δϕ Quad

[0022] Due to the change in temperature, the gas damping in the MEMS element changes, which in turn influences the phase error. Since this relationship is very well known and occurs exclusively in the MEMS element, it is particularly suitable for improved compensation through MEMS temperature measurement. The phase ϕ is calculated according to arctan(Φ)=ωaQ ωs1(1−(ωaωs)2) where ω a , ω s the drive and detection frequency and Q represents the quality of the oscillator.

[0023] Depending on the system, this can be used to adjust the demodulation phase based on the temperature T or to subsequently correct the offset error in connection with the quadrature: ΔOffsetCorrection=Δϕ(TMEMS)Quad List of reference symbols 10 packaged micromechanical devices 11 MEMS chip 12 ASIC 13 glue 14 Mold packaging 15 components circuit board 20 circuit board 25 solder connection 30 Heat source 40 Heat flow 100 substrate 110 dielectric layer 120 first functional layer 122 resistance structure 130 second functional layer 131 first electrical contact 132 second electrical contact 200 electrical current path

Claims

[1] Micromechanical device comprising a substrate (100), a first functional layer (120) over the substrate and a second functional layer (130) over the first functional layer, - wherein an electrically conductive structure (122) for measuring an internal temperature is formed in the first functional layer, - wherein a first electrical contact (131) and a second electrical contact (132) are formed in the second functional layer, - wherein the first electrical contact and the second electrical contact are electrically conductively connected to the electrically conductive structure. [2] Micromechanical device according to claim 1, characterized by that the electrically conductive structure (122) is a temperature-dependent resistor. [3] Micromechanical device according to claim 1 or 2, characterized by that the first functional layer (120) and / or the second functional layer (130) is formed from polysilicon. [4] Micromechanical device according to one of the preceding claims, characterized by that the substrate (100) is electrically conductive, the electrically conductive structure (122) is electrically conductively connected to the substrate at one end and the first electrical contact (131) and / or the second electrical contact (132) is electrically conductively connected to the substrate. [5] Micromechanical device according to one of the preceding claims, characterized by a further substrate having an ASIC integrated thereon, wherein the ASIC is electrically connected to the first electrical contact (131) and the second electrical contact (132). [6] Micromechanical device according to claim 5, characterized by that the substrate (100) and the further substrate are connected to one another in such a way that they surround a cavern. [7] Micromechanical rotation rate sensor according to one of the preceding claims, with a processing unit configured for offset compensation by means of the internal temperature.

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