JP5016207B2 - Piezoelectric thin film transformer and manufacturing method thereof - Google Patents

Description

  The present invention relates to a piezoelectric thin film transformer used for various high voltage generating power supply devices, and more particularly to a piezoelectric thin film transformer that can be reduced in size and thickness.

  Conventionally, wound-type electromagnetic transformers have been used as transformer elements used in various home appliances, AV equipment and other electronic equipment. This electromagnetic transformer has a structure in which a conducting wire is wound around a magnetic core. In order to realize a high transformation ratio, it is necessary to increase the number of conducting wires to be wound. For this reason, it has been very difficult to realize a small and thin electromagnetic transformer.

  For such an electromagnetic winding transformer, a piezoelectric transformer has been proposed (see Patent Document 1). This piezoelectric transformer has a completely different operating principle from a conventional electromagnetic transformer. FIG. 5 is a perspective view showing a configuration of a single plate type piezoelectric transformer, a so-called Rosen type piezoelectric transformer. Hereinafter, the configuration of the piezoelectric transformer will be described with reference to FIG.

  The portion where the planar electrodes 14 and 10 are provided on the upper and lower surfaces of the piezoelectric body A is the drive unit 11, and the piezoelectric body A is polarized in the thickness direction. A portion sandwiched between the end face electrode 26 provided at the end of the piezoelectric body A and the drive unit 11 is the power generation unit 12, and the piezoelectric body A is polarized in the length direction. The piezoelectric transformer having such a structure is provided with a support 27 provided at a position where one of the apexes of the triangular prism contacts the lower surface of the piezoelectric transformer, for example, at a node at the time of resonance of longitudinal vibration in the longitudinal direction, Fix to a transformer base (not shown). In this state, when an AC voltage having a resonance frequency of longitudinal vibration in the longitudinal direction of the piezoelectric body is applied via the external input electrical terminals 6 and 21 connected to the upper planar electrode 14 and the lower planar electrode 10, the external input A voltage is generated between the electrical terminal 6 and the external output electrical terminal 23 connected to the end face output electrode 26.

  However, as shown in FIG. 5, since the connection position of the external input / output electrical terminal is different from the vibration node in both the drive unit and the power generation unit, there is a problem that efficiency and reliability are lowered. Further, since the piezoelectric transformer shown in FIG. 5 has a single plate structure, there is a problem that the step-up ratio cannot be sufficiently increased.

  In order to solve these problems, a multilayer piezoelectric transformer using a multilayer ceramic has been proposed. According to Patent Document 2, the multilayer piezoelectric transformer is composed of a low-impedance driving unit and a high-impedance power generation unit. The low-impedance drive unit has a plurality of alternately laminated planar internal electrodes and piezoelectric bodies (polarized in the thickness direction), and planar electrodes are provided on the upper and lower surfaces. It is formed on the side. In addition, the high-impedance power generation unit is configured by alternately laminating strip-shaped internal electrodes and piezoelectric bodies (polarized in the length direction), providing strip-shaped electrodes on the upper and lower surfaces, and connecting external electrodes to connect the internal electrodes. It is formed on the side. Since the piezoelectric transformer with such a structure can connect external input / output electrical terminals at the nodes of longitudinal vibration in the longitudinal direction, the efficiency and reliability are not lowered as described for the Rosen piezoelectric transformer, and the boost ratio is Can also be taken big.

These piezoelectric transformers described in the Rosen type (Patent Document 1) and the laminated type (Patent Document 2) use ceramics, although the device structure is different from the single plate structure and the laminated structure. Such a ceramic is usually fired by a high-temperature process of 1000 ° C. or higher and separately disposed on a transformer substrate.
US Pat. No. 2,830,274 Japanese Patent No. 2508575

However, the two piezoelectric transformers have the following problems.
The piezoelectric transformers disclosed in the conventional Rosen-type piezoelectric transformer (Patent Document 1) and multilayer piezoelectric transformer (Patent Document 2) have a structure in which a transformer body is retrofitted to a transformer base, and can be reduced in size and thickness. There was a problem that it was difficult.

  Further, the configuration in which the piezoelectric transformer is retrofitted complicates the device structure, which increases the number of parts of the piezoelectric transformer, complicates the process, and increases the manufacturing cost. If the piezoelectric transformer is previously provided on the base of the transformer, the ceramic forming process is performed at a high temperature of 1000 ° C. or higher, which causes thermal damage to the transformer base.

  In addition, when trying to integrate a piezoelectric transformer and peripheral circuits, wiring to ceramics is possible, but there is a limit to micron-level miniaturization, and functional integration (functional integration) is difficult. It was.

  The present invention has been made to solve the above-described problems, and is a piezoelectric device that enables at least one of downsizing, thinning, functional integration of peripheral circuits and the like, cost reduction, and further low temperature processing. An object is to provide a thin film transformer.

  In order to achieve the above object, the piezoelectric thin film transformer of the present invention deposits a piezoelectric material, an electrode material, a wiring material, an insulating material, etc. on a semiconductor substrate, and processes each into a desired shape to form a groove. By doing so, the functional structure of the transformer is constructed.

  In the piezoelectric thin film transformer of the present invention, a piezoelectric body is bridged in a groove portion of a semiconductor substrate, and the piezoelectric body is supported by using a via of the lower electrode wiring structure on the input side at the node of mechanical resonance. Is physically suspended by the output side electrode wiring. In addition, a driving circuit, a control circuit, and the like are formed in advance on a semiconductor substrate that is a thin film using a deposited film (different from ceramics that are generally used).

  A method of manufacturing such a piezoelectric thin film transformer includes a step of forming an input-side lower electrode structure on a semiconductor substrate, a step of forming a piezoelectric body on the input-side electrode, and an input-side upper electrode wiring structure on the piezoelectric body. A step of forming the output side left and right electrode wiring structures and a step of hollowing the piezoelectric body. Preferably, the step of forming the piezoelectric body on the input side electrode includes orientation control. More preferably, an MOCVD (Metal Organic Chemical Deposition) method or an MBE (Molecular Beam Epitaxy) method is used for the step of forming a piezoelectric body on the input side electrode.

  According to the present invention, a piezoelectric thin film transformer that can be reduced in size and thickness can be manufactured. Compared with conventional piezoelectric transformers using ceramics, the piezoelectric thin film transformer not only reduces the device structure and reduces the number of parts, but also can be manufactured using simple processes, greatly reducing costs. be able to. In addition to being able to proceed with the process at a low temperature, it is possible to manufacture the integrated circuit with a peripheral circuit or the like. Moreover, it becomes easy by using the base | substrate from which the orientation control of the thin film to deposit differs.

  The piezoelectric thin film transformer according to the first embodiment of the present invention will be described below. FIG. 1 is a perspective view showing the appearance and configuration of a piezoelectric thin film transformer according to the present embodiment. The piezoelectric thin film transformer according to the present embodiment is greatly different in device configuration and manufacturing method from the conventional piezoelectric transformer using ceramics in that a deposited film is used as a piezoelectric body.

  The driving unit 11 and the power generation unit 12 of the piezoelectric thin film transformer are formed by controlling the orientation by a MOCVD (Metal Organic Chemical Deposition) method, an MBE (Molecular Beam Epitaxy) method, or the like.

  By precisely controlling the orientation in this way, almost 100% orientation control can be realized with respect to the polarization direction, so that deterioration of the piezoelectric characteristics can be suppressed even if the film thickness is reduced. On the other hand, in the case of conventional ceramics, it is difficult to reduce the thickness because only about 30% orientation can be realized. As described above, when a thin film is used for the piezoelectric transformer, it is possible to reduce the film thickness to about 1/3 compared to ceramic, which is suitable for making the piezoelectric transformer small and thin.

The orientation control technique of the piezoelectric thin film can be achieved by, for example, modifying the lower electrode that is the base of the piezoelectric thin film. That is, the substrate dependency of the orientation of the piezoelectric thin film is used. For example, lead titanate (PbTiO ₃ : PTO), which is a known piezoelectric material, is C-axis oriented on magnesium oxide MgO (100) or platinum Pt (100) / Mg (100), and Pt (111) / On Mg (100), the A-axis orientation is obtained. Therefore, by providing different base materials for the drive unit and the power generation unit of the piezoelectric thin film transformer, two types of piezoelectric thin films having different orientations can be selectively formed even when the piezoelectric films are deposited simultaneously. it can.

  Such a piezoelectric thin film has the planar electrodes 10 and 14 on the upper and lower surfaces of the drive unit 11, and the piezoelectric thin film having the planar electrodes 10 and 14 on the upper and lower surfaces is composed of the input side upper wiring 21 and the input side lower wiring 6. Are supported by being sandwiched between vias 9a and 9b that are electrically connected to each other. The vias 9a and 9b are provided at the node of mechanical resonance, and as a result, the efficiency reduction is suppressed to the maximum. Further, the piezoelectric thin film is provided with end face electrodes 15 and 16 at both ends in the longitudinal direction, and the output side left wiring 22 and the output are electrically connected to these end face electrodes 15 and 16 via vias 9c and 9d. The side right wiring 23 is physically suspended in the groove G provided on the semiconductor substrate 1. Such a hanging structure may use either one or both of the output wirings. Further, in order to electrically insulate the output side wirings 22 and 23 and the input side lower wiring 6, interlayer insulating films 7 and 17 are provided. In the figure, the groove G is formed by forming openings in the interlayer insulating films 7 and 17.

  As the piezoelectric thin film, a lead zirconate titanate piezoelectric material (k31 = 35%, k33 = 65%, Qm = around 2000) is used. The dimensions are 32 mm in length, 4.5 mm in width, and 0.5 mm in film thickness. did. When the drive unit 11 is polarized in the film thickness direction and the power generation unit 12 is polarized in the longitudinal direction, the step-up ratio (output voltage / input voltage) is about 8 and the efficiency is about 85 to 90% with an input power of 0.2 W. The piezoelectric transformer characteristics were obtained.

  Next, an example of a method for manufacturing the piezoelectric thin film transformer according to the present embodiment will be described with reference to FIGS.

  FIG. 2A is a structural cross-sectional view for explaining a manufacturing process of the piezoelectric thin film transformer after forming a drive circuit, a control circuit, and the like on the semiconductor substrate 1. The semiconductor substrate 1 uses a silicon (Si) substrate. On the semiconductor substrate 1, an element isolation region 2 by a known LOCOS method, a gate electrode 3, a diffusion layer (source / drain) 4, and an interlayer insulation are used. A film 5 is formed. When flatness of the interlayer insulating film 5 is required, the interlayer insulating film 5 can be polished and flattened appropriately using a CMP (Chemical Mechanical Polishing) process.

  Furthermore, it is preferable to previously form contacts and wirings for electrical connection to the piezoelectric transformer portion formed in the upper layer of such an integrated circuit. Instead of forming a drive circuit and a control circuit on such a silicon substrate, it is also possible to use the silicon substrate as a simple transformer support base and to form a drive circuit and a control circuit on another substrate.

  FIG. 2B is a diagram illustrating a process following FIG. 2A, and is a cross-sectional view of the piezoelectric thin film transformer after the input side lower electrode wiring structure is formed. As shown in FIG. 2B, an input-side lower wiring material is deposited on the interlayer insulating film 5 and processed into a desired pattern by photolithography and etching to form a first input-side lower wiring 6. Next, an interlayer insulating film 7 is deposited, and subsequently an orientation control layer 8 is deposited. As shown in FIG. 2C, after the pattern for the second input side lower electrode is formed on the first input side lower wiring 6, the input side lower via pattern is processed to obtain a dual damascene (wiring and via). The second input-side lower electrode 10 and the input-side lower via 9 are formed by the step of forming a conductive layer simultaneously.

  FIG. 3A is a cross-sectional view of the piezoelectric thin film transformer after electrode wiring material is deposited on the piezoelectric thin film. The piezoelectric thin film can be deposited by various methods depending on the required film quality and film thickness. When there is a demand for higher quality for the piezoelectric thin film to be deposited, it is preferable to deposit the piezoelectric thin film at about several hundred degrees Celsius using the MOCVD method or the MBE method with high density and good orientation. In this case, since the deposition rate is slow, the productivity is deteriorated when it is necessary to deposit several tens of μm, but the orientation rate in the film thickness direction of the piezoelectric thin film can be made almost 100%. When there is a strong demand for thickening the piezoelectric thin film to be deposited, the orientation of the piezoelectric thin film is not so favorable by using the AD (Aerosol Deposition) method, and the film quality of the thin film deposited by the MOCVD method or MBE method. Is difficult to reproduce, but a piezoelectric thin film having a film thickness of about several tens of μm can be deposited at room temperature.

  As an intermediate deposition method, a sol-gel method can be used. The piezoelectric thin film deposited by the sol-gel method has an advantage that the orientation rate is relatively high and deposition of a film thickness of about several tens of μm can be relatively easily performed at a low temperature of about several hundred degrees Celsius. Whichever deposition method is used, the characteristics of the base, for example, in this embodiment, the second input side lower electrode 10 (for example, Pt (111)) and the orientation control layer 8 (for example, MgO) are used. However, by changing the material type in this way, piezoelectric thin films having different orientation directions can be formed. Further, it is necessary to form an insulating region by doping a large amount of a substance such as silicon at the boundary between the drive layer 11 and the power generation layer 12 and performing annealing in an oxygen atmosphere at about 600 ° C. . In this way, after patterning the piezoelectric thin film having the drive unit 11 and the power generation unit 12 having different orientation directions, the electrode wiring material 13 is deposited thereon.

  FIG. 3B is a structural cross-sectional view of the piezoelectric thin film transformer showing a state in which the interlayer insulating film 17 is deposited thereon after the input-side upper planar electrode 14 and the output-side end face electrodes 15 and 16 are formed. It is preferable to process by a photolithography technique and an etching technique using a mask of an input side upper plane electrode pattern, an output side left end face electrode pattern, and an output side right end face electrode pattern. In this way, the input-side upper flat electrode 14, the output-side left end face electrode 15, and the output-side right end face electrode 16 can be formed with high accuracy. In this case, it is an important design point to provide a space for ensuring electrical insulation between the input-side upper flat electrode 14 and the output-side left end face electrode 15. Subsequently, an interlayer insulating film 17 is deposited on the input-side upper flat electrode 14, the output-side left end face electrode 15, and the output-side right end face electrode 16.

  FIG. 4A is a cross-sectional view of a piezoelectric thin film transformer showing a state in which a suspended structure (bridge structure) is formed on the piezoelectric thin film. First, as in the case of FIG. 2C, the input-side upper via 18 and the input-side upper wiring 21 and the output-side left end face electrode 15 are formed with respect to the input-side upper planar electrode 14 using the dual damascene method. An output-side right via 20 and an output-side right wiring 23 are formed on the output-side left via 19, the output-side left wiring 22, and the output-side right end face electrode 16. In order to make the piezoelectric thin film into a suspended structure (bridge structure), the interlayer insulating films 7 and 17 in a desired region are removed by etching to form a gap (etching region) 24 with respect to the interlayer insulating films 7 and 17. At this time, it is important to use an etchant having a high etching selectivity between the interlayer insulating films 7 and 17 and the piezoelectric thin film. If it is difficult to ensure the etching selectivity, it is preferable to reduce the process damage to the piezoelectric thin film as much as possible by covering the piezoelectric thin film with an etching protective layer.

  FIG. 4B is a process cross-sectional view after the piezoelectric thin film transformer manufacturing process is completed. As is apparent from the figure, the orientation control layer 8 is removed by etching, whereby the piezoelectric thin film can be suspended like a bridge. In the present embodiment, only the output side right end face electrode wiring structure is suspended, but the output side left end face electrode wiring structure is also suspended by using the same process. It is also possible.

  Through the steps described above, a piezoelectric thin film transformer that can be reduced in size and thickness can be manufactured. The piezoelectric thin film transformer according to the present embodiment has a simplified device structure and a reduced number of parts as compared to a conventional piezoelectric transformer using ceramics, and can be manufactured using a simple process. Can be greatly reduced. In addition, since no ceramic is used, an ultrahigh temperature process of 1000 ° C. or higher is not required, and integrated manufacturing with peripheral circuits and the like is possible. Furthermore, even when peripheral circuits are integrated, a semiconductor manufacturing process can be used, and thus a highly integrated device can be provided.

  In the above embodiment, an example in which a piezoelectric thin film transformer is formed on a semiconductor substrate has been described. However, an insulator substrate or the like may be used as the substrate. For example, a structure in which an insulator is deposited on a semiconductor substrate is also referred to as a substrate.

  The present invention can be used as a piezoelectric transformer.

1 is a perspective view of a piezoelectric thin film transformer according to an embodiment of the present invention. It is sectional drawing of the piezoelectric thin film transformer by this Embodiment. It is sectional drawing of the piezoelectric thin film transformer by this Embodiment. It is sectional drawing of the piezoelectric thin film transformer by this Embodiment. It is a perspective view of the conventional piezoelectric transformer.

Explanation of symbols

G groove
1 Silicon substrate
2 Locos (element isolation region)
3 Gate electrode
4 Diffusion layer
5 Interlayer insulation film
6 Input side lower wiring
7 Interlayer insulation film
8 Orientation control layer
9 Input side lower via
10 Lower planar electrode
11 Drive unit side piezoelectric thin film
12 Power generation unit side piezoelectric thin film
13 Wiring material layer
14 Upper planar electrode
15 Left end electrode
16 Right end electrode
17 Interlayer insulation film
18 Input side upper via
19 Output side left via
20 Output side right via
21 Input side upper wiring
22 Output side left wiring
23 Output side right wiring
24 Air gap to the interlayer insulation film
25 Air gap to the protective layer (non-etched area)
26 End face output electrode
27 Support

Claims (6)

A piezoelectric transformer having a drive unit and a power generation unit,
A substrate,
An input-side lower electrode structure formed on the substrate;
A piezoelectric body having a cantilever-like bridge structure in which the drive unit is formed on the input-side lower electrode and a base material formed between the power generation unit and the substrate is removed;
An input side upper electrode wiring structure formed on the piezoelectric body, an output side left and right electrode wiring structure, and
Have
Before thin film to be the Ki圧 collector, the are oriented controlled to have a different orientation in the power generation unit and the piezoelectric transformer drive portion in forming,
The orientation control is performed by providing the base material having a different orientation of the thin film from that of the lower electrode on the input side in a region where the power generation unit is formed , and utilizing the base dependency of the orientation of the thin film. A featured piezoelectric thin film transformer. The piezoelectric body is formed by a deposited film deposited on the input-side lower electrode and the base material formed on the substrate, and is bridged so as to cross a groove provided by removing the base material. 2. The piezoelectric thin film transformer according to claim 1, wherein the piezoelectric thin film transformer has the structure described above.   The first and second vias that electrically connect the input side electrode and the input side electrode respectively formed above and below the driving unit and the upper and lower surfaces of the driving unit are mechanical resonance of the piezoelectric body. The piezoelectric thin film transformer according to claim 1, wherein the piezoelectric thin film transformer is provided at a node. The output-side wiring electrically connected to the output-side electrodes formed on the side end portions of the power generation unit through vias has a structure in which the piezoelectric body is physically suspended from above. The piezoelectric thin film transformer according to any one of claims 1 to 3 . The substrate, as claimed in any one of claims 1, wherein a peripheral circuit including at least one control circuit for controlling the drive circuit or drive to drive the piezoelectric element is formed to the 4 Piezoelectric thin film transformer. A method of manufacturing a piezoelectric transformer having a drive unit and a power generation unit,
Forming an input-side lower electrode structure on a substrate in a region where the driving unit is formed ;
Forming a base material on a substrate in a region where the power generation unit is formed;
Depositing a thin film to be a piezoelectric body on the lower electrode on the input side and the base material ;
Processing the thin film to form a piezoelectric body;
Forming an input-side upper electrode wiring structure, an output-side left and right-side electrode wiring structure in the piezoelectric body;
Removing the underlying material below the piezoelectric body to form a cantilever bridge structure,
Depositing a thin film comprising the piezoelectric to the input side lower electrode and the base material, a step of orienting controlled to have a different orientation between the driving unit and the power generating unit,
The orientation control is performed by providing the base material having a different orientation of the thin film from that of the lower electrode on the input side in a region where the power generation unit is formed , and utilizing the base dependency of the orientation of the thin film. A method of manufacturing a piezoelectric thin film transformer, which is characterized.

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