JPH01312485A - Electrostatic capacitor type ultrasonic wave transducer - Google Patents

Abstract

PURPOSE:To increase the insulation breakdown strength of an interlayer insulating film and to form a highly sensitive element by forming a lower electrode, forming an upper electrode comprising a conductor thin film through an insulator thin film and a gas cell that is formed on a hole on said lower electrode, and providing a vibrating film for which the upper electrode is formed. CONSTITUTION:A hole 103 is provided in the surface of a semiconductor silicon substrate 101. A lower electrode 102 comprising a diffused layer is provided on the surface of the substrate 101. An insulator thin film 104 is formed on the lower electrode 102. A gas cell 107 is formed on the hole 3. An upper electrode 105 comprising a conductor thin film is formed through the thin film 104 and the gas cell 107. The upper electrode 105 is formed for a vibrating film 106. Thus, an electrostatic capacitor type ultrasonic wave transducer is formed. The upper electrode 105 and the substrate 101 are grounded. A signal source 301 to which a DC bias 303 is connected in parallel is connected to the n-type diffused layer 102 which is to become the lower electrode. As a result, insulation breakdown does not occur even if the DC bias voltage of 100V is applied, and the element can be obtained at the very excellent yield rate.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention can be used to equip robots and various industrial equipment to measure the distance between objects that are relatively close to each other, or to use phased array processing to This invention relates to a new capacitive ultrasonic transducer for recognizing the thickness and shape of an object by visualizing its ultrasonic distance signal.

(Prior Art) In recent years, inexpensive and high-performance microcomputers have become widespread, and by using them, automation or robotization is progressing in various industrial fields. However, robots and automatic devices currently in practical use have a certain shape,
Currently, it is only possible to lift or carry objects of a certain size or weight, or to perform processing or assembly operations using a certain program.

On the other hand, due to the diversification of consumer groups, there is a strong tendency towards high-mix, low-volume production, and the FMS (Flexible Manufacturing System)
There is a call for the development of an automation technology called ``Uring System''. In this trend of automation, robots and automatic machines need to be equipped with various sensors to replace human sense organs, and to take quick and accurate actions based on the information. When a robot wants to pick up an object, it first finds the object using a visual sensor, then approaches the object using a proximity sensor, and finally uses information from a tactile sensor to determine the object's hardness and grip. Know where you are and pick up the object without dropping it. Among these sensors, proximity sensors obtain short-range distance information that cannot be captured by visual sensors, and those that use ultrasonic waves are considered suitable for distance measurement accuracy. Conventionally, PZT was used as this type of ultrasonic transducer.
There are many products on the market that utilize the resonance of piezoelectric materials such as lead zirconate titanate (lead zirconate titanate), but they have the drawback of narrow frequency characteristics. In addition, as an ultrasonic transducer using capacitance, for example, Japanese Patent Application No. 60-289290 or the proceedings of the IEEE 1986 Ultrasonic Symposium held in 1986 (IEEE 1986 Ult.
rasonics SymposiumProceed
ing) pages 559 to 562, and the Transducer 87 Digest held in 1987 (Tra
nsducers '87 Digest of Te
Chnical Papers) pages 414 to 417
There is a new proposal by Higuchi, Suzuki, Taniyo et al. described in the page. Figure 6 shows its typical structure.

In the figure, 101 is a silicon substrate, 103 is a hole for forming an air pocket 107 formed by silicon anisotropic etching, and 605 is an AI lower electrode. 604 is a CVD silicon oxide film, and 106 is a polyester film provided with an Al upper electrode 105 formed of a vapor-deposited film of A1. Its operating principle is similar to that of so-called condenser speakers and condenser microphones. That is, when a DC bias of approximately 30V is applied between the Al upper electrode 605 and the A1 upper electrode 105 and an AC signal is applied, the polyester film 106 vibrates, and the spring action of the air trapped in the air reservoir 107 causes a superfluid to be released into the air. When a sound wave is transmitted and an ultrasonic wave enters from the outside, the polyester film 106 vibrates due to the pressure change, and the capacitance of the pair of capacitors formed by the Al upper electrode 105 and the Al upper electrode 605 changes. It is possible to receive ultrasonic signals by converting them into electrical signals.

(Problems to be Solved by the Invention) The conventional capacitive ultrasonic transducer has been described above using an example. This type of ultrasonic transducer allows the amplification section and signal processing section to be formed on the same silicon substrate, and the frequency band can be controlled by changing the size of numerous holes precisely formed on the silicon surface. It has the excellent feature of being able to

However, first, the transmitting sensitivity and receiving sensitivity of this type of sensor are proportional to the DC bias, but
Since the dielectric strength of the CVD silicon oxide film shown in No. 4 is not very good, it has the disadvantage that it is impossible to apply a large DC bias.

Second, when the Al upper electrodes 605 are arranged in an array,
There is a difference in the surface between the part where the A1 lower electrode 605 is present and the part where it is not present, and a small air pocket is created between the adjacent electrodes, as shown by 607 in the figure, and the ultrasonic waves emitted from this part are affected by the influence between the adjacent electrodes. phase crosstalk occurs. Therefore, when attempting to reproduce a distance image of an object using ultrasonic waves by performing phased array processing, there is a drawback that a high-quality image cannot be obtained. What is phased array processing? Ultrasonic waves are transmitted from each ultrasonic transducer that makes up the array to the target object, and each transducer receives the reflected ultrasonic waves and converts them into electrical signals. iOnobe synthesis to obtain a distance image.

The object of the present invention is to eliminate the drawbacks of the above-mentioned prior art and to provide an ultrasonic lancet with high sensitivity and suppressed crosstalk.
- To provide a new structure for the server.

(Means for Solving the Problems) According to the present invention, there is provided a lower electrode consisting of a diffusion layer provided on the surface of a semiconductor substrate having a hole in the surface, an insulating thin film on the lower electrode, and an insulating layer formed on the hole. A capacitive ultrasonic transducer is obtained which is characterized in that it includes a vibrating membrane on which an upper electrode made of a conductive thin film is formed via a gas reservoir formed above.

Further, according to the present invention, there is obtained a capacitive ultrasonic transducer in which a plurality of the diffusion layers serving as lower electrodes are provided in an array to serve as an array electrode.

(Function) Since the ultrasonic transducer of the present invention utilizes a lower electrode formed of a diffusion layer, thermal silicon oxide, which has a much higher dielectric strength than a CVD silicon oxide film, is used as an interlayer insulating film with the upper electrode. By making it possible to use membranes, it is possible to create ultrasonic transducers with excellent transmitting and receiving sensitivities by simply changing the manufacturing process. Further, even when using an insulating film deposited by the CVD method, the dielectric strength can be improved because heat treatment can be performed after the film is deposited.

Furthermore, since the ultrasonic transducer with the structure of the present invention has a flat surface, unnecessary gas pockets are not created between adjacent electrodes, and therefore an ultrasonic image of an object can be reproduced by phased array processing. It is possible to reduce phase crosstalk.

(Example) FIG. 1 is a schematic cross-sectional view of an ultrasonic element for explaining a first example. In the figure, 101 is a p-type silicon substrate with (100) plane orientation, and 102 is an n-type diffusion layer to be a lower electrode. 103 is a hole for forming an air reservoir 107. 104 is a silicon thermal oxide film as an interlayer insulating film, and 106 is a polyester film with an Al upper electrode 105 deposited on one surface. This polyester film 10
6 is a vibrating membrane.

The manufacturing process for obtaining the ultrasonic transducer shown in FIG. 1 is shown in FIGS. 2(a) to 2(d). First, p-type (ioo)
A hole 103 for forming an air pocket 107 by forming a silicon thermal oxide film 110 on the surface of a silicon substrate 101 with a plane orientation.
A hole is made in the area where it should become, and the silicon is anisotropically etched using a hydrazine solution (FIG. 2(a)). Next, the silicon thermal oxide film 110 on the surface is removed, and phosphorus is diffused into the substrate surface in the portion including the hole 103 to form a highly concentrated n-type diffusion layer 103.
form. Next, a silicon thermal oxide film 104 is formed to serve as an interlayer insulating film with the upper electrode (FIG. 2(C)). Thereafter, a polyester film 1 with an A1 upper electrode 105 deposited on the back surface.
06 (Fig. 2(d)).

The ultrasonic transducer obtained as described above was driven by the circuit shown in FIG. 3, and the sound pressure during wave transmission was measured.

In other words, the signal source 30 has the A1 upper electrode 105 and the silicon substrate 101 grounded, and the DC bias 303 is connected in parallel.
1 is connected to the n-type diffusion layer 102 which becomes the lower electrode. As a result, even when a DC bias voltage of 100 V was applied, an element could be obtained with a very high yield without causing dielectric breakdown.

Next, the invention of claim 2 will be explained in detail. FIG. 4 shows a schematic sectional view thereof. In the figure, 402 is an n-type diffusion layer, which becomes an array electrode. The manufacturing method is the same as that of the first embodiment, so a description thereof will be omitted. The array electrode formed by the n-type diffusion layer 402 used in this embodiment has a regularly arranged rectangular pattern as shown in a plan view in FIG. When an ultrasonic image of an object was reproduced using the element thus obtained, an image of very good quality was obtained. This is because the array electrode is formed by a diffusion layer, so the small air pocket 60 in Fig. 6 (conventional example)
This is because there is no level difference that would cause 7.

In the above two embodiments, a polyester film with Al vapor-deposited on the back surface was used as the vibrating film, but other polymer films such as polyethylene film or polyimide film may be used without any problem. Alternatively, it may be simply a metal thin film, such as a titanium or gold thin film, or a ceramic thin film coated with another metal, such as an alumina or silicon nitride film. Further, in the above two embodiments, the side of the polyester film 106 on which the Al upper electrode 105 was deposited was used as the substrate side, but the side on which the Al upper electrode 105 was deposited may be placed on the front surface side. Further, although an n-type diffusion layer is used as the lower electrode and a p-type is used as the substrate, it goes without saying that the conductivity types may be opposite. Further, in the above two embodiments, 107 is an air pocket, but this is because the polyester membrane 106 is stretched in air, and it is clear that it can be stretched not only in air but also in nitrogen, inert gas, etc. .

(Effects of the Invention) As explained above, in the electrostatic capacitive ultrasonic transducer according to the present invention, it is possible to increase the dielectric strength voltage of the interlayer insulating film and create a highly sensitive element, which was a problem in the conventional technology. It is possible to make it with a simple process. Furthermore, since the surface can be made flat, crosstalk can be reduced even when elements are formed in an array.

[Brief explanation of the drawing]

1 and 2 are diagrams showing a first embodiment of the present invention. FIGS. 2(a) to 2(d) are schematic diagrams of the manufacturing process. FIG. 3 is a driving circuit diagram when the ultrasonic transducer thus obtained is used as a transmitter. FIG. 4 is a diagram showing a second embodiment of the present invention. FIG. 5 is a plan view showing the array electrode pattern of the diffusion layer in FIG. 4. FIG. 6 is a sectional view of a conventional capacitive ultrasonic transducer. 101 in the figure...Silicon substrate 102.402...
N-type diffusion layer 104...Silicon thermal oxide film 105...
・Al upper electrode 106...polyester film 107
...Air reservoir 604...CVD silicon oxide film 605...AI lower electrode 607...Small air reservoir. Patent applicant: Director of the Agency of Industrial Science and Technology Kozo Iizuka 1 Figure 1θ4. -, /I month 與る和he <PJM102, 72 type fox Kei layer Z Figure (b) (C) (d) * 3 Figure 3θ3. d 匡GOMO BA°IA MATA 卆 4 Figure 402.72 as a 5 meter 102.72 type 瓢恚卆ki b Figure 107, ri; narrative

Claims (2)

[Claims] (1) Through a lower electrode consisting of a diffusion layer provided on the surface of a semiconductor substrate having a hole on the surface, an insulating thin film on the lower electrode, and a gas reservoir formed above the hole,
A capacitive ultrasonic transducer comprising a vibrating membrane on which an upper electrode made of a conductive thin film is formed. (2) The capacitive ultrasonic transducer according to claim 1, wherein a plurality of said diffusion layers serving as lower electrodes are provided in an array to form an array electrode.