The present invention relates to an angular velocity detecting device including an oscillator having a piezoelectric film and a method of manufacturing the angular velocity detecting device.
There are known angular velocity detecting devices which have a micro electro-mechanical system (MEMS) structure and include a beam-type oscillator having a piezoelectric film and methods for manufacturing the angular velocity detecting devices. Patent Citation 1 discloses an angular velocity detecting device which includes an IC substrate and a gyro sensor element having a silicon substrate and an oscillator. A part of the oscillator is obtained by etching the silicon substrate. The oscillator includes a lower electrode, a piezoelectric film, and an upper electrode which are sequentially layered. The IC substrate includes an IC circuit which is connected to the upper and lower electrodes and controls the oscillator.
In this angular velocity detecting device, when angular velocity is applied to the oscillator vibrating in a predetermined direction by a drive signal from the IC substrate, the Coriolis force acts on the oscillator. Based on vibration due to the Coriolis force and vibration due to the drive signal, a vibration signal is outputted from the piezoelectric film of the oscillator through the upper electrode. The vibration signal is inputted into a control circuit and is then converted into an output signal based on the angular velocity to detect the angular velocity.
However, in the angular velocity detecting device described above, the oscillator and the IC substrate having the IC circuit controlling the oscillator are composed of different components. Accordingly, it is difficult to reduce the thickness of the angular velocity detecting device to 1 mm or less. The angular velocity detecting device is therefore difficult to miniaturize.
In the light of the aforementioned problem, an object of the present invention is to provide an angular velocity detecting device capable of being miniaturized and a method of manufacturing the angular velocity detecting device.
According to an aspect of the present invention, provided is an angular velocity detecting device, which includes: a semiconductor substrate; an oscillator formed on the semiconductor substrate; and a control circuit which is formed on the semiconductor substrate and controls the oscillator.
According to another aspect of the present invention, provided is a method of manufacturing an angular velocity detecting device including an oscillator having a plurality of beam-type electrodes, which includes: stacking a lower protective film, a lower electrode, a piezoelectric film, an upper electrode film, and a mask material on a semiconductor substrate; patterning the mask material; and etching the lower protective film, lower electrode, piezoelectric film, and upper electrode film of the oscillator at a same time.
According to the present invention, it is possible to provide an angular velocity detecting device which can be miniaturized and a method of manufacturing the angular velocity detecting device.
Next, first to third embodiments of the present invention are described with reference to the drawings. In the following description of the drawings, same or similar portions are given same or similar referential numerals or symbols. The drawings are schematic, and the relations between thicknesses and planar dimensions, the proportion of thicknesses of layers, and the like are different from the actual ones. Specific thicknesses and dimensions should be determined referring to the following description. Moreover, it is obvious that some portions have dimensional relations and proportions different in the drawings.
Moreover, the first to third embodiment shown below show examples of devices and methods embodying the technical idea of the present invention, and the technical idea of the present invention is not specified to the following materials, shapes, structures, arrangements, and the like of constituent components. Various modifications can be added to the technical idea of the present invention within the scope of the claims.
As shown in
As shown in
The semiconductor substrate 2 is a silicon (Si) substrate having a thickness of about 300 μm. The thickness of the semiconductor substrate 2 only needs to be large enough for the semiconductor substrate 2 to be held at mounting and the like and can be properly changed. In a planar view, the semiconductor 2 has a length of about 4.0 mm in the X direction and a length of about 4.5 mm in the Y direction. A part of the semiconductor substrate 2 under the oscillator 3 is etched to a depth of about 50 μm. This forms a cavity 7 with a height tg of about 50 μm between the semiconductor substrate 2 and the lower surface of the oscillator 3. The height tg of the cavity 7, which is not particularly limited, only needs to be large enough for the oscillator 3 not to be influenced by changes in air pressure caused between the oscillator 3 and semiconductor substrate 2 while the oscillator 3 is vibrating.
The oscillator 3 is formed as a beam capable of vibrating in the X-Z direction. The oscillator 3 is formed on the substrate 2. The oscillator 3 has a thickness t of about 2 to 6 μm in the Z direction and a width of about 5 to 6 μm in the X direction. The thickness t of the oscillator 3 is properly changed depending on a desired resonant frequency f in the Z direction. To increase the output sensitivity, it is preferable that the thickness t and the width of the oscillator 3 are equal to each other so that the cross-sectional shape thereof is square.
As shown in
The lower protective film 11 is configured to protect the lower surface of the lower electrode 12 and adjust the resonant frequency f. The lower protective film 11 is formed on the lower surface of the lower electrode 12. Between the lower surface of the lower protective film 11 and the semiconductor substrate 2, the cavity 7 with a predetermined height tg (for example, 50 μm) is formed. The height tg is not particularly limited and can be properly changed depending on the amplitude of the oscillator 3 in the Z direction. The lower protective film 11 is an SiO2 film having a thickness t1 of about 1 to 4 μm. By setting the thickness t1 of the lower protective film 11 based on Table 1 below, the resonant frequency f of the oscillator 3 is roughly adjusted. The concrete relationship between the lower protective film 11 and the resonant frequency f is shown in Table 1.
The lower electrode 12 is made of platinum (Pt) with a thickness of about 200 nm and is formed so as to cover the lower surface of the piezoelectric film 13. The lower electrode 12 is connected to a drive circuit 31 through one of the wires 6 within a via hole 8.
The piezoelectric film 13 changes in voltage based on angular velocity of rotational motion of the oscillator 3 around the Y axis. The piezoelectric film is a piezoelectric zirconate titanate (PZT) film having a thickness of about 1 μm and is formed so as to cover the upper surface of the lower electrode 12.
The upper electrode 14 is composed of an iridium oxide (IrO2)/iridium (Ir) layered film with a thickness of about 200 nm. The upper electrode 14 is formed on the upper surface of the piezoelectric film 13 so as to extend in the Y direction. The upper electrode 14 includes a drive electrode 21 and a pair of detection electrodes 22 and 23. The drive electrode 21 is connected to the drive circuit 31 through one of the wires 6. The drive electrode 21 receives from the control circuit 4, a drive signal SM to vibrate the oscillator 3 in the Z direction. The detection electrodes 22 and 23 are formed at positions opposite to each other across the drive electrode 21. The detection electrodes 22 and 23 are connected to the detection circuit 32 through some of the wires 6. The detection electrodes 22 and 23 respectively output to the control circuit 4, vibration signals SV1 and SV2 containing changes in voltage of the piezoelectric film due to the angular velocity generated when the oscillator 3 rotates around the Y axis.
The upper protective film 15 protects the lower electrode 12, piezoelectric film 13, and upper electrode 14. The upper protective film 15 is formed so as to cover the side surfaces of the lower electrode 12, the upper and side surfaces of the piezoelectric film 13, and the upper surface of the upper electrode 14. The upper protective film 15 is a SiO2 film having a thickness t2 of about 0.5 to 1.0 μm. By adjusting the thickness t2 of the upper protective film 15, the resonant frequency f is finely tuned.
The control circuit 4 controls the oscillator 3. The control circuit 4 is formed on the semiconductor substrate 2 monolithically with the oscillator 3. The control circuit 4 includes the drive circuit 31, the detection circuit 32, and a detector circuit 33.
The drive circuit 31 outputs the drive signal SM to the drive electrode 21 to vibrate the oscillator 3 at a predetermined resonant frequency f in the Z direction. The drive circuit 31 outputs a synchronizing signal SS to the detector circuit 33. The detection circuit 32 detects the detection signal SD based on the angular velocity of the oscillator 3 from the vibration signals SV1 and SV2 based on the vibration of the oscillator 3 outputted from the detection electrodes 22 and 23 of the oscillator 3, and the detection circuit 32 outputs the detection signal SD to the detector circuit 33. The detector circuit 33 detects the detection signal SD inputted from the detection circuit 32. Moreover, the detector circuit 33 synchronizes the detected signal with the synchronizing signal SS inputted from the drive circuit 31 and outputs an output signal SO based on the angular velocity acting on the oscillator 3. The drive circuit 31, detection circuit 32, and detector circuit are composed of transistors and the like monolithically formed on the semiconductor substrate 2.
Next, the operation of the aforementioned angular velocity detecting device 1 is described.
First, the drive signal SM of about 5 V is inputted from the drive circuit 31 to the drive electrode 21. The oscillator 3 therefore vibrates in the Z direction. By the vibration of the oscillator 3, the vibration signals SV1 and SV2 having polarities opposite to each other are outputted from the detection electrodes 22 and 23 to the detection circuit 32, respectively. Herein, when the oscillator 3 is rotated around the Y axis by an external force, the oscillator 3 including the piezoelectric film 13 vibrates also in the X direction. This causes the piezoelectric film 13 vibrating in the X direction to change in voltage due to the angular velocity of the rotational motion. Accordingly, the vibration signals SV1 and SV2 outputted from the detection electrodes 22 and contain the change in voltage due to the angular velocity.
The detection circuit 32 calculates a difference between the vibration signals SV1 and SV2 having polarities opposite to each other to output the drive signal SD which does not contain a signal based on the vibration of the oscillator 3 in the Z direction by the drive signal SM. In the detector circuit 33, the signal from the drive circuit 31 is synchronized with the angular velocity signal to detect the detection signal SD. The output signal SO due to the angular velocity acting on the oscillator 3 is thus outputted, and the angular velocity is thus detected.
Next, a method of manufacturing the aforementioned angular velocity detecting device 1 is described.
First, as shown in
Next, a Pt film 52 for the lower electrode 12 is formed by sputtering. Thereafter, a PZT film 53 for the piezoelectric film 13 is formed on the Pt film 52 by a sol-gel process. Furthermore, an IrO2 film 54 for the upper electrode 14 is formed on the PZT film 53 by sputtering.
Next, as shown in
Next, an insulating film composed of a SiO2 film is formed on the upper surface by a CVD process. As shown in
Next, as shown in
The angular velocity detecting device 1 is thus completed.
In the angular velocity detecting device 1 according to the first embodiment, as described above, the control circuit 4 is monolithically formed on the semiconductor substrate 2 where the oscillator 3 is formed. Accordingly, the thickness of the angular velocity detecting device 1 can be made small. Moreover, the longitudinal and transverse dimensions of the angular velocity detecting device 1 in a planer view can be made small, thus achieving miniaturization of the angular velocity detecting device 1. Specifically, it is possible to realize a thickness of not more than 1 mm that allows the angular velocity detecting device 1 to be mounted on mobile phones and the like.
Moreover, by integrally forming the oscillator 3 and control circuit 4 on the semiconductor substrate 2, it is possible to omit processes of bonding, adjustment, and the like of an oscillator and a control circuit which are necessary when the oscillator and control circuit are composed of different components.
If the oscillator constitutes a single component alone, a holder to hold the oscillator is necessary, thus increasing the size of the oscillator. However, by integrally forming the oscillator 3 and control circuit 4, it is possible to easily hold the oscillator 3 without forming a holder or the like, thus preventing damage of the oscillator 3.
Moreover, the insulating film 51 and semiconductor substrate 2 are patterned by dry etching to form the cavity 7 under the oscillator 3. This can prevent exposure of the side surfaces of the piezoelectric film 13. It is therefore possible to prevent the piezoelectric film 13 from being etched and further prevent the piezoelectric film 13 from being physically damaged in use.
Furthermore, by covering the upper and lower surfaces of the oscillator 3 with the lower and upper protective films 11 and 15, the resonant frequency f of the oscillator 3 can be easily set to a desired frequency using the thicknesses t1 and t2 of the lower and upper protective films 11 and 15.
The materials constituting the angular velocity detecting device 1 can be properly changed. Specifically, the protective films may be composed of insulating films (polysilicon, SiN, or the like) other than the SiO2 films. Moreover, the semiconductor substrate 2 may be a substrate composed of a semiconductor other than silicon.
Furthermore, in the above described example, the oscillator 3 is vibrated in the Z direction by the drive circuit 31. However, the oscillator 3 may be vibrated by the drive circuit 31 in the X direction.
Next, the second embodiment in which the present invention is applied to a biaxial angular velocity detecting device is described with reference to the drawings.
As shown in
The first oscillator 3A is formed on the semiconductor substrate 2 so as to extend in the X direction. The second oscillator 3B is formed on the semiconductor substrate 2 so as to extend in the Y direction. In other words, the first and second oscillators 3A and 3B are formed so as to extend in the directions orthogonal to each other. The first and second oscillators 3A and 3B then detect angular velocities in the directions orthogonal to each other. Specifically, the oscillator 3A detects the angular velocity around the X axis, and the oscillator 3B detects the angular velocity around the Y axis. Each of the oscillators 3A and 3B has the same configuration as that of the oscillator 3 of the first embodiment.
The first control circuit 4A controls the first oscillator 3A to detect angular velocity around the X axis. The second control circuit 4B controls the second oscillator 3B to detect angular velocity around the Y axis. The control circuits 4A and 4B are formed monolithically on the semiconductor substrate 2. Each of the control circuits 4A and 4B has the same configuration as that of the control circuit 4 of the first embodiment.
By including the two oscillators 3A and 3B, the angular velocity detecting device 1A shown in
Moreover, the two oscillators 3A and 3B are simultaneously formed. Accordingly, the biaxial angular velocity detecting device 1A can be easily manufactured. Furthermore, the two control circuits 4A and 4B can be simultaneously formed, and the biaxial angular velocity detecting device 1A can be therefore easily manufactured.
The above described example is the angular velocity detecting device including two oscillators. However, the present invention may be applied to an angular velocity detecting device including three or more oscillators.
As shown in the first and second embodiments, the piezoelectric material is provided on the semiconductor substrate 2 in a form of thin film. This can increase the processing accuracy of the piezoelectric material. However, as the oscillator 3 gets smaller and thinner, the symmetry of the shape of the oscillator 3 has a greater influence on the performance of the angular velocity detecting device 1. For example, if an oscillator has an asymmetric shape in a direction of vibration generated by the Coriolis force (in a detection direction), vibration in the detection direction will occur before the angular velocity is applied. This vibration is called “abnormal vibration”. In other words, the output of the oscillator becomes very small because of the miniaturization, and the abnormal vibration generated particularly in the detection direction because of the asymmetry of the oscillator prevents accurate detection of minute changes due to the Coriolis force.
As described below, in the angular velocity detecting device according to the third embodiment, the abnormal vibration due to the asymmetric shape of the oscillator can be reduced. As shown in
A method of manufacturing the oscillator 3 shown in
By dry etching the upper electrode film according to the power supply pattern, an electrode area 14A including the first to third beam-type electrodes 141 to 143 is formed. The electrode area 14A includes an area expanding from the outside of the second beam-type electrode 142 to the outside of the third beam-type electrode 143 across the first beam-type electrode 141. Herein, the sides of the second and third beam-type electrodes 142 and 143 facing the first beam-type electrode 141 are referred to as insides, and the sides thereof opposite to the insides are referred to as outsides. By continuously etching the lower protective film 11, lower electrode 12, piezoelectric film 13, and upper electrode film on the outside of the electrode area 14A by one dry etching, end faces of the lower protective film 11, lower electrode 12, piezoelectric film 13 are aligned with outside faces of the second and third beam-type electrodes 142 and 143.
Moreover, the intervals d12 and d13 are provided in the interval where the piezoelectric film 13 is not completely etched in the thickness direction by dry etching. Accordingly, between the first and second beam-type electrodes 141 and 142 and between the first and third beam-type electrodes 141 and 143, only the upper electrode film is completely etched, and the piezoelectric film 13 remains. The interval where the piezoelectric film 13 is not completely etched in the thickness direction by dry etching is described in detail later.
For the first to third beam-type electrodes 141 to 143 are formed by one dry etching, there is no misalignment of mask patterns caused when the electrode area 14A is formed using a plurality of etching masks. Accordingly, the oscillator 3 will not have asymmetric shape, and width W2 of the second beam-type electrode 142 and width W3 of the third beam-type electrode 143 can be made equal to each other as designed. Moreover, the intervals d12 and d13 can be made equal to each other.
The angular velocity detecting device shown in
For example, while the first beam-type electrode 141 as the drive electrode is vibrating in the vertical direction, the horizontal motion of the first beam-type electrode 141 generated by the Coriolis force is detected by the second and third beam-type electrodes 142 and 143 as the detection electrode. Alternatively, while the second and third beam-type oscillators are vibrating in the horizontal direction as the drive electrode, the vertical motions of the second and third beam-type electrodes 142 and 143 generated by the Coriolis force are detected by the first beam-type electrode 141 as the detection electrode. Specifically, the piezoelectric film 13 moves according to the voltage applied to the drive electrode, and the drive electrode vibrates in the drive direction. When the drive electrode is moved in the detection direction by the Coriolis force, the movement is converted into voltage by the piezoelectric film 13, and the detection electrode detects the converted voltage as the detection signal.
The drive circuit 31 is a circuit vibrating the first beam-type electrode 141 in the vertical direction. Specifically, the drive circuit 31 outputs to the first beam-type electrode 141 the drive signal to vibrate the first beam-type electrode 141 in the vertical direction.
The detection circuit 32 is a circuit detecting movement of the first beam-type electrode 141. Specifically, the detection circuit 32 receives a detected vibration signal generated as voltage by the second and third beam-type electrodes 142 and 143 according to the vibration of the first beam-type electrode 141.
The detector circuit 33 synchronously demodulates the detected vibration signal sent from the detection circuit 32 with the frequency of the drive vibration sent from the drive circuit 31 to output an angular velocity signal. The angular velocity signal is outputted through an output terminal OUT to the outside of the control circuit 4.
By integrally forming the oscillator 3 and control circuit 4 on the semiconductor substrate 2 into one chip, the angular velocity detecting device can be made smaller and thinner.
With reference to
Next, the mask material 16 is described. The mask material 16 is preferably a material having an etching selectivity higher than the photoresist film with respect to the piezoelectric film 13 made of a PZT film or the like. Specifically, the mask material 16 can be an indium tin oxide (ITO) film, an alumina (Al2O3) film, or the like. Since alumina generally has a low deposition rate, ITO is preferred.
Hereinafter, using
(1) First, on the semiconductor substrate 2 composed of a silicon substrate or the like, for example, the lower protective film 11, the lower electrode 12, the piezoelectric film 13, an upper electrode film 140, and the mask material 16 are stacked in this order to obtain a structural cross-section shown in
(2) Next, the photoresist film 17 is applied on the mask material 16, and as shown in
(3) Next, the mask material 16 is selectively removed by dry etching using the photoresist film 17 as a mask. For example, when the mask material 16 is made of an ITO film, the mask material 16 is etched using fluorine and Ar gases. The photoresist film 17 is then removed, thus obtaining the structural cross section shown in
(4) Using the mask material 16 as a mask, part of an upper electrode film 140, piezoelectric film 13, lower electrode 12, and lower protective film 11 on the outside of the second and third beam-type electrodes 142 and 143, that is, the outside of the electrode area 14A. Simultaneously, part of the upper electrode film 140 between the first and second beam-type electrodes 141 and 142 and part thereof between the first and third beam-type electrodes 141 and 143 are etched. As a result, as shown in
(5) The upper protective film 15 is formed on the entire surface of the oscillator 3 by sputtering or the like. The upper protective film 15 can be a SiO2 film or the like. At this time, as shown in
(6) The rear surface of the semiconductor substrate 2 is selectively etched by wet etching to form the cavity 7 under the oscillator 3 as shown in
(7) The upper protective film 15 is etched back to expose the upper surface of the mask material 16 and simultaneously expose the upper surface of the semiconductor substrate 2.
Another example of the method of selectively etching the rear surface of the semiconductor substrate 2 to form the cavity 7 is described below.
(1) After the structural cross-section shown in
(2) As shown in
The angular velocity detecting device manufactured by the aforementioned example of the manufacturing method has a structure in which the mask material 16 is provided on the first to third beam-type electrodes 141 to 143. The mask material 16 may be removed to obtain the structure shown in
As described above, in the method of manufacturing the angular velocity detecting device according to the third embodiment of the present invention, the intervals d12 and d13 are provided within the interval where the piezoelectric film 13 is not completely etched in the thickness direction by dry etching. The first to third beam-type electrodes 141 to 143 are thus formed by one dry etching.
On the other hand, for etching each of the films constituting the oscillator 3, mask patterns for etching of each layer are prepared, and the first to third beam-type electrodes 141 to 143 are formed with the mask patterns being aligned. For example, in the case of an angular velocity detecting device of a large device size with a thickness of the oscillator 3 of not less than 100 μm, slight asymmetry of about 0.1 μm in the shape of the oscillator will not cause a problem of the accuracy in detecting the angular velocity. However, in the case of an angular velocity detecting device having a thickness of the oscillator 3 of about 10 μm, the output of the oscillator 3 is very small, and such slight asymmetry of about 0.1 μm in the shape of the oscillator due to misalignment of mask patterns or the like will cause abnormal vibration, thus degrading the accuracy in detecting the angular velocity.
For example, it is assumed that in the oscillator 3 shown in
However, as described above using
As described above, the present invention is described with the first to third embodiments, but it should not be understood that the present invention is limited by the description and drawings constituting part of the disclosure. From this disclosure, various substitutive embodiments, examples, and operational techniques will be apparent to those skilled in the art.
In the above description of the first to third embodiments, the oscillator 3 is a cantilever-type oscillator. However, the oscillator 3 may be an oscillator of a fixed-fixed beam structure with the drive and detection electrodes supported at the center. Moreover, the number of electrodes is three but certainly not limited to three.
As described above, it is obvious that the present invention includes various embodiments and the like not described here. Accordingly, the technical scope of the present invention is determined only by the features of the invention according to the claims proper from the aforementioned description.
The angular velocity detecting device and the method of manufacturing the angular velocity detecting device of the present invention are applicable to electronics industries including manufacture manufacturing angular velocity detecting devices.
Number | Date | Country | Kind |
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2007-246787 | Sep 2007 | EP | regional |
2007-247885 | Sep 2007 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2008/067301 | 9/25/2008 | WO | 00 | 3/18/2010 |