JP4749790B2 - Micromirror device and manufacturing method thereof, angle measurement method of micromirror device, and micromirror device application apparatus - Google Patents

Description

  The present invention relates to a micromirror device, a manufacturing method thereof, an angle measurement method of a micromirror device, and a micromirror device application apparatus.

Conventionally, many methods have been reported for driving micromirrors. For example, when electrostatic attraction is used, a voltage is applied to one part that is electrically and mechanically connected to the micromirror and the other part that is usually fixed. Drive by attractive force. As another example, when an electromagnetic force is used, a current is normally passed through a coil fixed to a mirror and driven by a Lorentz force that works by interaction with an external magnetic field. There are other methods using a piezoelectric actuator, a thermal actuator, and the like. Regardless of these driving methods, shearing stress due to torsion is generated in the torsion bar that supports the rotating mirror. For this reason, the sensor which detects a shear stress becomes effective.

  The resistance value of the piezoresistive element changes macroscopically when stress is applied. In the case of a semiconductor material such as silicon, the energy state of the conduction band and the valence band changes, and the number and mobility of carriers in the band change. Piezoresistive elements include normal gauges that detect normal stress and shear strain gauges that detect shear stress. In the optical scanner, shear stress is generated in the torsion bar in proportion to the mirror rotation angle.

  The basic structure is a single element gauge with four electrodes. Since a normal gauge requires a bridge composed of a plurality of elements, variations between elements and temperature unevenness cause errors. Since a shear strain gauge can be composed of only one element, it is less susceptible to variations. Since the structure is simple, it is advantageous when combined with a torsion bar. If a shear stress in a direction perpendicular to the current acts in a state where a current flows through the shear type strain gauge, a potential difference is generated in the direction perpendicular to the current. Since the generated potential difference is proportional to the shear stress, the mirror rotation angle can be measured.

  There are many demands for manipulating light beams such as laser beams in optical application technology. For example, a laser printer uses a highly controlled polygon mirror. The micromirror device is required to realize the same function with a small size and a high degree of integration. The characteristics of the micromirror device include variations from device to device, the presence of hysteresis, changes with time, etc., and thus cannot be used as they are for high-precision applications. In applications such as optical switches and optical cross-connects using micromirror devices, control is performed by monitoring a portion of the light. As the entire system including the optical system is required to have a control system, peripheral devices become larger, and wiring and control algorithms become complicated in an arrayed device. It may also impair the advantages of a highly integrated micromirror array.

  A technique for incorporating a certain type of sensor in a micromirror device is disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-267955 (Patent Document 1) and Japanese Translation of PCT International Publication No. 2003-529108 (Patent Document 2). In Patent Document 1, a sensor for detecting the position of the mirror is arranged under the mirror. This does not solve the problem of how to prepare and arrange the sensors to be combined, regardless of what detection method is employed, because a sensor separately prepared from the mirror device will be combined later. Japanese Patent Application Laid-Open No. 2004-228561 detects a mirror rotation angle by measuring a capacitance change of a vertical comb-shaped actuator that is one of electrostatic actuators.

Although the sensor using the capacitance signal has an advantage that the sensor structure can be easily manufactured, the detection drive circuit becomes complicated and the system becomes complicated due to the problem of parasitic capacitance. Particularly, it is not suitable for a system having a large number of devices such as a mirror array. On the other hand, a gauge using the piezoresistive effect has a simple detection circuit, and if the crystal orientation is used, the sensitivity to the vertical displacement of the mirror is low, and the sensitivity to rotation is high. In Japanese Patent Application Publication No. 2003-517631 (Patent Document 3), a micromirror device is applied to an optical fiber switch, and it is assumed that the mirror rotation angle is detected by some method. Furthermore, the device disclosed in “1 gauge type silicon pressure detection element” Yokogawa Technical Report (Non-Patent Document 1) is a shear type strain gauge that detects shear stress applied to a pressure sensor, and the mirror rotation angle is It is not applied to the sensor to detect.
JP 2002-267955 A Special table 2003-529108 gazette Special table 2003-517631 gazette "1 gauge type silicon pressure sensor" Yokogawa Technical Report Vol.32, No.3 (1988) 135.

Conventionally, the characteristics of the micromirror device include variations from device to device, the presence of hysteresis, changes over time, and the like, and there has been a problem that the mirror rotation angle cannot be accurately controlled. The present invention provides a micromirror device that can accurately control the rotation angle based on a gauge signal by integrating a gauge using a piezoresistance effect into a torsion bar that generates stress when the micromirror rotates. It is intended to provide.

  According to the present invention, in a micromirror device in which a silicon substrate is processed using a semiconductor anisotropic etching process, a mirror is formed on a torsion bar that is divided into p-type or n-type semiconductor regions in the thickness direction of the silicon substrate. A micromirror device having a structure provided with a shear type strain gauge utilizing a piezoresistive effect for measuring the rotation angle is obtained.

According to the present invention, there is obtained a micromirror device characterized in that the shear strain gauge using the piezoresistance effect is formed in a surface region of a torsion bar distant from the rotation center of the torsion bar cross section.
Further, according to the present invention, the p-type or n-type semiconductor region in the thickness direction of the silicon substrate is a micromirror or torsion bar that does not expose a pn junction on the anisotropically etched wall of silicon. A micromirror device characterized by the structure formed in the part is obtained.

According to the present invention, there can be obtained a micromirror device characterized by a structure in which a land for supplying a current to the shear strain gauge is divided into a plurality of parts.
According to the present invention, there can be obtained a micromirror device characterized by a structure in which a plurality of output voltage measurement locations of the shear strain gauge are installed at two or more locations that do not face each other.

Further, according to the present invention, a micromirror device having a structure in which a part or all of the surface of the micromirror device is covered with a protective film such as a silicon oxide film or a silicon nitride film can be obtained.
According to the present invention, there can be obtained a micromirror device characterized by a structure in which a thin film such as a silicon nitride film, amorphous silicon, or polysilicon is deposited on the whole or a part of the shear strain gauge.

According to the invention, the micromirror device is manufactured by performing silicon etching and sacrificial layer etching after preparing a part of the micromirror or torsion bar to be a p-type or n-type region. A method is obtained.
Further, according to the present invention, the output voltage measurement lands of the plurality of installed shear strain gauges are used to measure two or more output voltages, and a voltage equivalent to the output voltage of two opposing electrodes is obtained. A method of measuring the angle of the micromirror device is obtained, wherein the angle is calculated from the measured values of the output voltage at the two or more locations.

According to the invention, the current flowing through the shear strain gauge is time-modulated at a frequency higher than the resonance frequency of the mirror rotation of the device, and the output voltage signal is measured without affecting the mirror rotation angle. An angle measurement method for a micromirror device is obtained.
Furthermore, according to the present invention, an optical scanner, an optical scanner for endoscope, a laser display, a confocal microscope, a bar code reader, and a laser printer, wherein the rotation angle is controlled using the micromirror device. Thus, micromirror device application devices such as optical switches, optical attenuators, optical gain equalizers, and optical measuring instruments can be obtained.

According to the present invention, by incorporating a gauge utilizing the piezoresistive effect as an integral part of the micromirror device, the mirror rotation angle can be measured, the control based on the measurement signal can be performed, and the optical operation can be performed with high accuracy. can get. Conventionally, the micromirror device is mainly small, and it has been difficult to ensure the accuracy of the mirror rotation angle. For this reason, it has been difficult to apply to applications that require a high-precision mirror rotation angle. There is an effect to compensate for this weakness. Providing devices such as optical scanners, endoscope optical scanners, laser displays, confocal microscopes, barcode readers, laser printers, optical switches, optical attenuators, optical gain equalizers, and optical measuring instruments with controlled rotation angles it can.

The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a micromirror device incorporating a shear strain gauge using a piezoresistance effect according to an embodiment of the present invention. Reference numeral 1 denotes a mirror that reflects light. A material that obtains a high reflectance can be formed according to the application. Reference numeral 2 denotes a torsion bar that supports the mirror, and allows the mirror to rotate by twisting motion.

  Reference numeral 3 denotes a shear type strain gauge incorporated in a part of the torsion bar. A voltage signal is generated according to the shear stress generated inside the torsion bar. 4 is a wiring structure for electrically extracting the voltage signal generated in 3. Electrical wiring is realized with silicon mechanical structure. Reference numeral 5 denotes a land for taking out the voltage signal wired at 4 to the outside. Reference numeral 6 denotes a land for supplying a current necessary for operating the shear strain gauge.

  FIG. 2 is a diagram showing a schematic configuration in which the shear type strain gauge 3 of FIG. 1 is taken out and enlarged. The shear type strain gauge is arranged in the outer region away from the center of rotation of the torsion bar section by electrically dividing it into the p-type or n-type region. Reference numeral 20 denotes a p-type or n-type region formed on the torsion bar surface. 21 is an n-type or p-type region different from 20 formed in the torsion bar. Reference numeral 22 denotes a voltage or current source for supplying a current necessary for operating the shear strain gauge.

  As shown in FIG. 1, a current flows to 20 through the land 6. Since 22 is connected only to 20 or to reverse bias the relationship with 21, current is confined to the surface layer without leaking. The shear stress generated by the torsional motion of the torsion bar is increased in the outer region of the torsion bar, so that the gauge sensitivity can be increased. 23 is a voltage signal output terminal of the shear type strain gauge, and measures a voltage signal between 24a and 24b via 4 in FIG. Further, the shear strain gauge, the torsion bar, the wiring structure, and the land are not limited to the shapes described in the embodiments of FIGS. A metal material can be appropriately used for the land and the wiring.

  FIG. 3 shows an anisotropic etching of silicon where the pn junction at the boundary between 20 and 21 is produced by fabricating a p-type or n-type region in a part of a micromirror or torsion bar according to an embodiment of the present invention. It is a figure which shows the schematic structure which took out and expanded the micromirror device and the shear type | mold strain gauge 3 which were made not to be exposed to the wall surface which carried out. Further, the shape of the p-type or n-type region is not limited to that described in the embodiment of FIG.

  FIG. 4 shows the two locations opposite to each other as shown in FIGS. 1, 2, and 3 by changing the output measurement location of the shear strain gauge to three locations 24a, 24b, and 24 instead of two locations according to the embodiment of the present invention. It is equivalent by measuring a voltage signal from another land 5 and an intermediate voltage obtained by calculating from two voltage signals obtained from the two lands 5a and 5b without directly measuring the voltage of FIG. 5 is a diagram showing a schematic configuration in which a micro-mirror device that measures a voltage at a location opposite to the micro-mirror device and mechanically easily applies stress to a gauge portion and a shear-type strain gauge 3 taken out and enlarged.

  In this case, 5b and 6 are the same land. The voltage of 24a, 24b, and 24 is transmitted to 5a, 5b, and 5 without dropping, and the electrical resistance ratio is related to the electrical resistance while 24a to 24 are connected and 24 to 24b is connected. If the electric resistances are equal, the voltage 5a is V5a and the voltage 5b is V5b, so that the intermediate (V5a + V5b) / 2 represents a voltage signal at 24 opposing positions. This and the signal from the land 5 are compared and measured. Further, the number, shape and arrangement of the gauge output voltage signal lands are not limited to those described in the embodiment of FIG.

  FIG. 5 is a diagram showing a micromirror device capable of controlling the direction of an average total current flowing in a shear strain gauge and a schematic configuration enlarged by taking out the shear strain gauge 3 according to an embodiment of the present invention. . Currents for operating the shear strain gauges are supplied from the lands 6a and 6b, respectively. Further, the shape and arrangement of the region 20 for controlling the direction of the total current are not limited to those described in the embodiment of FIG.

  FIG. 6 is a diagram showing a schematic configuration of a micromirror device in which seven thin films are deposited in whole or in part and a shear type strain gauge 3 taken out and enlarged according to an embodiment of the present invention. Inside the torsion bar which is wide in the horizontal direction in the figure, the shear type strain gauge is arranged on the left side. The direction of the shear stress directly generated by the torsional motion of the torsion bar is the vertical direction in the figure, but a conjugate shear stress generated by balance of internal forces is generated. This is measured with a shear strain gauge.

  Further, the shape and arrangement of the shear strain gauge inside the torsion bar are not limited to those described in the embodiment of FIG.

  According to the present invention, a micromirror device is characterized in that a rotation angle can be measured by integrating a shear type strain gauge using a piezoresistance effect into a torsion bar of a micromirror made of silicon. The present invention can be applied to devices such as optical scanners, endoscope optical scanners, laser displays, confocal microscopes, barcode readers, laser printers, optical switches, optical attenuators, optical gain equalizers, and optical measuring instruments.

FIG. 1 is a diagram showing a schematic configuration of a micromirror device incorporating a shear strain gauge using a piezoresistance effect according to an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration in which the shear type strain gauge 3 of FIG. 1 is taken out and enlarged. FIG. 3 is a diagram showing a schematic configuration in which the micromirror device according to the embodiment of the present invention and the shear strain gauge 3 are taken out and enlarged. FIG. 4 is a diagram showing a schematic configuration in which the micromirror device according to the embodiment of the present invention and the shear strain gauge 3 are taken out and enlarged. FIG. 5 is a diagram showing a schematic configuration in which the micromirror device according to the embodiment of the present invention and the shear strain gauge 3 are taken out and enlarged. FIG. 6 is a diagram showing a schematic configuration in which the micromirror device according to the embodiment of the present invention and the shear strain gauge 3 are taken out and enlarged.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mirror 2 Torsion bar 3 Shear type strain gauge incorporated in torsion bar 2 4 Electric wiring structure for taking out output voltage signal of shear type strain gauge 3 5,5a, 5b Output voltage signal land of shear type strain gauge 3 6, 6a, 6b Land for flowing current to the shear strain gauge 3 7 Film deposited on the surface of the torsion bar 8 Torsional motion of the torsion bar accompanying mirror rotation 20 p-type or n-type region formed in the surface layer of the torsion bar 2 21 n-type or p-type region different from 20 formed on the torsion bar 2 22 voltage or current source for passing a current through the shear-type strain gauge 23 output terminals 24, 24a, 24b for the shear-type strain gauge voltage signal Gauge output voltage measurement point

Claims (7)

In a micromirror device that processes a silicon substrate using a semiconductor anisotropic etching process,
P-type and n-type semiconductor regions are stacked in the thickness direction of the silicon substrate on the portion of the torsion bar that supports the mirror of the silicon substrate,
In addition to providing a p-type or n-type semiconductor region on the surface side, a shear-type strain gauge using a piezoresistance effect that measures the rotation angle of the mirror,
The wiring structure for supplying current for operating the shear type strain gauge and the wiring structure for extracting the voltage signal generated by the shear type strain gauge also use the p-type or n-type semiconductor region on the surface side as wiring,
The current for operating the p-type or n-type shear strain gauge on the surface side is confined in the p-type or n-type semiconductor region on the surface side in the thickness direction of the substrate by applying a reverse bias in the thickness direction of the silicon substrate. A micromirror device characterized by that.
2. The micromirror device according to claim 1, wherein the shear type strain gauge using the piezoresistance effect is formed in a surface region of the torsion bar away from the mechanical rotation center of the torsion bar cross section. In the p-type or n-type semiconductor region divided in the thickness direction of the silicon substrate, the upper p-type or n-type semiconductor region is not exposed so that the p-type and n-type junction surfaces are not exposed on the anisotropically etched wall of silicon. 3. The micromirror device according to claim 1, wherein the semiconductor region is formed on the entire micromirror or a part of the torsion bar so as to be inside the lower n-type or p-type semiconductor region. The output voltage measurement location of the shear type strain gauge is provided in plural at two or more locations that are not opposed to the direction of the current for operating the shear type strain gauge. 2. The micromirror device according to item 1. The land for passing a current to the shear type strain gauge has a structure in which the land is divided into two or more locations, and the direction of the average current flowing to the shear type strain gauge can be controlled by passing the current from the plurality of lands. The micromirror device according to claim 1, wherein the micromirror device is a micromirror device. Two or more output voltages are measured using the output voltage measurement points of the plurality of installed shear strain gauges, and the voltage equivalent to the output voltage of two opposite points is obtained as the output voltage of the two or more points. The angle measurement method for a micromirror device according to claim 4, wherein the angle measurement method is obtained by calculating from the measured value. The rotation angle is controlled using the micromirror device, the optical scanner according to any one of claims 1 to 6, an optical scanner for endoscope, a laser display, a confocal microscope, Barcode reader, laser printer, optical switch, optical attenuator, optical gain equalizer or optical measuring instrument micromirror device application equipment.