JP2004282967A - Semiconductor electrostatic motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor electrostatic motor which rotates uniformly at a high speed by a simple step by suppressing the flowing out of a charge from the first impurity adding part 1b of a movable element to a semiconductor substrate 1a of the movable element by the channel on the surface of the semiconductor substrate to become a cause for bringing about a rotating unevenness. <P>SOLUTION: The entirety or at least the part of the surface of the semiconductor substrate 1a of the p-type movable element except the first impurity adding part 1b of the movable element of an n-type semiconductor of an electron supply source is formed as a p-type high concentration impurity adding part. A channel formation for deteriorating rotating characteristics is suppressed or made harmless. During the operation of the semiconductor electrostatic motor, the charge does not flow out from the first impurity adding part 1b of the movable element of the electron supply source. Thus, the semiconductor electrostatic motor which can rotate at a high speed and which does not have a rotating unevenness can be provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rotary type semiconductor electrostatic motor utilizing Coulomb force acting on electric charges, which is a semiconductor electrostatic motor capable of high-speed rotation without uneven rotation.
[0002]
[Prior art]
With the advance of microfabrication, research on using a semiconductor electrostatic motor as a microactuator has been actively conducted. A semiconductor electrostatic motor is composed of a movable body and a stator each having an electrode portion or an impurity-added portion, and uses a Coulomb force acting between the charges in the respective impurity-added portions or between the charge in the impurity-added portion and the electrode portion. It is driven at high speed (for example, see Non-Patent Document 1).
[0003]
FIG. 5 is a longitudinal sectional view passing through a center of rotation for explaining an example of a conventional semiconductor electrostatic motor. FIG. 6 is a top view for explaining an embodiment of a movable body of a conventional semiconductor electrostatic motor. FIG. 7 is a top view for explaining an embodiment of another movable body of the conventional semiconductor electrostatic motor. The shape of the stator 2 shown in FIG. 5 shows a cross section taken along line AA of the stator shown in FIG. 6 or FIG. Hereinafter, the structure and operation of an example of a conventional semiconductor electrostatic motor will be described.
[0004]
The conventional semiconductor electrostatic motor shown in FIGS. 5 and 6 has a disk-shaped movable body 1 formed by processing a semiconductor substrate made of an intrinsic semiconductor, a concentric circle formed by a stator insulator 2a and a stator electrode 2b. -Shaped stator 2, lower bearing 3 and upper bearing 4 made of a material such as a glass substrate which is an insulator, which is difficult for electric charge to flow in and out, a cylindrical steel shaft 5, a molded part 6 which is an insulator, and an insulator 7 It is composed of The stator 2 includes a concentric stator insulator 2a made of a shell or the like as an insulator, and a stator electrode 2b as a conductor provided on the surface of the insulator.
[0005]
A cylindrical shaft 5 is embedded in the center of the disk-shaped movable body 1, and both are integrated in a frame shape. The shaft 5 is supported by the lower bearing 3, and the center of the upper bearing 4 is a shaft 5. A hole larger than the diameter of the shaft 5 is drilled, and the upper part of the shaft 5 is located in the hole. A stator 2 is concentrically arranged between the upper bearing 4 and the lower bearing 3 so as to surround the disk-shaped movable body 1. Glued.
[0006]
The lower side of the shaft 5 is often conical in order to reduce the contact resistance with the lower bearing 3.
[0007]
Further, a plurality of first impurity-added portions 1b of the movable body made of an n-type high-concentration layer are arranged at equal intervals on the outer peripheral surface of the disk of the movable body 1.
[0008]
The electrode portions 2b of the stator are arranged at equal intervals between the inner peripheral side surface of the insulator portion 2a of the stator corresponding to the first impurity-added portion 1b of the movable body and the middle. That is, the number of the electrode portions 2b of the stator is twice the number of the first impurity-added portions 1b of the movable body (for example, see Patent Document 2).
[0009]
FIG. 4 is a diagram for explaining the operation of an example of a conventional semiconductor electrostatic motor.
FIG. 4 is a view of the movable body 1 and the electrode portion 2b of the stator viewed from above. Hereinafter, the rotation operation of the semiconductor electrostatic motor when the first impurity-added portion 1b of the movable body is an n-type high concentration layer will be described with reference to the drawing.
[0010]
A positive potential is applied to every other electrode portion 2b of the stator, and a negative potential is applied to the electrode portion 2b of the stator therebetween. Electrons, which are majority carriers in the first impurity-added portion 1b of the movable body formed by the n-type high-concentration layer, receive a repulsive force from the electrode portion 2b of the stator having a negative potential, and at the same time, the electrode portion 2b of the stator having a positive potential. The movable body 1 rotates in the direction of the arrow in FIG.
[0011]
The electrons, which are majority carriers in the first impurity-added portion 1b of the movable body formed by the n-type high-concentration layer, are biased toward the electrode portion 2b of the stator having a positive potential. Since the ionized acceptor of the first impurity-added portion 1b of the movable body, that is, the ionized n-type diffusion impurity (for example, phosphorus) is a fixed charge, its position is fixed and cannot move in the negative electrode direction.
Therefore, the Coulomb force acting on the majority carrier electron group becomes larger than the Coulomb force acting on the ionized acceptor atom group, so that the entire first impurity-added portion 1b of the movable body composed of the n-type high-concentration layer is on the positive potential electrode side. Electrically attracted to
[0012]
Thereafter, no voltage is applied to all the stator electrode portions 2b until the first impurity-added portion 1b of the movable body first passes through the front surface of the stator electrode portion 2b applied with a positive potential. The movable body 1 continues to rotate in the rotational direction due to inertia.
[0013]
After the movable body 1 passes in front of the electrode portion 2b of the first stator in the rotation direction, a voltage opposite to the above potential is applied to the electrode portion 2b of each stator. Due to the change in the voltage polarity, the movable body 1 further rotates in the above-described rotation direction.
[0014]
Along the clockwise direction, there are a stator electrode portion 2b of a positive potential and a stator electrode portion 2b of a negative potential. If there is a first impurity-added portion 1b of the movable body therebetween, the movable body 1 has a negative potential. From the positive potential electrode direction, and counterclockwise. Along the counterclockwise direction, there are a positive potential stator electrode portion 2b and a negative potential stator electrode 2b, and if the first impurity-added portion 1b of the movable body is between them, the movable body 1 has a negative potential. To the positive potential electrode direction, clockwise.
[0015]
Therefore, in order to make the rotation direction constant, the positional relationship between the electrode portion 2b of the positive-potential stator, the electrode portion 2b of the negative-potential stator, and the first impurity-added portion 1b of the movable body located therebetween is rotated. Needs to be confirmed and adjusted before starting.
[0016]
As is presumed from the above operation principle and the structure shown in FIG. 4, the first impurity-added portion 1b of the movable member and the semiconductor substrate portion of the movable member are affected by the voltage applied between the electrode portions 2b of the adjacent stators. A forward bias is applied to the junction 1a. As described above, the first impurity-added portion 1b of the movable body is an n-type. When the semiconductor substrate portion 1a of the movable body is an n-type intrinsic semiconductor, the electric charge in the first impurity-added portion 1b of the movable body is attracted to the electric field, and the movable body is moved from within the first impurity-added portion 1b of the movable body. Is diffused into the semiconductor substrate portion 1a and hardly contributes to rotation.
[0017]
Theoretically, there is no n-type or p-type in intrinsic semiconductor, but in reality, a perfect intrinsic semiconductor cannot be made, and the conventional example uses an intrinsic semiconductor for the purpose of using a high-resistance semiconductor. Since it is used, an n-type semiconductor having an impurity concentration close to that of the intrinsic semiconductor is called an n-type intrinsic semiconductor.
[0018]
When the semiconductor substrate portion 1a of the movable body is a p-type intrinsic semiconductor, the charge in the first impurity-added portion 1b of the movable body is contributed to the positive electrode portion 2b of the stator. At this time, a forward bias is applied to the pn junction closer to the positive stator electrode portion 2b with respect to the pn junction between the first impurity-added portion 1b of the movable member and the semiconductor substrate portion 1a of the movable member. .
[0019]
However, due to the barrier of the pn junction, the electric charge in the first impurity-added portion 1b of the movable body exceeds the pn junction between the first impurity-added portion 1b of the movable body and the semiconductor substrate 1a of the movable body. The amount of the movable body diffused into the semiconductor substrate portion 1a is smaller than that in the case of the n-type intrinsic semiconductor which forms an n / n-type junction.
[0020]
The first impurity-added portion 1b of the movable body that acts on the voltage of the stator 2 is preferably an n-type high concentration layer. Therefore, the intrinsic semiconductor substrate of the movable body is preferably a p-type intrinsic semiconductor. However, in a semiconductor manufacturing process, a p-type semiconductor surface is easily inverted to n-type due to ion contamination with sodium or the like, and a channel is formed in which electrons flow. Therefore, during the rotation operation, the electrons acting on the voltage of the stator 2 flow out of the surface of the first impurity-added portion 1b of the movable body into the channel and do not contribute to the rotation.
[0021]
In order to improve the problem of the outflow of charges from the first impurity-added portion 1b of the movable body, the semiconductor substrate portion 1a of the movable body between the first impurity-added portions 1b of the movable body is replaced with the movable body 1. There is a conventional embodiment in which the side surface is removed in the center direction.
[0022]
FIG. 7 is a view showing an embodiment of another movable body of the conventional semiconductor electrostatic motor based on this concept (for example, see Patent Document 2). Although this method is considered to be effective for outflow of charges beyond the pn junction, it is difficult to process the movable body 1 in this way, and the problem due to the channel of the semiconductor substrate still remains. .
[0023]
[Patent Document 1]
JP-A-63-161879 (page 4, FIG. 6)
[Patent Document 2]
JP-A-2-250682 (page 3, FIG. 2)
[Non-patent document 1]
"Pulse motor using impurity semiconductor", Journal of the Institute of Electrostatics, Vol. 15, No. 5, 1991, p. 381-p. 382.
[0024]
[Problems to be solved by the invention]
The present invention is intended to solve the above-described problem, and is intended to limit the rotation speed and cause a rotation unevenness from the first impurity-added portion 1b of the movable body to the semiconductor substrate portion of the movable body due to a channel on the surface of the semiconductor substrate. Provided is a semiconductor electrostatic motor that suppresses outflow of electric charge to 1a, rotates at high speed and uniformly in a simple process.
[0025]
[Means for Solving the Problems]
In order to solve the above problem, all or a part of the semiconductor substrate of the movable body except for the impurity-added part of the movable body which is a source of electrons is made a high-concentration impurity-added part, and the formation of a channel that deteriorates the rotation characteristics is suppressed or It is harmless.
Specifically, the invention according to claim 1 is a semiconductor substrate of a first conductivity type, wherein a plurality of first impurity-added portions of a second conductivity type are formed in contact with a surface of the semiconductor substrate. A semiconductor electrostatic motor comprising a body and a stator acting by voltage, wherein the impurity concentration of the first conductivity type of the semiconductor substrate is 10 ¹⁸ atom / cm ³ or more. It is.
The invention according to claim 2 is a semiconductor substrate of a first conductivity type, wherein a movable body having a plurality of first impurity-added portions of a second conductivity type formed in contact with a surface of the semiconductor substrate; A semiconductor static motor comprising an operating stator and a second impurity addition of a first conductivity type having a higher concentration than the semiconductor substrate in contact with a surface of the semiconductor substrate of the adjacent first impurity addition portion. A semiconductor electrostatic motor characterized by having a portion.
According to a third aspect of the present invention, there is provided the semiconductor electrostatic motor according to the second aspect, wherein an impurity concentration of the second impurity-added portion is 10 ¹⁸ atom / cm ³ or more.
The invention according to claim 4 is the semiconductor electrostatic motor according to any one of claims 1 to 3, wherein the first conductivity type is a p-type.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a longitudinal sectional structural view for explaining a first embodiment of the present invention. FIG. 3 is a longitudinal sectional view passing through the center of rotation of the semiconductor electrostatic motor. FIG. 2 is a top view of the movable body for explaining the first embodiment of the present invention. The shape of the stator 2 shown in FIG. 1 shows a cross section taken along line AA of the stator shown in FIG. Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
[0027]
The semiconductor electrostatic motor of the present invention includes a disk-shaped movable body 1, a stator 2 arranged concentrically, a lower bearing 3, an upper bearing 4, and a cylindrical shaft 5. Further, the stator 2, the lower bearing 3, and the upper bearing 4, which are arranged concentrically, are bonded and electrically insulated by a mold portion 6 and an insulator 7.
[0028]
A cylindrical shaft 5 is embedded in the center of the disk-shaped movable body 1 and is formed in a frame shape. The shaft 5 is supported by the lower bearing 3, and the upper bearing 4 has a diameter larger than that of the shaft 5 at the center. A large hole is drilled and the top of the shaft 5 is located in this hole.
[0029]
The shaft 5 has a conical lower side in order to reduce the contact resistance with the lower bearing 3. The material is abrasion-resistant steel or ceramic. The lower bearing 3 and the upper bearing 4 may be insulators, but use a conductor such as a semiconductor such as metal or silicon or a semi-insulator so as not to accumulate charges.
[0030]
The use of a wear-resistant silicon semiconductor has the advantage that the rotation is stable for a long period of time, and wirings and drive circuits can be formed in or on the silicon semiconductor substrate.
[0031]
FIG. 2 is a top view of the movable body 1 for explaining the first embodiment of the present invention. The movable body 1 is formed of a disk-shaped p-type semiconductor substrate. This semiconductor substrate is preferably a single crystal of a silicon semiconductor, but may be a polycrystal.
[0032]
The concentration of the p-type impurity in the p-type semiconductor substrate is higher than or equal to 10 ¹⁸ atoms / cm ³ so that the surface of the semiconductor substrate is not inverted to form a channel.
[0033]
First, a thermal oxide film is formed in a high-temperature oxidizing atmosphere containing water vapor and oxygen on the entire surface of a p-type semiconductor substrate in which a hole for attaching the shaft 5 is formed in the center.
[0034]
Next, a window for diffusion is formed on the peripheral side surface of the semiconductor substrate and on the upper and lower surfaces in contact with the side surface by photo-etching using hydrofluoric acid. These windows are formed at four places, equally spaced on the side.
[0035]
An n-type impurity is diffused from the diffusion window to form a first impurity-added portion 1b of the movable body. Specifically, phosphorus is deposited on a diffusion window of a semiconductor substrate using phosphorus oxychloride using an oxide film as a mask and diffused in a high-temperature dry oxygen atmosphere. The surface concentration of the impurities in this diffusion layer is 5 × 10 ¹⁹ atoms / cm ³ , and the diffusion depth is 5 μm.
[0036]
Due to this diffusion, the movable body becomes a region of the first impurity-added portion 1b of the movable body that is an n-type diffusion region and a semiconductor substrate portion 1a (p-type) of the movable body that is a p-type semiconductor excluding this region. Divided. The first impurity-added portion 1b of the movable body, which is an n-type diffusion region, is a supply source of electric charge acting on the potential of the stator 2.
[0037]
Although not shown in FIGS. 1 and 2, the oxide film left on the semiconductor substrate is a good protective film containing phosphorus in the oxide film, and thus is used without being removed.
[0038]
FIG. 3 is a top view of a movable body for explaining a second embodiment of the present invention. The shape of the stator 2 shown in FIG. 1 shows a cross section taken along the line AA of the stator shown in FIG. Since the structure is the same as that of the first embodiment except for the diffusion structure of the movable body, the diffusion structure of the movable body according to the second embodiment of the present invention will be described below with reference to FIG.
[0039]
The movable body 1 is formed of a disk-shaped p-type semiconductor substrate. This semiconductor substrate is preferably a single crystal of a silicon semiconductor, but may be a polycrystal.
[0040]
The concentration of the p-type impurity in the p-type semiconductor substrate is set to 10 ¹⁴ atoms / cm ³ . Since the diffusion layer for channel prevention (the second impurity-added portion 1c of the movable body) is separately manufactured, it is not necessary to have a high concentration as in the first embodiment. Since the concentration of the p-type impurity is relatively low, the holes in the p-type region do not unnecessarily act on the stator 2, and there is an advantage that the element can be easily designed.
[0041]
First, a thick thermal oxide film is formed in a high-temperature oxidizing atmosphere containing water vapor and oxygen on the entire surface of a p-type semiconductor substrate in which a hole for attaching the shaft 5 is formed in the center.
[0042]
Next, a window for diffusion is formed on the peripheral side surface of the semiconductor substrate and on the upper and lower surfaces in contact with the side surface by photo-etching using hydrofluoric acid. These windows are formed at four places, equally spaced on the side.
[0043]
An n-type impurity is diffused from the diffusion window to form a first impurity-added portion 1b of the movable body. Specifically, phosphorus is deposited on the diffusion window portion of the semiconductor substrate using phosphorus oxychloride using a thick oxide film as a mask and diffused in a high-temperature oxidizing atmosphere. An oxide film is formed on the surface of the diffusion window. The impurity has a surface concentration of 5 × 10 ¹⁹ atoms / cm ³ and a diffusion depth of 5 μm.
[0044]
Next, the surface of the p-type semiconductor substrate excluding the first impurity-added portion 1b of the movable body manufactured by diffusing the n-type impurity, that is, at least a part of the oxide film on the surface of the semiconductor substrate portion 1a of the movable body Is removed, and a window for p-type impurity diffusion is opened. As in the case of diffusing the n-type impurity, the treatment is performed by using a photograph and a hydrofluoric acid-based etchant.
[0045]
Boron, which is a p-type impurity, is diffused from the diffusion window by using ion implantation to form a second impurity-added portion 1c of the p-type movable body. The surface concentration of this diffusion layer is 10 ¹⁸ atom / cm ³ or more, and the diffusion depth is 7 μm, which is slightly deeper than the first impurity-added portion 1b of the 1 to n-type movable body.
[0046]
Due to the diffusion of boron and phosphorus, the movable body is an n-type diffusion region, the first impurity-added portion 1b of the movable body, the second impurity-added portion 1c of the p-type movable body, and the movable body excluding these portions. The first impurity-added portion 1b of the movable body, which is an n-type diffusion region, is a supply source of a charge acting on the potential of the stator 2. The second impurity-added portion 1c of the p-type movable body is a region where a channel is not formed, and is a channel stopper that does not continue the channel across this region.
[0047]
Although not shown in FIG. 3, the oxide film left on the semiconductor substrate is a good protective film containing phosphorus and boron in the oxide film, and thus is used without being removed.
[0048]
Since the channel is stopped by the region of the second impurity-added portion 1c of the p-type movable body, outflow of electrons is stopped during the rotation operation, and high-speed rotation without rotation unevenness is obtained.
[0049]
The number of first impurity-added portions 1b of the movable body, which is an n-type diffusion region and a source of electrons, is four in the present embodiment, but may be any number as long as it is two or more. Absent.
[0050]
Although the first impurity-added portion 1b of the movable body and the second impurity-added portion 1c of the movable body are diffused from the peripheral side surface of the semiconductor substrate and the upper and lower surfaces in contact with the side surface, examples have been shown. It is also possible to diffuse with a combination of two surfaces each.
[0051]
The example in which the second impurity-added portion 1c of the p-type movable body forms two regions between the first impurity-added portions 1b of the adjacent movable body has been described. It may be. The example in which the second impurity-added portion 1c of the p-type movable body is diffused from the peripheral side surface of the substrate and the upper surface and the lower surface in contact with the side surface has been described. Can also be spread.
[0052]
The semiconductor substrate portion 1a of the movable body is preferably made of silicon because it is easy to manufacture, but a semiconductor material such as GaAs or SiC can also be used.
[0053]
Although a semiconductor substrate having a first conductivity type of p-type is used, when the movable body 1 is protected by a resin film, negative charges are easily induced on the semiconductor surface. In such a case, it is preferable to use an n-type as the first conductivity type. A concentration of 10 ¹⁸ atoms / cm ³ or more is required to achieve the effect as a channel stopper as in the p-type.
[0054]
【The invention's effect】
According to the present invention, by preventing or stopping the formation of a channel on the surface of the semiconductor substrate, electric charge flows out of the first impurity-added portion 1b of the movable body that is a supply source of electrons during operation of the semiconductor electrostatic motor. Thus, a semiconductor electrostatic motor capable of high-speed rotation and having no rotation unevenness can be provided.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional structural view for explaining a first embodiment of the present invention.
FIG. 2 is a top view of the movable body for explaining the first embodiment of the present invention.
FIG. 3 is a top view of a movable body for explaining a second embodiment of the present invention.
FIG. 4 is a diagram for explaining an operation of an example of a conventional semiconductor electrostatic motor.
FIG. 5 is a longitudinal sectional view passing through a center of rotation for explaining an example of a conventional semiconductor electrostatic motor.
FIG. 6 is a top view for explaining an embodiment of a movable body of a conventional semiconductor electrostatic motor.
FIG. 7 is a top view for explaining an embodiment of another movable body of the conventional semiconductor electrostatic motor.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 movable body 1a movable body semiconductor substrate section 1b movable body first impurity added section 1c movable body second impurity added section 2 stator 2a stator insulator section 2b stator electrode section 3 lower bearing 4 Upper bearing 5 Shaft 6 Mold part 7 Insulator

Claims (4)

A semiconductor comprising a first conductive type semiconductor substrate, a movable body having a plurality of second conductive type first impurity-added portions formed in contact with a surface of the semiconductor substrate, and a stator acting by voltage. An electrostatic motor, wherein the semiconductor substrate has a first conductivity type impurity concentration of 10 ¹⁸ atoms / cm ³ or more. A semiconductor comprising: a first conductive type semiconductor substrate, a movable body having a plurality of second conductive type first impurity-added portions formed in contact with a surface of the semiconductor substrate; and a stator acting by voltage. An electrostatic motor, wherein there is a second impurity doped portion of a first conductivity type having a higher concentration than the semiconductor substrate in contact with a surface of the semiconductor substrate of the adjacent first impurity doped portion. Semiconductor electrostatic motor. ^3. The semiconductor electrostatic motor according to claim 2, wherein the impurity concentration of the second impurity-added portion is equal to or higher than 10 ¹⁸ atom / cm ^{3. 4} . 4. The semiconductor electrostatic motor according to claim 1, wherein the first conductivity type is a p-type. 5.

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