JP2007057287A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device capable of accurate detection of a pressure and a temperature without being influenced by an ambient temperature change. <P>SOLUTION: This surface acoustic wave device wherein a part of semiconductor substrate is formed thinly and surface acoustic wave elements are formed thereon is equipped with the surface acoustic wave elements 20, 21 for exciting different frequencies, oscillation circuits 31, 36 for exciting each element, F/V conversion circuits 32, 37 for converting each oscillation frequency into a voltage and outputting it, a storage device 34 for storing data on the oscillation frequencies at a temperature and a pressure used as a reference and data on a temperature coefficient and a pressure coefficient, comparison circuits 33, 38 for comparing data on the oscillation frequencies and outputting its difference, and an operation circuit 39 for operating and outputting data on a temperature and a pressure at the temperature used as a reference based on data output from the comparison circuits 33, 38 and the data on the temperature coefficient and the pressure coefficient output from the storage device 34, and outputting the result. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave device that detects pressure and temperature.

Conventionally, as shown in Patent Document 1 as a surface acoustic wave device (SAW Device), a piezoelectric thin film is formed on a semiconductor substrate, an IDT (Interdigital Transducer) electrode is provided thereon, and a surface acoustic wave element including the IDT electrode is excited. 2. Description of the Related Art A surface acoustic wave device configured with peripheral circuit elements for performing the above is known.
In general, it is known that a surface acoustic wave changes depending on temperature and stress (pressure). A surface acoustic wave device that detects pressure using this property includes a surface acoustic wave pressure sensor. For example, as shown in Non-Patent Document 1, a pressure sensor is proposed in which a ZnO thin film is formed on a silicon substrate and an IDT electrode is provided thereon. In this type of surface acoustic wave pressure sensor, a surface acoustic wave element is provided on a diaphragm with a thin substrate, and when pressure is applied to the diaphragm, the surface stress changes, and the sound velocity changes. The interval also changes, and as a result, the oscillation frequency (or resonance frequency) changes. Therefore, the pressure can be detected by the change in the oscillation frequency.

Japanese Utility Model Publication No. 3-24719 IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 51, NO. 11, NOVEMBER 2004.

However, such a surface acoustic wave pressure sensor using surface acoustic waves is greatly affected by the ambient temperature, and cannot detect pressure with high accuracy by itself. Therefore, in order to correct the influence of the temperature, thermistor or another IDT electrode is provided in a part other than the diaphragm to detect the temperature and the temperature correction is performed. There was a problem that the temperature could not be corrected accurately.
Some devices detect only pressure, but no surface acoustic wave device detects both pressure and temperature.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a surface acoustic wave device that can detect pressure and temperature with high accuracy without being affected by changes in ambient temperature. is there.

  In order to solve the above problems, a surface acoustic wave device according to the present invention includes a surface acoustic wave element having a piezoelectric thin film and an IDT electrode on a semiconductor substrate, and the semiconductor substrate in a portion where the surface acoustic wave element is formed A surface acoustic wave device having a thin structure, wherein the first surface acoustic wave element and a second elasticity that excites an oscillation frequency different from the oscillation frequency excited from the first surface acoustic wave element. A surface acoustic wave element, a first oscillation circuit for exciting the first surface acoustic wave element, a second oscillation circuit for exciting the second surface acoustic wave element, and the first surface acoustic wave element. A first F / V conversion circuit that converts the oscillation frequency into a voltage and outputs the voltage; a second F / V conversion circuit that converts the oscillation frequency of the second surface acoustic wave element into a voltage; Oscillation frequency at temperature and pressure Data relating to the temperature coefficient and pressure coefficient of each oscillation frequency, data output from the first F / V conversion circuit, and reference temperature stored in the memory device The first comparison circuit that compares the data related to the oscillation frequency at the pressure and outputs the difference, the data output from the second F / V conversion circuit, and the oscillation at the temperature and pressure stored in the storage device A second comparison circuit for comparing frequency reference data and outputting the difference; data output from the first comparison circuit and the second comparison circuit; and a temperature coefficient output from the storage device And a calculation circuit for calculating and outputting the pressure data at the temperature and the reference temperature based on the data relating to the pressure coefficient. And butterflies.

  According to this configuration, an oscillation frequency corresponding to the state of the semiconductor substrate can be obtained from two surface acoustic wave elements, such as when pressure is applied to the thin portion of the semiconductor substrate. These two oscillation frequencies obtained are the frequencies including the elements of temperature and pressure. Using the reference temperature and pressure data stored in the storage device in advance and the respective temperature coefficient and pressure coefficient data, The pressure data at the temperature and the reference temperature can be output from the arithmetic circuit. As described above, the temperature and pressure data can be separated directly from the two frequencies corresponding to the state of the semiconductor substrate, and the pressure and temperature can be accurately detected without being affected by the ambient temperature change. A surface acoustic wave device can be provided.

  In the surface acoustic wave device of the present invention, the first surface acoustic wave element and the second surface acoustic wave element are designed to have different frequencies in the same excitation mode, and each has a frequency of the same excitation mode or a different excitation mode. It is desirable to be excited.

  According to this surface acoustic wave device, the two surface acoustic wave elements are designed to have different frequencies in the same excitation mode, and different oscillation frequencies can be obtained by exciting each in the same excitation mode or different excitation modes. it can. The temperature and pressure data can be separated using these two different oscillation frequencies, and pressure data at the temperature and the reference temperature can be obtained.

  In the surface acoustic wave device of the present invention, the first surface acoustic wave element and the second surface acoustic wave element are designed to have the same frequency in the same excitation mode, and the respective excitation modes have different frequencies. It may be.

  According to this surface acoustic wave device, the two surface acoustic wave elements are designed to have the same frequency in the same excitation mode, and two different oscillation frequencies can be obtained by exciting each in a different excitation mode. Then, using the different oscillation frequencies, the temperature and pressure data can be separated, and the pressure data at the temperature and the reference temperature can be obtained.

  The surface acoustic wave device of the present invention has a structure in which a surface acoustic wave element having a piezoelectric thin film and an IDT electrode is formed on a semiconductor substrate, and the semiconductor substrate in a portion where the surface acoustic wave element is formed is formed thin. A surface acoustic wave device, which is one surface acoustic wave element, a first oscillation circuit that excites the surface acoustic wave element, and an excitation mode that excites the surface acoustic wave element by the first oscillation circuit. A second oscillation circuit for exciting in different excitation modes, a first switch for intermittently selecting the first oscillation circuit or the second oscillation circuit, and an oscillation output from the first oscillation circuit A first F / V conversion circuit that converts the frequency into a voltage and outputs the voltage; a second F / V conversion circuit that converts the oscillation frequency output from the second oscillation circuit into a voltage; Temperature and pressure A first storage device storing data relating to the oscillation frequency and data relating to the temperature coefficient and pressure coefficient of each oscillation frequency; data output from the first F / V conversion circuit; and storing in the storage device A first comparison circuit that compares data relating to the oscillation frequency at the reference temperature and pressure and outputs the difference; a second storage device that temporarily stores the output data of the first comparison circuit; The second switch disposed between the first comparison circuit and the second memory device in conjunction with the first switch, the data output from the second F / V conversion circuit, and the memory A second comparison circuit that compares data on the oscillation frequency at the reference temperature and pressure stored in the apparatus and outputs the difference, and is linked to the first switch before A pressure at a reference temperature based on a second switch arranged at a subsequent stage of the second comparison circuit, data of the second storage device, the second comparison circuit, and the first storage device And an arithmetic circuit for calculating and outputting the data.

  According to this configuration, when a pressure is applied to a thin portion of the semiconductor substrate by intermittently switching between the first oscillation circuit and the second oscillation circuit using one surface acoustic wave element, the semiconductor substrate Two oscillation frequencies corresponding to the state of can be obtained. These obtained oscillation frequencies are frequencies including elements of temperature and pressure. Using the reference temperature and pressure data stored in the storage device in advance and the respective temperature coefficient and pressure coefficient data, the temperature and pressure Pressure data at a reference temperature can be output from the arithmetic circuit. In this way, temperature and pressure data can be separated directly from the oscillation frequency corresponding to the state of the semiconductor substrate, and elasticity that enables accurate pressure and temperature detection without being affected by ambient temperature changes. A surface wave device can be obtained. In addition, pressure and temperature can be detected with a single surface acoustic wave element as described above, and the surface acoustic wave device can be miniaturized.

  In the surface acoustic wave device of the present invention, it is preferable that the semiconductor substrate is provided with a circuit element that forms at least the oscillation circuit with the surface acoustic wave element.

  According to this configuration, since the surface acoustic wave element and the circuit element constituting the oscillation circuit are formed on the semiconductor substrate, it is not necessary to provide a circuit element in another part, and the surface acoustic wave device can be downsized. Can contribute.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.
(First embodiment)

1A and 1B show the structure of a surface acoustic wave device according to the present embodiment. FIG. 1A is a schematic plan view, and FIG. 1B is a schematic cross-sectional view taken along the line AA in FIG.
The surface acoustic wave device 1 includes a semiconductor substrate 10 such as silicon, a circuit layer 11 on which circuit elements and Al wirings are formed, and an insulating layer 12 such as SiO ₂ on the circuit layer 11. A piezoelectric thin film 13 such as a ZnO film is formed on the insulating layer 12.

Further, the semiconductor substrate 10 is etched so that a part of the semiconductor substrate 10 is thin to form thin portions 14 and 15. Thus, the semiconductor substrate 10 has a structure including a diaphragm.
On the piezoelectric thin film 13 corresponding to the thin portions 14 and 15 of the semiconductor substrate 10, IDT electrodes 22, 23, 24 and 25 made mainly of Al are formed, respectively. These IDT electrodes 22, 23, 24, and 25 are formed so that comb-like electrodes are alternately sandwiched. The IDT electrode 22 is an excitation electrode, and the IDT electrode 23 provided at a predetermined interval functions as a reception electrode, and is configured as the first surface acoustic wave element 20 together with the IDT electrodes 22 and 23 and the piezoelectric thin film 13. ing.
Similarly, the IDT electrode 24 is an excitation electrode, and the IDT electrode 25 provided at a predetermined interval functions as a reception electrode, and as the second surface acoustic wave element 21 together with the IDT electrodes 24 and 25 and the piezoelectric thin film 13. It is configured.
Further, the first surface acoustic wave element 20 and the second surface acoustic wave element 21 are designed with different IDT electrode intervals, and are configured to have different oscillation frequencies in the same excitation mode.
The circuit layer 11 formed on the semiconductor substrate 10 detects an oscillation circuit for exciting the first surface acoustic wave element 20 and the second surface acoustic wave element 21, temperature, and pressure. A processing circuit is included.

In the surface acoustic wave device 1 having such a configuration, when the thin portions 14 and 15 of the semiconductor substrate 10 are subjected to pressure P, the thin portions 14 and 15 are distorted, and the surface stress changes to change the speed of sound. The IDT electrode interval of the elements 20 and 21 also changes, and as a result, the oscillation frequency (or resonance frequency) changes. Therefore, by measuring this oscillation frequency, it is possible to detect a change in oscillation frequency as a change in pressure.
The oscillation frequency at this time includes an element of ambient temperature, and it is necessary to obtain a pressure at a reference temperature by separating the element of ambient temperature.
(Temperature and pressure detection principle)

Here, for the understanding of the description, the temperature and pressure detection principles of the surface acoustic wave device according to the present invention will be described.
It is known that the oscillation frequency (or resonance frequency) of a surface acoustic wave changes with temperature and stress (pressure). FIG. 2 shows these relationships in the Rayleigh wave excitation mode, FIG. 2 (a) is an explanatory diagram for explaining an example of the relationship between the oscillation frequency and temperature of the surface acoustic wave device, and FIG. 2 (b) shows the oscillation. It is explanatory drawing explaining an example of the relationship between a frequency and a pressure.
In FIG. 2A, the relationship between the oscillation frequency of the surface acoustic wave element and the temperature is approximated by a straight line and has a specific inclination (temperature coefficient).
In FIG. 2B, the relationship between the oscillation frequency of the surface acoustic wave element and the pressure is approximated by a straight line and has a specific inclination (pressure coefficient).
These inherent slopes (temperature coefficient and pressure coefficient) are determined by the material and thickness of the piezoelectric thin film, and further by the material such as an insulating film formed under the piezoelectric thin film, and each has a specific value.

A difference between the oscillation frequency (or resonance frequency) at the reference temperature and pressure (for example, 25 ° C., 1 atm) and the measured oscillation frequency (or resonance frequency) in the first surface acoustic wave element is Δf ₁ , in the surface acoustic wave device, a primary temperature and pressure (e.g. 25 ° C., 1 atm) when the difference between the oscillation frequency (or resonance frequency) and the measured oscillation frequency (or oscillation frequency) of a Delta] f _2, the following formula ( It can be expressed as 1) and (2).
Δf ₁ = α × ΔT + β × ΔP (1)
Δf ₂ = γ × ΔT + δ × ΔP (2)
α: Temperature coefficient of the oscillation frequency in the first surface acoustic wave device
β: Pressure coefficient of the oscillation frequency in the first surface acoustic wave device
γ: temperature coefficient of the oscillation frequency in the second surface acoustic wave device
δ: Pressure coefficient of the oscillation frequency in the second surface acoustic wave device
ΔT: difference between the reference temperature and the measured temperature
ΔP: difference between the reference pressure and the measured pressure The following equation (3) is obtained from the above equations (1) and (2).

This expression (3) means that there are two different frequencies, and if the reference frequency, temperature coefficient, and pressure coefficient are known, ΔT and ΔP can be obtained.
The surface acoustic wave element excites different frequencies depending on the excitation mode. For example, as shown in the insertion frequency characteristic (conceptual diagram) of FIG. 3, the Rayleigh wave 27 near 300 MHz, the Sezawa wave 28 near 400 MHz, and the Sezawa wave near 500 MHz. A wave (2nd) 29 oscillates. Although not shown, there is also a surface acoustic wave that excites in a higher-order excitation mode.
As the oscillation frequency of the surface acoustic wave element, the surface acoustic waves of these excitation modes also have their own temperature coefficients and pressure coefficients, and the surface acoustic waves in these excitation modes can be used for temperature and pressure detection. Is possible.
(Temperature and pressure detection circuit configuration)

Next, a circuit configuration for temperature and pressure detection will be described with reference to FIG.
The first surface acoustic wave element 20 is connected to the first oscillation circuit 31 and constitutes a feedback circuit. The first oscillation circuit 31 is connected to a first F / V conversion circuit 32 that converts a frequency into a voltage, and the first F / V conversion circuit 32 is connected to a first comparison circuit 33. The first comparison circuit 33 is connected to the storage device 34 and the arithmetic circuit 39.
Similarly, the second surface acoustic wave element 21 is connected to the second oscillation circuit 36 to form a feedback circuit. The second oscillation circuit 36 is connected to a second F / V conversion circuit 37 that converts a frequency into a voltage, and the second F / V conversion circuit 37 is connected to a first comparison circuit 38. The second comparison circuit 38 is connected to the storage device 34 and the arithmetic circuit 39. The storage device 34 is also connected to the arithmetic circuit 39.
The storage device 34 includes data obtained by converting the oscillation frequency at the reference temperature and pressure of the first surface acoustic wave element 20 and the second surface acoustic wave element 21 into voltage values, and temperature coefficients of the respective oscillation frequencies. And pressure coefficient data are stored in advance.

  In the surface acoustic wave device 1 having the above circuit configuration, the first surface acoustic wave element 20 is excited by the first oscillation circuit 31 and the oscillation frequency is transferred from the first oscillation circuit 31 to the first F / V conversion circuit 32. Output. In the first F / V conversion circuit 32, the input frequency is converted into a voltage and output to the first comparison circuit 33. The first comparison circuit 33 reads the reference data (data obtained by converting the oscillation frequency at the reference temperature and pressure into a voltage value) from the storage device 34, compares this data with the input voltage data, The difference data is output to the arithmetic circuit 39.

  On the other hand, the second surface acoustic wave element 21 is excited by the second oscillation circuit 36 and outputs an oscillation frequency from the second oscillation circuit 36 to the second F / V conversion circuit 37. The first surface acoustic wave element 20 and the second surface acoustic wave element 21 have second oscillation circuits 31 and 36 configured to excite Rayleigh waves, respectively, and excite different frequencies. The second F / V conversion circuit 37 converts the input frequency into a voltage and outputs the voltage to the second comparison circuit 38. The second comparison circuit 38 reads the reference data (data obtained by converting the oscillation frequency at the reference temperature and pressure into a voltage value) from the storage device 34, compares this data with the input voltage data, The difference data is output to the arithmetic circuit 39.

Based on the data input from the first and second comparison circuits 33 and 38 and the temperature coefficient and pressure coefficient in each excitation mode read from the storage device 34, the arithmetic circuit 39 calculates ΔT, Data corresponding to ΔP is calculated, added to the reference temperature and pressure data, and temperature data (voltage) V _T and pressure data (voltage) V _P are output from the arithmetic circuit 39. The pressure data V _P does not include a temperature element, and is a pressure value at the reference temperature.

In the above embodiment, the first surface acoustic wave element 20 and the second surface acoustic wave element 21 are designed to have different frequencies in the same excitation mode, and both are used as the excitation modes of the surface acoustic wave element to be used. Although the Rayleigh wave is used, it can be selected in combination with a higher-order excitation mode as shown in Table 1. For example, a Rayleigh wave can be used as the excitation mode of the first surface acoustic wave element 20, and a Sezawa wave can be used as the excitation mode of the second surface acoustic wave element 21.
It is also possible to select and combine higher order excitation modes not listed in Table 1.

As described above, in the surface acoustic wave device 1 of this embodiment, the pressure P is applied to the thin portions 14 and 15 of the semiconductor substrate 10 from the first surface acoustic wave element 20 and the second surface acoustic wave element 21. The frequency corresponding to the state of the semiconductor substrate 10 can be obtained. These obtained oscillation frequencies are frequencies including elements of temperature and pressure, and the temperature and pressure coefficient data stored in the storage device 34 in advance and the temperature coefficient and pressure coefficient data are used to calculate the temperature. The pressure data at the temperature and the reference temperature can be output from the arithmetic circuit 39. In this way, the temperature and pressure data can be directly separated from the frequency corresponding to the state of the semiconductor substrate 10, and the elasticity that enables accurate pressure and temperature detection without being affected by the ambient temperature change. A surface wave device 1 can be provided.
Further, since the first surface acoustic wave element 20 and the second surface acoustic wave element 21 and the circuit elements constituting the circuit shown in FIG. 4 are formed on the semiconductor substrate 10, the surface acoustic wave device 1 can be downsized. Can contribute.
(Modification)

FIG. 5 shows a structure of a modification of the first embodiment, FIG. 5 (a) is a schematic plan view, and FIG. 5 (b) is a schematic cross-sectional view taken along the line BB in FIG. 5 (a). . The same components as those in the first embodiment are denoted by the same reference numerals as those in FIG.
In this modification, the first surface acoustic wave element 40 and the second surface acoustic wave element 41 are configured under the same design conditions such as the IDT electrode interval, and are configured to excite the same frequency in the same excitation mode. Yes.

On the piezoelectric thin film 13 corresponding to the thin portions 14 and 15 of the semiconductor substrate 10, IDT electrodes 42, 43, 44 and 45 made mainly of Al are formed, respectively. These IDT electrodes 42, 43, 44, 45 are formed so that comb-like electrodes are alternately sandwiched. The IDT electrode 42 is an excitation electrode, and the IDT electrode 43 provided at a predetermined interval functions as a reception electrode, and is configured as the first surface acoustic wave element 40 together with the IDT electrodes 42 and 43 and the piezoelectric thin film 13. ing.
Similarly, the IDT electrode 44 is an excitation electrode, and the IDT electrode 45 provided at a predetermined interval functions as a receiving electrode, and as the second surface acoustic wave element 41 together with the IDT electrodes 44 and 45 and the piezoelectric thin film 13. It is configured.

The circuit configuration for temperature and pressure detection is the same as the circuit configuration shown in FIG. 4. In FIG. 4, the first surface acoustic wave element 20 and the second surface acoustic wave element 21 are connected to the first surface acoustic wave element. The element 40 and the second surface acoustic wave element 41 are replaced.
Here, the first surface acoustic wave element 40 and the second surface acoustic wave element 41 are configured to oscillate in different excitation modes. For example, the first surface acoustic wave element 40 includes a Rayleigh wave. The second surface acoustic wave element 41 is excited in the Sezawa wave excitation mode.
Further, the excitation mode to be used can be selected in combination with the excitation modes as shown in Table 2. Furthermore, it is also possible to select and combine higher-order excitation modes not listed in Table 2 for implementation.

The method for detecting the temperature and pressure in the surface acoustic wave device 2 as described above is the same as that described with reference to FIG.
As described above, the surface acoustic wave device 2 according to the present modification is configured such that the pressure P is applied to the thin portions 14 and 15 of the semiconductor substrate 10 from the first surface acoustic wave element 40 and the second surface acoustic wave element 41. For example, a frequency corresponding to the state of the semiconductor substrate 10 can be obtained. These obtained oscillation frequencies are frequencies including elements of temperature and pressure, and the temperature and pressure coefficient data stored in the storage device 34 in advance and the temperature coefficient and pressure coefficient data are used to calculate the temperature. The pressure data at the temperature and the reference temperature can be output from the arithmetic circuit 39. In this way, the temperature and pressure data can be directly separated from the frequency corresponding to the state of the semiconductor substrate 10, and the elasticity that enables accurate pressure and temperature detection without being affected by the ambient temperature change. A surface wave device 2 can be provided.
Since the first surface acoustic wave element 40, the second surface acoustic wave element 41, and the circuit elements constituting the circuit shown in FIG. 4 are formed on the semiconductor substrate 10, the surface acoustic wave device 2 can be downsized. Can contribute.
(Second Embodiment)

Next, a surface acoustic wave device according to the second embodiment will be described.
6A and 6B show the structure of the surface acoustic wave device according to this embodiment. FIG. 6A is a schematic plan view, and FIG. 6B is a schematic cross-sectional view taken along the line CC in FIG.
The surface acoustic wave device 3 includes a semiconductor substrate 50 such as silicon, a circuit layer 51 on which circuit elements and Al wiring are formed, and an insulating layer 52 such as SiO ₂ thereon. A piezoelectric thin film 53 such as a ZnO film is formed on the insulating layer 52.

In addition, the semiconductor substrate 50 is etched so that a part of the semiconductor substrate 50 is thin, so that a thin portion 54 is formed. Thus, the semiconductor substrate 50 has a structure including a diaphragm.
On the piezoelectric thin film 53 corresponding to the thin portion 54 of the semiconductor substrate 50, IDT electrodes 56 and 57 mainly made of Al are formed. These IDT electrodes 56 and 57 are formed so that comb-shaped electrodes are alternately sandwiched. The IDT electrode 56 is an excitation electrode, and the IDT electrode 57 functions as a reception electrode, and is configured as a surface acoustic wave element 55 together with the IDT electrodes 56 and 57 and the piezoelectric thin film 53.
The circuit layer 51 formed on the semiconductor substrate 50 includes an oscillation circuit for exciting the surface acoustic wave element 55, a processing circuit for detecting temperature and pressure, and the like.

  In the surface acoustic wave device 3 having such a configuration, when the thin portion 54 of the semiconductor substrate 50 is subjected to pressure P, the thin portion 54 is distorted, and the surface stress changes to change the speed of sound. The electrode interval also changes, and as a result, the oscillation frequency (or resonance frequency) changes. Therefore, by measuring this oscillation frequency, it is possible to detect a change in oscillation frequency as a change in pressure.

Next, the circuit configuration for temperature and pressure detection will be described with reference to FIG.
The surface acoustic wave element 55 is connected to a switch 70, and the first oscillation circuit 61 or the second oscillation circuit 66 can be selected via the switch 70. The switch 70 is connected to a terminal 71 so that the surface acoustic wave element 55 and the first oscillation circuit 61 are connected to form one feedback circuit. Further, the switch 70 is connected to the terminal 72 so that the surface acoustic wave element 55 and the second oscillation circuit 66 are connected to form the other feedback circuit. The first oscillation circuit 61 and the second oscillation circuit 66 are configured to be able to oscillate the surface acoustic wave element 55 in different excitation modes. The switch 70 is configured to intermittently repeat the connection of the terminals 71 and 72 intermittently.

The first oscillation circuit 61 is connected to a first F / V conversion circuit 62 that converts a frequency into a voltage, and the first F / V conversion circuit 62 is connected to a first comparison circuit 63. The first comparison circuit 63 is connected to the first storage device 64 and is further connected to the second storage device 65 via the switch 73. The switch 73 is linked to the operation of the switch 70. When the switch 70 is connected to the terminal 71, the switch 73 is connected to the terminal 74. When the switch 70 is disconnected from the terminal 71, the switch 73 is also disconnected from the terminal 74. It is configured as follows.
The second storage device 65 is connected to the arithmetic circuit 69.

Similarly, the second oscillation circuit 66 is connected to a second F / V conversion circuit 67 that converts a frequency into a voltage, and the second F / V conversion circuit 67 is connected to a second comparison circuit 68. Yes. The second comparison circuit 68 is connected to the arithmetic circuit 39 via the first storage device 64 and the switch 75. The switch 75 is interlocked with the operation of the switch 70. When the switch 70 is connected to the terminal 72, the switch 75 is connected to the terminal 76. When the switch 70 is disconnected from the terminal 72, the switch 75 is also disconnected from the terminal 76. It is configured as follows. The first storage device 64 is also connected to the arithmetic circuit 69.
In the first storage device 64, data obtained by converting the oscillation frequency at the reference temperature and pressure into voltage values in the two excitation modes excited from the surface acoustic wave element 55, the temperature coefficient of each oscillation frequency, and Pressure coefficient data is stored in advance.

  In the surface acoustic wave device 3 having the above circuit configuration, first, the switch 70 is connected to the terminal 71, and the surface acoustic wave element 55 is excited by the first oscillation circuit 61, and the oscillation frequency is changed from the first oscillation circuit 61 to the first oscillation circuit 61. To the F / V conversion circuit 62. Here, Rayleigh waves are excited in the surface acoustic wave element 55 by the first oscillation circuit 61. The first F / V conversion circuit 62 converts the input frequency into a voltage and outputs it to the first comparison circuit 63. The first comparison circuit 63 reads the reference data (data obtained by converting the oscillation frequency at the reference temperature and pressure into a voltage value) from the first storage device 64, and compares this data with the input voltage data. Then, the difference data is output to the second storage device 65 via the switch 73 linked to the switch 70. Then, the difference data is temporarily stored in the second storage device 65.

  Next, the switch 70 is connected to the terminal 72, and the surface acoustic wave element 55 is excited by the second oscillation circuit 66 and outputs the oscillation frequency from the second oscillation circuit 66 to the second F / V conversion circuit 67. Here, the surface acoustic wave element 55 is excited by a second oscillation circuit 66 with a Sezawa wave. In the second F / V conversion circuit 67, the input frequency is converted into a voltage and output to the second comparison circuit 68. The second comparison circuit 68 reads the reference data (data obtained by converting the oscillation frequency at the reference temperature and pressure into a voltage value) from the first storage device 64, and compares this data with the input voltage data. Then, the difference data is output to the arithmetic circuit 69 via the switch 75 linked to the switch 70.

In the arithmetic circuit 69, based on the data read from the second storage device 65, the data input from the second comparison circuit 68, and the temperature coefficient and pressure coefficient in each excitation mode read from the first storage device 64, Data corresponding to ΔT and ΔP in the above equation (3) is calculated and added to the reference temperature and pressure data, and the temperature data (voltage) V _T and pressure data (voltage) V _P are calculated by the arithmetic circuit 69. Is output from.
The pressure data V _P does not include a temperature element, and is a pressure value at the reference temperature.

In the above embodiment, the Rayleigh wave and the Sezawa wave are excited so that the surface acoustic wave element 55 has different excitation modes. However, the surface acoustic wave element 55 may be selected in combination with other excitation modes as shown in Table 3. For example, the Rayleigh wave and the Sezawa wave 2nd can be used as the excitation mode of the surface acoustic wave element 55.
It is also possible to select and combine higher order excitation modes not listed in Table 3.

As described above, the surface acoustic wave device 3 according to the present embodiment intermittently switches the first oscillation circuit 61 and the second oscillation circuit 66 from one surface acoustic wave element 55, thereby When the pressure P is applied to the thin portion 54, two frequencies corresponding to the state of the semiconductor substrate 50 can be obtained. These obtained oscillation frequencies are frequencies including elements of temperature and pressure. Using the reference temperature and pressure data stored in the storage device in advance and the respective temperature coefficient and pressure coefficient data, The pressure data can be separated, and the pressure data at the temperature and the reference temperature can be output from the arithmetic circuit 69. In this way, the temperature and pressure data can be directly separated from the frequency corresponding to the state of the semiconductor substrate 50, and the elasticity that enables accurate pressure and temperature detection without being affected by the ambient temperature change. The surface wave device 3 can be obtained. In addition, pressure and temperature can be detected by one surface acoustic wave element 55 in this way, and the surface acoustic wave device 3 can be downsized.
Since the surface acoustic wave element 55 and the circuit elements constituting the oscillation circuit and the like are formed on the semiconductor substrate 50, the surface acoustic wave device 3 can be further miniaturized.

In this embodiment, silicon is used as the semiconductor substrate, but a semiconductor substrate such as SiGe or GaAs may be used.
Further, since the surface acoustic wave device of the present invention can detect pressure and temperature, it is expected to be used as a sensor that requires information on pressure and ambient temperature, such as a tire puncture sensor (TPMS).

The structure of the surface acoustic wave device in 1st Embodiment is shown, (a) is a schematic plan view, FIG.1 (b) is a schematic cross section along the AA disconnection of the same figure (a). It is explanatory drawing explaining the relationship between the oscillation frequency of a surface acoustic wave element, temperature, and a pressure, (a) is explanatory drawing explaining an example of the relationship between an oscillation frequency and temperature, FIG.2 (b) is an oscillation frequency and pressure. Explanatory drawing explaining an example of a relationship. The conceptual diagram which shows an example of the insertion frequency characteristic of a surface acoustic wave element. The circuit diagram which shows the circuit structure of the temperature and pressure detection of the surface acoustic wave device in 1st Embodiment. The structure of the surface acoustic wave device of the modification in 1st Embodiment is shown, (a) is a schematic plan view, (b) is a schematic cross section along the BB disconnection of the same figure (a). The structure of the surface acoustic wave device in 2nd Embodiment is shown, (a) is a schematic plan view, (b) is a schematic cross section along the CC disconnection of the same figure (a). The circuit diagram which shows the circuit structure of the temperature and pressure detection of the surface acoustic wave device in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2, 3 ... Surface acoustic wave device, 10 ... Semiconductor substrate, 11 ... Circuit layer, 12 ... Insulating layer, 13 ... Piezoelectric thin film, 14, 15 ... Thin part, 20 ... 1st surface acoustic wave element, 21 ... Second surface acoustic wave element 22, 23, 24, 25 ... IDT electrode, 31 ... first oscillation circuit, 32 ... first F / V conversion circuit, 33 ... first comparison circuit, 34 ... storage device , 36 ... second oscillation circuit, 37 ... second F / V conversion circuit, 38 ... second comparison circuit, 39 ... arithmetic circuit, 40 ... first surface acoustic wave element, 41 ... second elastic surface Wave element, 42, 43, 44, 45 ... IDT electrode, 50 ... Semiconductor substrate, 51 ... Circuit layer, 52 ... Insulating layer, 53 ... Piezoelectric thin film, 54 ... Thin portion, 55 ... Surface acoustic wave element, 56, 57 ... IDT electrode, 61 ... first oscillation circuit, 62 ... first F / V conversion circuit, 63 ... first comparison circuit 64 ... 1st memory | storage device, 66 ... 2nd oscillation circuit, 65 ... 2nd memory | storage device, 67 ... 2nd F / V conversion circuit, 68 ... 2nd comparison circuit, 69 ... arithmetic circuit, 70, 73,75 ... switch, P ... pressure.

Claims (5)

A surface acoustic wave device having a structure in which a surface acoustic wave element having a piezoelectric thin film and an IDT electrode is provided on a semiconductor substrate, and the semiconductor substrate in a portion where the surface acoustic wave element is formed is formed thinly,
A first surface acoustic wave element;
A second surface acoustic wave element in which an oscillation frequency different from the oscillation frequency excited from the first surface acoustic wave element is excited;
A first oscillation circuit for exciting the first surface acoustic wave element;
A second oscillation circuit for exciting the second surface acoustic wave element;
A first F / V conversion circuit that converts an oscillation frequency of the first surface acoustic wave element into a voltage and outputs the voltage;
A second F / V conversion circuit for converting the oscillation frequency of the second surface acoustic wave element into a voltage and outputting the voltage;
A storage device in which data on the oscillation frequency at the reference temperature and pressure and data on the temperature coefficient and pressure coefficient of each oscillation frequency are stored;
A first comparison circuit that compares data output from the first F / V conversion circuit and data relating to an oscillation frequency at a reference temperature and pressure stored in the storage device and outputs the difference;
A second comparison circuit that compares the data output from the second F / V conversion circuit with the reference data relating to the oscillation frequency at the temperature and pressure stored in the storage device and outputs the difference;
Based on the data output from the first comparison circuit and the second comparison circuit and the data on the temperature coefficient and the pressure coefficient output from the storage device, the temperature and the pressure data at the reference temperature are calculated and output. An arithmetic circuit to be
A surface acoustic wave device comprising: The surface acoustic wave device according to claim 1,
The first surface acoustic wave element and the second surface acoustic wave element are designed to have different frequencies in the same excitation mode, and each has the same excitation mode or a different excitation mode frequency. Surface wave device. The surface acoustic wave device according to claim 1,
The surface acoustic wave device according to claim 1, wherein the first surface acoustic wave element and the second surface acoustic wave element are designed to have the same frequency in the same excitation mode, and each has a different excitation mode frequency. A surface acoustic wave device having a structure in which a surface acoustic wave element having a piezoelectric thin film and an IDT electrode is formed on a semiconductor substrate, and the semiconductor substrate in a portion where the surface acoustic wave element is formed is thinly formed,
One surface acoustic wave element;
A first oscillation circuit for exciting the surface acoustic wave element;
A second oscillation circuit for exciting the surface acoustic wave element in an excitation mode different from an excitation mode for exciting the surface acoustic wave element with the first oscillation circuit;
A first switch for intermittently selecting the first oscillation circuit or the second oscillation circuit;
A first F / V conversion circuit for converting an oscillation frequency output from the first oscillation circuit into a voltage and outputting the voltage;
A second F / V conversion circuit for converting an oscillation frequency output from the second oscillation circuit into a voltage and outputting the voltage;
A first storage device storing data relating to oscillation frequencies at a reference temperature and pressure, and data relating to temperature coefficients and pressure coefficients of the respective oscillation frequencies;
A first comparison circuit that compares data output from the first F / V conversion circuit and data relating to an oscillation frequency at a reference temperature and pressure stored in the storage device and outputs the difference;
A second storage device in which output data of the first comparison circuit is temporarily stored;
A second switch linked to the first switch and disposed between the first comparison circuit and the second storage device;
A second comparison circuit that compares the data output from the second F / V conversion circuit with the data relating to the oscillation frequency at the reference temperature and pressure stored in the storage device and outputs the difference;
A second switch that is linked to the first switch and is arranged at a subsequent stage of the second comparison circuit;
An arithmetic circuit that calculates and outputs temperature and pressure data at a reference temperature based on data of the second storage device, the second comparison circuit, and the first storage device;
A surface acoustic wave device comprising: The surface acoustic wave device according to any one of claims 1 to 4,
A surface acoustic wave device, wherein the surface acoustic wave element and at least a circuit element forming the oscillation circuit are provided on the semiconductor substrate.

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