JP2009231981A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device having a resonator with superior resonance characteristics without requiring a high electrostatic applied voltage. <P>SOLUTION: The semiconductor device 1 has a plurality of movable diaphragm portions 4, including at least a piezoelectric material layer and electrodes provided on the piezoelectric material layer and formed of a multilayer thin film, formed on a semiconductor substrate, the electrodes being a pair of electrode (first upper electrode 5 and second upper electrode 6) generating electric charges having the mutually opposite polarities. In two optional adjacent movable diaphragm portions 4 among the plurality of movable diaphragm portions 4, one upper electrode 5 of one movable diaphragm portion 4 and the other upper electrode 6 of the other movable diaphragm portion 4 are electrically connected, and the plurality of movable diaphragm portions 4 resonate such that electric charges having the same polarity are generated at both electrically connected upper electrodes 5 and 6 of two adjacent movable diaphragm portions 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor device, and more particularly to a semiconductor device provided with a resonator using a piezoelectric thin film.

  In recent semiconductor industries, integration of MEMS (Micro Electro-Mechanical System) and integrated circuits (Integrated Circuits) is progressing. In particular, technological development that integrates a resonator using a silicon material and an IC that controls the resonator is progressing, and this has accelerated the miniaturization and cost reduction of timing devices.

In recent years, a technique for first producing a silicon MEMS on a substrate as a timing device and then producing an integrated circuit using silicon CMOS has been disclosed (see Non-Patent Document 1). This technology forms a silicon resonator by deep etching silicon on an SOI (Silicon On Insulator) substrate, then deposits polycrystalline silicon, seals it by high-temperature processing, and then integrates CMOS. A circuit is formed. A method of making a silicon resonator as a separate chip and integrating it at the time of mounting is also disclosed (see Patent Document 1). Alternatively, a method of improving the Q value of resonance by mechanically connecting silicon resonators has been disclosed (see Non-Patent Document 2).
"Using MEMS To Build The Device And The Package", B. Kim, et al., TRANSDUCER & EUROSENSORS '07, pp331-334 "MEMS AND NANO TECHNOLOGY FOR THE HANDHELD, PORTABLE ELECTRONIC AND THE AUTOMOTIVE MARKETS", Albert P. Pisano, TRANSDUCER & EUROSENSORS '07, pp.1-3 US Pat. No. 6,930,569

  However, all of the techniques described in Non-Patent Document 1, Patent Document 1, and Non-Patent Document 2 apply a static electric field to a silicon structure to resonate, and a high electrostatic applied voltage. Is required. Therefore, a voltage source different from the power supply voltage (usually a voltage value higher than the power supply voltage) is required, and there is a problem that the electrical impedance becomes too high.

  The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a semiconductor device including a resonator having excellent resonance characteristics without requiring a high electrostatic applied voltage. .

  In order to achieve the above object, a semiconductor device according to the present invention includes a semiconductor substrate having a plurality of movable diaphragm portions made of a multilayer thin film including at least a piezoelectric layer and an upper electrode and a lower electrode sandwiching the piezoelectric layer. The upper electrode is formed on the upper electrode and has a combination of a pair of electrodes that generate charges having different polarities, and one movable movable diaphragm portion of any of the plurality of movable diaphragm portions is movable. One upper electrode of the pair of upper electrodes of the diaphragm portion and the other upper electrode of the pair of upper electrodes of the other movable diaphragm portion are electrically connected, and the two adjacent movable electrodes In the diaphragm portion, the plurality of movable diaphragm portions resonate so that charges having the same polarity are generated in both of the electrically connected upper electrodes. And wherein the door.

  That is, in the semiconductor device of the present invention, a plurality of movable diaphragm portions made of a multilayer thin film are formed on a semiconductor substrate, and a resonator is constituted by the plurality of movable diaphragm portions. When attention is paid to any two adjacent movable diaphragm portions among the plurality of movable diaphragm portions, one upper electrode of one movable diaphragm portion and the other upper electrode of the other movable diaphragm portion are electrically The plurality of movable diaphragm portions resonate so that charges of the same polarity are generated in both electrodes that are connected and electrically connected. Therefore, the vibration phases of adjacent movable diaphragm portions are reversed, and a plurality of movable diaphragm portions (that is, vibrators) having different phases are connected. As a result, since the vibrators are electrically connected, the resonance characteristics (Q value) can be improved. Also, in contrast to the conventional structure using a silicon structure as a vibrator, in the case of the present invention, a movable diaphragm portion including at least a piezoelectric layer and an electrode is used as a vibrator, so that an electrostatic applied voltage other than the power supply voltage is not required. Thus, the electrical impedance can be lowered.

In the present invention, the pair of upper electrodes are formed at a central portion and a peripheral portion of the movable diaphragm, and in the two adjacent movable diaphragm portions, the upper electrode at the central portion of one movable diaphragm portion and the other movable diaphragm. It is possible to adopt a configuration in which the upper electrode at the peripheral edge of the part is electrically connected.
According to this configuration, when tensile stress is applied to the central portion of one movable diaphragm portion, tensile stress is also applied to the peripheral portion of the other movable diaphragm portion, and compressive stress is applied to the central portion of one movable diaphragm portion. Sometimes two adjacent movable diaphragm portions vibrate so that compressive stress is also applied to the peripheral edge portion of the other movable diaphragm portion. Therefore, it is possible to specifically realize a configuration in which these two movable diaphragm portions reliably vibrate in opposite phases.

In the present invention, the lower electrode of the piezoelectric layer is formed at an intermediate position with respect to the film thickness of the movable diaphragm portion made of the multilayer thin film, and is connected to the same potential across the plurality of movable diaphragm portions. desirable.
Generally, when compressive stress is applied to the diaphragm surface, tensile stress is generated on the back surface of the diaphragm. Therefore, if the lower electrode of the piezoelectric layer is disposed on the rear surface of the diaphragm, the generated charges cancel each other out. In that respect, according to the configuration described above, since the stress generated in the piezoelectric layer can be limited to either compression or tension, efficient charge extraction can be performed.

In the present invention, it is desirable that the potential of the lower electrode of the piezoelectric layer is fixed to a potential that is half the power supply voltage.
According to this configuration, the pair of upper electrodes oscillate around the half of the power supply voltage, so that it is easy to oscillate by the oscillation circuit using the inverter circuit.

In the present invention, it is desirable that an odd number of the movable diaphragm portions be formed.
The number of movable diaphragms may be even, but if it is odd, the potential of the electrodes at the movable diaphragms at both ends will be reversed, so the configuration of the oscillator oscillation circuit that normally consists of an odd number of inverter circuits is simple. Can be. That is, when the number of movable diaphragm portions is an odd number, the resonator oscillation circuit can be configured by the minimum number of one inverter circuit.

In the present invention, an integrated circuit may be formed on the semiconductor substrate.
According to this configuration, a semiconductor device in which the resonator and the integrated circuit that controls the resonator are integrated can be realized.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
This embodiment is an example of a semiconductor device in which a resonator having a plurality of movable diaphragm portions and an integrated circuit are integrated.
FIG. 1 is a plan view of the semiconductor device of this embodiment. FIG. 2 is a cross-sectional view taken along the line AA ′ of FIG. FIG. 3 is a diagram for explaining the operation of the resonator in the semiconductor device of this embodiment. FIG. 4 is a block diagram showing an oscillation circuit of the resonator.

  As shown in FIG. 1, the semiconductor device 1 of this embodiment includes a resonator 2 and an integrated circuit 3. The resonator 2 is configured by electrically connecting three movable diaphragm parts 4 each serving as a vibrator. Each movable diaphragm portion 4 is substantially circular in plan view, and a circular first upper electrode 5 is formed at the center of a circle that defines the outline of the movable diaphragm portion 4, and a substantially annular second upper portion is formed at the periphery of the circle. An electrode 6 is formed. The integrated circuit 3 includes, for example, a resonator driving circuit, a resonance frequency detection circuit, a signal generation circuit that generates a signal having an arbitrary frequency from the detected resonance frequency, and the like. The integrated circuit 3 is composed of a CMOS circuit.

  When attention is paid to any two adjacent movable diaphragm parts 4 among the three movable diaphragm parts 4, the first upper electrode 5 of the right movable diaphragm part 4 and the first movable diaphragm part 4 of the left side in FIG. 2 The upper electrode 6 is electrically connected by a linear connection portion 7. At the position through which the connecting portion 7 passes, the ring that forms the outline of the second upper electrode 6 is cut off, and the second upper electrode 6 and the connecting portion 7 are not in contact with each other. Further, the second upper electrode 6 of the rightmost movable diaphragm portion 4 is electrically connected to the terminal 8 via the connection portion 7, and the first upper electrode 5 of the leftmost movable diaphragm portion 4 is connected to the terminal via the connection portion 7. 8 is electrically connected. In the above description, the expression “the first upper electrode 5, the second upper electrode 6, the connection portion 7, etc. are electrically connected” is used. Is formed.

In the semiconductor device 1 of the present embodiment, as shown in FIG. 2, an SOI (Silicon On Insulator) substrate 13 in which a silicon single crystal layer 12 is laminated on an insulating substrate 10 with an insulating film 11 interposed therebetween is used. . The SOI substrate 13 is formed with a space 14 partially removed from the back surface side, and a pair of electrodes of a lower electrode 15 and an upper electrode 16 (first upper electrode 5 and second upper electrode 6) above the space 14. The movable diaphragm portion 4 is formed of a multilayer thin film composed of the piezoelectric layer 17 sandwiched between the upper and lower electrodes and the oxide film layer 21 locally oxidized by the local oxidation method. The piezoelectric layer 17 may be an insulating thin film exhibiting piezoelectricity, and zinc oxide (ZnO), aluminum nitride (AlN), lithium niobate (LiNbO ₃ ), or the like can be used. In this embodiment, aluminum nitride that is easily obtained by reactive sputtering is used. The lower electrode 15 is made of, for example, a platinum (Pt) thin film. However, the lower electrode 15 may be another metal thin film as will be described later. An arbitrary metal film can be used for the upper electrode 16.

  When manufacturing the semiconductor device 1 having the above configuration, first, a CMOS circuit forming the integrated circuit 3 is formed on the SOI substrate 13. At this time, a silicon oxide film 19 is formed on the surface of the SOI substrate 13, and a part of the silicon oxide film 19 is grown thickly by a local oxidation method or the like. In this embodiment, an oxide film layer 21 having a thickness of about 1 μm is formed on a SOI wafer having a top silicon layer 20 μm by a local oxidation method. Thereafter, a wiring layer for connecting the integrated circuit 3 and the resonator 2 is formed. Next, a platinum thin film to be the lower electrode 15 is formed to a thickness of about 100 nm in a region to be the vibrator, and the platinum thin film is patterned by photolithography and etching methods to form the lower electrode 15. However, a titanium thin film 50 nm may be inserted in order to improve the adhesion between the platinum thin film and the oxide film layer 21. Next, an aluminum nitride film to be the piezoelectric layer 17 is formed by a reactive sputtering method or the like.

  It is widely known that when an aluminum nitride film is formed on a platinum thin film, the aluminum nitride film grows while being oriented in the C-axis direction of the wurtzite structure. As a result, the aluminum nitride film becomes a columnar crystal film, and piezoelectric characteristics are obtained. When an aluminum nitride film is deposited, for example, about 1 μm, columnar crystal grains having a radius of about 80-200 μm grow. The metal film that promotes C-axis orientation is not limited to platinum, but FCC structure metal films such as gold (Au), aluminum (Al), and nickel (Ni), molybdenum (Mo), cobalt (Co), A Hexa structure metal film such as titanium (Ti) can be used. The piezoelectric layer 17 is not limited to aluminum nitride, and other wurtzite structure crystal films such as zinc oxide (ZnO) can be used.

  After the piezoelectric layer 17 is formed, an arbitrary metal film is formed and patterned to form the upper electrode layer 16 (the first upper electrode 5 and the second upper electrode 6). By this step, the first upper electrode 5 and the second upper electrode 6 having a pattern as shown in FIG. 1 are formed. Finally, deep etching is performed from the back surface of the SOI substrate 13 toward the oxide film layer 21 on which the silicon oxide film has grown to remove the insulating substrate 10, the insulating film 11, and the silicon single crystal layer 12, and the oxide film layer A space 14 is formed below 21. Through this step, the laminated body of the oxide film layer 21, the lower electrode 15, the piezoelectric layer 17, and the upper electrode 16 can bend and vibrate in the vertical direction in FIG.

  When a driving voltage is applied to the resonator 2 having the above-described configuration, for example, as shown in FIG. 3, among the three movable diaphragm portions 4, the right and left movable diaphragm portions 4 are upward, and the central movable diaphragm portion 4 is downward. If bent, tensile stress is generated in the central part of the right and left movable diaphragm parts 4, compressive stress is generated in the peripheral part, compressive stress is generated in the central part of the central movable diaphragm part 4, and tensile stress is generated in the peripheral part. become. At this time, assuming that a positive charge is generated by tensile stress and a negative charge is generated by compressive stress, the first upper electrode 5 of the right and left movable diaphragm parts 4 is positive, the second upper electrode 6 is negative, the center Thus, negative charges are generated in the first upper electrode 5 and positive charges are generated in the second upper electrode 6 of the movable diaphragm portion 4. In this case, positive charges can be extracted from the left terminal 8 of the resonator 2 and negative charges can be extracted from the right terminal 8. At the next moment, on the contrary to FIG. 3, the right and left movable diaphragm parts 4 bend downward and the central movable diaphragm part 4 bends upward. In this way, the adjacent movable diaphragm portions 4 resonate while oscillating so as to be in opposite phases.

  At this time, the lower electrode 15 of the piezoelectric layer 17 is disposed at an intermediate position with respect to the film thickness of the entire movable diaphragm portion 4 made of a multilayer thin film. Specifically, in the movable diaphragm portion 4 of the multilayer thin film, the lower electrode 15 made of platinum is sandwiched between the oxide film layer 21 having a thickness of 1 μm and the aluminum nitride piezoelectric layer 17 having a thickness of 1 μm. . According to such a configuration, only one of the compressive stress and the tensile stress is generated in the piezoelectric layer 17, and charges can be generated efficiently.

  Further, when the lower electrode 15 is electrically connected across the plurality of movable diaphragm portions 4 and fixed to a potential of ½ of the power supply voltage, the first upper electrode 5 and the second upper electrode 6 are ½ of the power supply voltage. Therefore, it is easy to obtain an oscillation phenomenon by the inverter circuit. In this embodiment, the potential of all the lower electrodes 15 is fixed at 1.65 V with respect to the power supply voltage 3.3 V.

  As shown in FIG. 4, the oscillation circuit 19 from the resonator 2 has an input / output of an inverter 20 connected between terminals 8 at both ends of the resonator 2, and a power supply voltage (Vdd) and a ground voltage are applied to the inverter 20. Further, the lower electrode 15 of the resonator 2 was fixed to a potential (1/2 · Vdd) that is half of the power supply voltage.

  As described above, the semiconductor device 1 according to the present embodiment includes the resonator 2 to which a plurality of anti-phase movable diaphragm portions 4 (vibrators) are connected, so that the resonance characteristics (Q value) are improved. be able to. Further, compared to the conventional structure using a silicon structure as a vibrator, the thin movable diaphragm portion 4 serves as a vibrator, so that an electrostatic applied voltage is not required. Further, in the case of the present embodiment, since there are an odd number of movable diaphragm portions 4, the configuration of the oscillator oscillation circuit can be configured with the minimum number of inverter circuits.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, an example of a resonator having three (odd number) movable diaphragm portions has been described. However, an even number of movable diaphragm portions may be used. In that case, the oscillation circuit shown in FIG. 4 may be one in which two inverters are connected in series. In addition, the constituent material, the shape, the electrode shape, the formation position, and the like of the movable diaphragm portion are not limited to the above-described embodiment, and can be changed as appropriate.

It is a top view of the semiconductor device of one embodiment of the present invention. It is sectional drawing which follows the A-A 'line of FIG. It is a figure for demonstrating operation | movement of the resonator of the semiconductor device of this embodiment. It is a block diagram which shows the oscillation circuit of a resonator.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor device, 2 ... Resonator, 3 ... Integrated circuit, 4 ... Movable diaphragm part, 5 ... 1st upper electrode, 6 ... 2nd upper electrode, 15 ... Lower electrode, 16 ... Upper electrode layer, 17 ... Piezoelectric body layer .

Claims (6)

A plurality of movable diaphragm portions made of a multilayer thin film including at least a piezoelectric layer and an upper electrode and a lower electrode sandwiching the piezoelectric layer are formed on a semiconductor substrate,
The upper electrode has a combination of a pair of electrodes that generate charges of different polarities,
In any two adjacent movable diaphragm portions of the plurality of movable diaphragm portions, one upper electrode of the pair of upper electrodes of one movable diaphragm portion and the pair of upper portions of the other movable diaphragm portion The other upper electrode of the electrodes is electrically connected,
2. The semiconductor device according to claim 1, wherein in the two adjacent movable diaphragm portions, the plurality of movable diaphragm portions resonate so that charges of the same polarity are generated in both of the electrically connected upper electrodes. The pair of upper electrodes are formed at a central portion and a peripheral portion of the movable diaphragm,
2. The adjacent two movable diaphragm portions, wherein the upper electrode at the center of one movable diaphragm portion and the upper electrode at the peripheral portion of the other movable diaphragm portion are electrically connected. A semiconductor device according to 1.   The lower electrode of the piezoelectric layer is formed at an intermediate position with respect to the film thickness of the movable diaphragm portion made of the multilayer thin film, and is connected to the same potential over the plurality of movable diaphragm portions. Item 3. The semiconductor device according to Item 1 or 2.   4. The semiconductor device according to claim 1, wherein the potential of the lower electrode of the piezoelectric layer is fixed to a half of the power supply voltage. 5.   The semiconductor device according to claim 1, wherein an odd number of the movable diaphragm portions are formed.   6. The semiconductor device according to claim 1, wherein an integrated circuit is formed on the semiconductor substrate.

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