CN114647077A - Integrated piezoresistive feedback electric heating type micro-mirror - Google Patents
Integrated piezoresistive feedback electric heating type micro-mirror Download PDFInfo
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- G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
- G02B26/0866—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting means being moved or deformed by thermal means
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Abstract
The invention discloses an integrated piezoresistive feedback electrothermal micromirror, and belongs to the technical field of micro-nano optical systems. The driver of the invention comprises a conventional driver and an island structure driver. The piezoresistive sensor with the angle sensing function is integrated on the micro mirror to detect the deflection posture of the micro mirror in real time, the posture information is fed back to the control center, and the control precision of the micro mirror is improved through piezoresistive feedback. In addition, by optimizing the stress distribution of the driver and the output of the piezoresistors, the temperature of a piezoresistor area is effectively reduced by insulating and isolating the piezoresistors, the thermal noise of the piezoresistors is further inhibited, and the feedback control precision of the piezoresistors on the electrothermal micromirror is further improved. The micromirror driver adopts a parallel symmetrical driver, can generate larger driving capability, and increases the vertical displacement range and the angle scanning range of the micromirror. The symmetrically distributed bridge resistors can suppress temperature drift caused by temperature difference to the maximum extent.
Description
Technical Field
The invention relates to an integrated piezoresistive feedback electrothermal micromirror, in particular to a feedback-controllable electrothermal micromirror capable of bearing high temperature, and belongs to the technical field of micro-nano optical systems.
Background
Microelectromechanical Systems (MEMS) micromirrors have been used in a variety of applications, such as biomedical imaging, optical switches, smart windows, and laser radar (LiDAR). Among various driving mechanisms of the MEMS micromirror, the piezoelectric driving and the electrostatic driving have advantages of fast speed and low power consumption, but the electrothermal bimorph driving performs better in terms of low driving voltage and high fill factor. In addition, the electrothermal bimorph can easily realize a MEMS micromirror with a large scanning angle range and a large piston displacement. However, due to the high temperatures required for large drive ranges and the use of ductile metals as the bimorph layer, the electro-thermal micromirror is prone to significant drift over time due to metal fatigue and creep, which requires a position sensing mechanism to correct for and enable use in applications requiring high precision control. The position sensing of the electrothermal micromirror has been studied in combination with techniques such as optical reflection, optical interference and inductive coupling. However, these methods require additional components, precise alignment, and specialized packaging, which greatly increases size and cost, making it nearly impossible to fabricate large arrays of electrothermal micromirrors with position sensing capability. Therefore, it is necessary to develop an electrothermal micromirror having an integrated position sensing function.
Disclosure of Invention
The invention mainly aims to provide an integrated piezoresistive feedback electrothermal micromirror, which integrates a piezoresistive sensor with an angle sensing function on the micromirror to detect the deflection attitude of the micromirror in real time, feeds the attitude information back to a control center and improves the control precision of the micromirror through piezoresistive feedback. In addition, by optimizing the stress distribution of the driver and the output of the piezoresistors, the temperature of a piezoresistor area is effectively reduced by insulating and isolating the piezoresistors, the thermal noise of the piezoresistors is further inhibited, and the feedback control precision of the piezoresistors on the electrothermal micromirror is further improved. The micromirror driver adopts a parallel symmetrical driver, can generate larger driving capability, and increases the vertical displacement range and the angle scanning range of the micromirror. The symmetrically distributed bridge resistors can suppress temperature drift caused by temperature difference to the maximum extent.
The purpose of the invention is realized by the following technical scheme.
The invention discloses an integrated piezoresistive feedback electrothermal micromirror, which comprises a frame, a micromirror, a driver, a piezoresistor, a metal lead and a metal electrode. The driver includes a conventional driver and an island structure driver.
The frame is a frame with a hollow middle part, an island-shaped structure horizontally extends from the inner side surface of the frame, a piezoresistor with an angle sensing effect is formed on the surface of the island-shaped structure through diffusion or doping, the island-shaped structure is detected through the piezoresistor and driven by a driver to generate motion state change, the deflection posture of the micromirror is detected in real time, the posture information is fed back to a control center, and the deflection precision of the micromirror is improved through the high-sensitivity piezoresistor feedback. The other end of the island-shaped structure is connected with a driver, and the driver is used for driving and supporting the micro lens. The micro lens is connected to the center of the frame through the connecting structure on the arm driver, which is beneficial to the symmetrical layout and the extension in the length direction of the arm driver. The metal lead and the metal electrode are arranged on the surface of the frame and used for applying loading voltage to the driver and the piezoresistors, the driver is heated to deform to drive the island-shaped structure to deform, the stress distribution of the driver is optimized, the piezoresistors are optimized to output, the temperature of a piezoresistor area is effectively reduced by isolating the piezoresistors in a thermal insulation mode when the voltage of the larger piezoresistors is output, the thermal noise of the piezoresistors is further suppressed, and the feedback control precision of the piezoresistors to the electric heating type micro-mirror is further improved.
Piezoresistive output is optimized by optimizing actuator stress distribution. The optimized rear driver comprises a spring connection mode and a direct connection mode according to the connection mode of the driver and the island-shaped structure.
Adopt the spring connection formula to the driver, electric heat formula micro-mirror adopts spring connection structure, and an insulating buffer is connected respectively at both ends about the driver, and insulating buffer links to each other with serpentine spring's one end, and the other end of spring and independent island structure constitute elastic system, and island structure forms the bridge type pressure drag that is used for detecting the micro-mirror motion state after being heated through diffusion or doping on the surface.
Adopt the lug connection formula to the driver, the electrothermal type micro mirror adopts direct connection formula connection structure, extend two cantilever beams respectively and pass through connection structure lug connection with the driver in the middle left side right-hand member on the frame, also be two cantilever beams symmetry in the left and right sides of island structure column structure, be favorable to the symmetric distribution of temperature, furthest's reduction temperature drift is to the influence that the pressure drag output brought, form the bridge type pressure drag that is used for detecting the cantilever beam motion state after being heated through diffusion or doping on the surface of cantilever beam, wherein pressure drag and pressure drag arrangement direction are perpendicular for the output of increase pressure drag.
In order to further facilitate the connection of the island-shaped structure and the driver, preferably, the frame is a rectangular frame with a hollow middle part, the inner side surface of the rectangular frame horizontally extends out of the island-shaped structure towards the center, so that the island-shaped structures are symmetrically distributed, one part of the island-shaped structures is used for current flowing in, and the other part of the island-shaped structures is used for current flowing out. The free end of the island-shaped structure is laterally connected with the driver to play a role in supporting the driver.
Further, the driver consists of six Bimorphh structures and a plurality of sections of silicon arms; the Bimorph structure and the silicon arm are prepared on the basis of a monocrystalline silicon layer. Bimorph3.1.1, bimorph 3.1.2, bimorph 3.1.4 are shown in accordance with the analysis of the document [ Wu L, Xie H.A comparative-shift-free and large-vertical-displacement electric reactor for scanning micromicror/lens [ C ]// TRANSDUCERS 2007 & 2007 International Solid-State Sensors, Actuators and microspheres conference. IEEE,2007:1075 & 1078 ], wherein the length of bimorph3.1.1 is 2 times the length of bimorph 3.1.2 and bimorph 3.1.4, in order to eliminate lateral displacement. The six-section bimorph has the same material composition except for the length, and the materials of the bimorph structure sequentially comprise Si, a lower layer insulating material, a heating resistor, an upper layer insulating material and metal from bottom to top, and deform when being heated. The silicon arm is made of Si, an insulating material, a heating resistor and an insulating material from bottom to top, wherein the heating resistor is a driver heating resistor. Insulation between silicon and metal is achieved through the Bimorph structure and the silicon arm layered layout, and the phenomenon that the Bimorph structure fails due to the fact that metal ions are accumulated to one end of the metal in the Bimorph structure due to the charge accumulation effect is avoided. By optimizing the thickness ratio of the bimorph materials of the driver, the scanning range of the micro-mirror can be effectively enlarged on the basis of improving the flexibility of the driver.
In addition, a metal resistor is not needed, because the monocrystalline silicon can form a heater directly through doping, and the dual functions of resistance heating and electric conduction are realized.
More preferably, the metal electrode and the lead are made of Al, Ag, Au, or Cu, and the metal resistor is made of Pt or W.
The insulating material is SiO2、PI、Si3N4。
The serpentine spring is made of Si, the insulating buffer area is made of silicon oxide, and the buffer area is connected with the cantilever beam structure through the serpentine spring structure.
The piezoresistive sensor is a high-temperature piezoresistive sensor, and in order to inhibit piezoresistive leakage current caused by temperature, an insulating groove is etched around the piezoresistive sensor during the preparation of the piezoresistive sensor, and then an insulating material is filled, so that heat insulation and leakage current inhibition are performed to the maximum extent, and the temperature range of the piezoresistive sensor is widened. Furthermore, the cantilever beam is made of silicon film, and the piezoresistive and silicon film are made of insulating material and are used for isolating the piezoresistive and the silicon film, so that the temperature of a piezoresistive region is effectively reduced through thermal insulation isolation of the piezoresistive, the thermal noise of the piezoresistive is further inhibited, and the feedback control precision of the piezoresistive on the electrothermal micromirror is further improved.
The invention discloses a method for manufacturing an electrothermal micromirror integrating piezoresistive feedback, which adopts a spring connection mode and comprises the following steps:
the method comprises the following steps: etching a slit with a certain depth On the front surface of an SOI (Silicon-On-Insulator) substrate by using photoresist as a mask and adopting an etching process, and then growing a layer of insulating material in the slit by adopting a thin film process for connecting a driver and a micro-lens;
step two: then growing an insulating thin layer on the substrate, then growing a heating resistor with a certain thickness, peeling to form the heating resistor of the driver, and preparing the insulating thin layer on the heating resistor for insulation;
step three: growing a layer of metal on the surface of the insulating thin layer, forming a reflecting surface on the mirror driver, forming electrodes around the frame structure, and forming each section of Bimorphh on the driver;
step four: preparing a piezoresistor with a certain thickness, and etching to form a driver and a mirror structure;
step five: growing an insulating thin layer with a preset thickness on the back of the substrate, etching a certain area, exposing Si, etching a cavity with a certain depth, etching the insulating layer of the middle area, etching the cavity until the buried oxide layer is etched, and forming a step with a certain thickness in the middle area and the periphery of the middle area;
step six: and spin coating a protective layer on the front surface of the substrate for protection, then etching silicon dioxide of the oxygen burying layer to release the device, and then scribing to obtain a single electrothermal micro mirror.
The invention discloses a method for manufacturing an electrothermal micromirror integrating piezoresistive feedback, which adopts a direct connection mode and comprises the following steps:
the method comprises the following steps: etching a slit with a certain depth On the front surface of an SOI (Silicon-On-Insulator) substrate by using photoresist as a mask and adopting an etching process, and then growing a layer of insulating material in the slit by adopting a thin film process for connecting a driver and a micro-lens;
step two: then growing an insulating thin layer on the substrate, then growing a heating resistor with a certain thickness, peeling to form the heating resistor of the driver, and preparing the insulating thin layer on the heating resistor for insulation;
step three: growing a layer of metal on the surface of the insulating thin layer, forming a reflecting surface on the mirror surface, forming electrodes around the frame structure, and forming each section of Bimorphh on the driver;
step four: preparing a piezoresistor with a certain thickness, and etching to form a driver and a mirror structure;
step five: growing an insulating thin layer with a preset thickness on the back of the substrate, etching a certain area, exposing Si, etching a cavity with a certain depth, etching the insulating layer of the middle area, etching the cavity until the buried oxide layer is etched, and forming a step with a certain thickness in the middle area and the periphery of the middle area;
step six: and spin coating a protective layer on the front surface of the substrate for protection, then etching silicon dioxide of the oxygen burying layer to release the device, and then scribing to obtain a single electrothermal micro mirror.
Has the advantages that:
1. the invention discloses an integrated piezoresistive feedback electrothermal micromirror, which integrates a piezoresistive sensor with an angle sensing function on the micromirror to detect the deflection attitude of the micromirror in real time, feeds back the attitude information to a control center, and improves the deflection precision of the micromirror through piezoresistive feedback. In addition, by optimizing the stress distribution of the driver and the output of the piezoresistors, the temperature of a piezoresistor area is effectively reduced by insulating and isolating the piezoresistors, the thermal noise of the piezoresistors is further inhibited, and the feedback control precision of the piezoresistors on the electrothermal micromirror is further improved.
2. The invention discloses an integrated piezoresistive feedback electrothermal micromirror, wherein a micromirror driver adopts a parallel symmetrical driver, so that the greater driving capability can be generated, and the vertical displacement range and the angle scanning range of the micromirror are enlarged. The symmetrically distributed bridge resistors can suppress temperature drift caused by temperature difference to the maximum extent.
3. The invention discloses an integrated piezoresistive feedback electrothermal micromirror, which realizes insulation between silicon and metal through a Bimorph structure and silicon arm layered layout, and avoids Bimorph structure failure caused by accumulation of metal in the Bimorph structure towards one end. By optimizing the thickness ratio between the bimorph materials of the driver, the flexibility of the micromirror is improved to expand the scanning range of the micromirror.
4. The invention discloses an integrated piezoresistive feedback electrothermal micromirror, wherein piezoresistance is a high-temperature piezoresistive sensor, piezoresistive leakage current caused by temperature can be inhibited, an insulating groove is etched around the piezoresistance during the preparation of piezoresistance, and then an insulating material is filled, so that the piezoresistive sensor is maximally insulated, the leakage current is inhibited, and the temperature range of the piezoresistive sensor is improved. The cantilever beam is of a silicon film, and the piezoresistive and the silicon film are made of insulating materials and are used for isolating the piezoresistors from the silicon film, so that the temperature of a piezoresistor area is effectively reduced through thermal insulation isolation of the piezoresistors, the thermal noise of the piezoresistors is further suppressed, and the feedback control precision of the piezoresistors on the electrothermal micromirror is further improved.
5. The invention discloses an integrated piezoresistive feedback electric heating micro mirror, which respectively provides a preparation method of the integrated piezoresistive feedback electric heating micro mirror by correspondingly adopting a spring connection mode and a direct connection mode, and can be manufactured at low cost and high efficiency.
Drawings
Fig. 1 is a schematic diagram of a basic structure of a piezoresistive feedback micromirror with a spring structure, wherein: fig. 1(a) is an overall schematic view of a spring-type structure, and fig. 1(b) is a close-up schematic view of a driver 3;
FIG. 2 is a schematic diagram of a basic structure of a piezoresistive feedback micromirror with a direct-connecting structure;
FIG. 3 is a schematic diagram of the locations of piezoresistors on a cantilever beam in a spring-type micromirror;
FIG. 4 is a graph of temperature versus drive voltage at the piezoresistive site Point A1 and at the actuator Point S1;
FIG. 5 is a graph of four-corner displacement versus driving voltage on a lens;
FIG. 6 is a graph of stress on a piezo-resistor versus drive voltage;
FIG. 7 is a graph of sensor output voltage versus drive voltage;
FIG. 8 is a graph of the relationship between micromirror deflection angle and piezoresistive output voltage;
FIG. 9 is a graph of stress at a piezoresistive versus piezoresistive output voltage;
FIG. 10 is a schematic diagram of the position distribution of piezoresistors in a micromirror with a direct-coupled structure and the connection manner with a driver;
FIG. 11 is a graph of temperature versus driving voltage at Point A1 and at Point S1 at piezoresistors in a spring-structured thermally actuated micromirror;
FIG. 12 is a graph of four corner point displacement on a lens versus drive voltage;
FIG. 13 is a graph of stress on a piezo-resistor versus drive voltage;
FIG. 14 is a graph of sensor output voltage versus drive voltage;
FIG. 15 is a graph of the relationship between micromirror deflection angle and piezoresistive output voltage;
FIG. 16 is a graph of the relationship between stress at the piezoresistors and piezoresistive output voltage;
wherein, 1-frame, 2-lead, 3-drive structure, 4-micro lens, 3.1 driver, 3.2-spring structure, driver, 3.1.1/3.1.2/3.1.4-Bimorph structure, 3.1.5-silicon arm, 3.1.3-island structure, 3.2.1-buffer region structure, 3.2.2-spring structure, 3.2.3-cantilever beam, 3.2.4-piezoresistance structure, 3.2.5-fixed anchor point is used for connecting frame and cantilever beam, 3.3-direct connection structure, 3.3.1-connecting piece, 3.3.2-cantilever beam, 3.3.3-transverse piezoresistance, 3.3.4-longitudinal piezoresistance.
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
The invention provides an integrated piezoresistive position sensing electric heating type micro mirror, which has two basic configurations, namely a piezoresistive feedback type micro mirror with a spring structure and a piezoresistive feedback type micro mirror with a direct connection structure.
Example 1:
as shown in fig. 1, the piezoresistive feedback thermal driving micromirror frame 1, the micromirror plate 4, the driver 3, the piezoresistance 3.2.4, and the metal wire 2 of the spring structure disclosed in this embodiment are shown.
The frame 1 is a rectangular frame with a hollow middle part, an island-shaped structure 3.1.3 horizontally extends from the inner side surface of the rectangular frame to the center, a piezoresistance 3.2.4 for detecting the motion state change of the driver 3.1 after being heated is formed on the surface of the cantilever beam 3.2.3 by diffusion or doping, the free end of the island-shaped structure is connected with the driver 3.1, and the driver 3.1 consists of six bimorph structures (3.1.1/3.1.2/3.1.4) and a plurality of sections of silicon arms 3.1.5 and is used for driving and supporting the micro-lenses; the Bimorph structure comprises Si, heating resistors (such as Pt, W and the like) and SiO in turn from bottom to top2The metal deforms when heated, and the material of the silicon arm 3.1.5 is divided into four layers, namely Si,Insulating material (e.g. SiO)2) Heating resistor (e.g. Pt), insulating material (e.g. SiO)2) Wherein the heating resistor provides a heat source for the driver 3.1.
The micromirror 4 is connected to the center of the frame 1 through the connecting structure 10 on the driver 3.1; the metal lead 2 and the metal electrode 3 are arranged on the surface of the frame and used for loading voltage to the driver 3.1, the driver 3.1 is heated and deformed to drive the island-shaped structure 9 to generate displacement, and then the output voltage of the cross-shaped piezoresistor 8 is changed, and the angle change of the micro-lens 4 is fed back through the voltage value.
In the electrothermal micromirror, the driver 3.1 drives the micromirror 4 to generate deflection or vertical motion by electric heating, so that the moving posture of the micromirror mirror can be detected by integrating piezoresistive sensors on the cantilever connected with the driver. Since the piezoresistance in fig. 1 works based on the piezoresistance effect, the working principle of the micromirror shown in fig. 1 is taken as an example to illustrate, and the working principle of the piezoresistance in fig. 2 is not described again.
In this embodiment, the relationship between the stress distribution of the piezoresistance and the displacement of the micromirror can be obtained by Comsol simulation.
Three conditions need to be met at the place where the piezoresistors are placed, namely, effective stress response, and even under the condition that the micro mirror is slightly displaced, the stress at the piezoresistors needs to be large enough to meet effective piezoresistor output; secondly, the piezoresistance part can effectively isolate the temperature, and even if the temperature of the driver is as high as 400-500K, the temperature of the piezoresistance part needs to be kept in an effective working state; thirdly, enough space is needed to place the piezoresistance.
In order to improve the high-temperature performance of the piezoresistance, a heat insulating layer (such as a silicon dioxide thin layer) is prepared on the island-shaped structure to isolate the leakage current generated by the piezoresistance at high temperature. The driver comprises a four-layer structure with Si and insulating material (such as SiO) from bottom to top2) Heating resistor (e.g. Pt, W, etc.), insulating material (e.g. SiO)2) And metal to electrically isolate the silicon from the heating resistor and the heating resistor from the metal (e.g., aluminum), wherein the thickness of the Pt and the insulating material is small enough to minimize the influence on the drive of the bimorph. The island structure is divided into three layers from the bottomFrom above, Si/insulating layer/piezoresistors are respectively, wherein the material of the cross-shaped piezoresistor is p-doped silicon.
It is noted that the verification only gives results under the specific parameters of this embodiment.
As shown in fig. 1(b), the piezoresistive feedback micromirror with spring structure can enhance the thermal insulation capability and piezoresistive sensitivity of the island structure, the left and right ends of the actuator are connected to a buffer region (the material can be silicon oxide but is not limited to materials with similar functions), and then connected to one end of a zigzag spring, the material of the spring is Si, and the other end of the spring is connected to a separate cantilever beam, as shown in fig. 1 (b). The resulting large displacement at the end of the actuator can be transferred through the spring to the cantilever beam, causing a change in the piezoresistive output voltage. In order to simplify the calculation, the frame structure of the micromirror is removed in the simulation, and at an input voltage of 0.5V, the temperature distribution on the micromirror is mainly concentrated on the driver that is thermally deformed, and the temperature at the piezoresistance is significantly decreased. Figure 4 shows the temperature Point S1 on the actuator and the temperature Point a1 at the piezoresistive, which differ by about 100K at an input voltage of 0.5V. The temperature drop is significant compared to the 3.1 scheme. FIGS. 13-16 are graphs of displacement of the micromirror, stress on the piezoresistors, and piezoresistive output voltage versus driving voltage, respectively.
In order to further analyze the piezoresistive sensing performance of the micromirror, a relation curve between piezoresistive output voltage and the deflection angle of the micromirror and the stress at the piezoresistive position is calculated, so that the angular Sensitivity and the stress Sensitivity are calculated, wherein the angular Sensitivity is SensitivityA22.45mV/(V DEG degree), and the stress Sensitivity is Sensitivityσ20.197mV/(V MPa), angular resolution R2＝Sensitivityσ2/SensitivityA20.08 °/MPa. That is, the pressure at the piezoresistance changes by 1MPa for every 0.08 deg. change of the micromirror.
As shown in fig. 2, the piezoresistive feedback micromirror with the direct connection structure makes the piezoresistive response more sensitive to the displacement and angle of the micromirror, two cantilever beams 3.3.2 extending from the frame are directly connected to the driver through a connection structure 3.3.1, and two rectangular cantilever beams 3.3.2 are symmetrically located at the left and right sides of the island-shaped structure 3.1.3, as shown in fig. 10.
Further verifying the specific temperature values, FIG. 11 shows the temperature variation on the actuator and piezoresistance as a function of input voltage. The temperature at the actuator, Point S1, and the temperature at the piezoresistors, Point a1, differ by about 60K at an input voltage of 0.5V. Fig. 12-14 are graphs of displacement of the micromirror, stress on the piezoresistors, and piezoresistive output voltage versus driving voltage, respectively.
In order to further analyze the piezoresistive sensing performance of the micromirror, the angular Sensitivity and the stress Sensitivity are calculated by calculating the relation curve between the piezoresistive output voltage and the deflection angle of the micromirror and the stress at the piezoresistive position, wherein the angular Sensitivity is SensitivityA310.56mV/(V DEG), and a stress Sensitivity of Sensitivityσ30.174mV/(V MPa), angular resolution R2＝Sensitivityσ2/SensitivityA20.016 degree/MPa. That is, the pressure at the piezoresistance changes by 1MPa every time the micromirror changes by 0.016 deg.
The embodiment also provides a preparation method of the electrothermal micro mirror integrating piezoresistive feedback, and a preparation method of the spring structure micro mirror and the direct connection structure micro mirror, which specifically comprises the following steps:
the method comprises the following steps: etching a slit with a certain depth (such as 2 μm depth) On the front surface of an SOI (Silicon-On-Insulator) substrate by using photoresist as a mask, and then growing a layer of dielectric (such as SiO) in the slit by a thin film growth process (such as PECVD)2) For connecting the driver and the micro lens;
step two: a dielectric film (e.g., SiO) is then grown on the substrate2Thin layer), growing a metal resistance layer (such as Pt) with a certain thickness (such as 100nm thickness) by using a thin film growth process (such as magnetron sputtering), forming a heating resistor of the driver by photoetching, and preparing a dielectric thin layer (such as SiO) on the metal resistance layer2) For insulation;
step three: on the basis of the steps, growing (such as sputtering) a layer of metal (such as aluminum), and then forming a reflecting mirror surface and an electrode on the driver and forming metal forming Bimorphh on the driver by adopting a stripping process;
step four: preparing a cross-shaped piezoresistor with a certain thickness (such as 2 mu m thickness) by using a film growth process, and etching to form a driver and a mirror structure;
step five: growing a dielectric layer (such as SiO) with a certain thickness (such as 2 μm thickness) on the back of the substrate2A thin layer), etching (for example, by using an RIE process) to etch a certain area, exposing Si, then etching a cavity with a certain depth (for example, 25 μm deep), then etching the dielectric layer in the middle area, and then etching the cavity until the buried oxide layer of the SOI silicon wafer is etched;
step six: the front side of the protective substrate is coated with photoresist (such as by spin coating), then the silicon dioxide of the buried oxide layer is etched to release the device (such as with hydrofluoric acid buffer), and then diced to obtain individual electrothermal micromirrors.
The above description is only for the preferred embodiment of the present invention, and all the physical dimensions or parameter values mentioned above are only for illustration and are not used to limit the protection scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The utility model provides an electric heat formula micro-mirror of integrated piezoresistive feedback which characterized in that: comprises a frame, a micro lens, a driver, a piezoresistor, a metal lead and a metal electrode; the driver comprises a conventional driver and an island structure driver;
the frame is a frame with a hollow middle part, the inner side of the frame horizontally extends out of an island-shaped structure, a piezoresistor with an angle sensing effect is formed on the surface of the island-shaped structure through diffusion or doping, the island-shaped structure is detected through the piezoresistor, the movement state change is generated under the drive of a driver, the deflection attitude of the micro mirror is detected in real time, the attitude information is fed back to a control center, and the deflection precision of the micro mirror is improved through the high-sensitivity piezoresistor feedback; the other end of the island-shaped structure is connected with a driver, and the driver is used for driving and supporting the micro lens; the micro lens is connected to the center of the frame through a connecting structure on the arm driver, so that the symmetrical layout and the extension in the length direction of the arm driver are facilitated; the metal lead and the metal electrode are arranged on the surface of the frame and used for applying loading voltage to the driver and the piezoresistors, the driver is heated to deform to drive the island-shaped structure to deform, the stress distribution of the driver is optimized, the piezoresistors are optimized to output, the temperature of a piezoresistor area is effectively reduced by isolating the piezoresistors in a thermal insulation mode when the voltage of the larger piezoresistors is output, the thermal noise of the piezoresistors is further suppressed, and the feedback control precision of the piezoresistors to the electric heating type micro-mirror is further improved.
2. The integrated piezoresistive feedback electrothermal micromirror of claim 1, wherein: the piezoresistive output is optimized by optimizing the stress distribution of the driver; the optimized driver comprises a spring connection mode and a direct connection mode according to the connection mode of the driver and the island-shaped structure;
the driver is in a spring connection type, the electrothermal micro mirror is in a spring connection structure, the left end and the right end of the driver are respectively connected with an insulating buffer area, the insulating buffer areas are connected with one end of a serpentine spring, the other end of the spring and an independent island-shaped structure form an elastic system, and a bridge type piezoresistor for detecting the motion state of the micro mirror after the micro mirror is heated is formed on the surface of the island-shaped structure through diffusion or doping;
adopt the lug connection formula to the driver, the electrothermal type micro mirror adopts direct connection formula connection structure, extend two cantilever beams respectively and pass through connection structure lug connection with the driver in the middle left side right-hand member on the frame, also be two cantilever beams symmetry in the left and right sides of island structure column structure, be favorable to the symmetric distribution of temperature like this, furthest's reduction temperature drift is to the influence that the pressure drag output brought, the cantilever beam form the bridge type pressure drag that is used for detecting the cantilever beam motion state after being heated through diffusion or doping on the surface, wherein pressure drag and pressure drag arrangement direction are perpendicular, are used for increasing the output of pressure drag.
3. The integrated piezoresistive feedback electrothermal micromirror of claim 2, wherein: in order to further facilitate the connection of the island-shaped structure and the driver, the frame is a rectangular frame with a hollow middle part, the inner side surface of the rectangular frame horizontally extends out of the island-shaped structure towards the center, so that the island-shaped structures are symmetrically distributed for facilitating current backflow, one part of the island-shaped structures are used for current inflow, and the other part of the island-shaped structures are used for current outflow; the free end of the island-shaped structure is laterally connected with the driver to play a role in supporting the driver.
4. The integrated piezoresistive feedback electrothermal micromirror of claim 2, wherein: the driver consists of six Bimorphh structures and a plurality of sections of silicon arms; the Bimorphh structure and the silicon arm are prepared on the basis of a monocrystalline silicon layer; the six-section bimorph has the same material composition except for the length, and the materials of the bimorph structure sequentially comprise Si, a lower layer insulating material, a heating resistor, an upper layer insulating material and metal from bottom to top, and deform when being heated; the silicon arm is made of Si, an insulating material, a heating resistor and an insulating material from bottom to top, wherein the heating resistor is a driver heating resistor; insulation between silicon and metal is realized through a Bimorph structure and a silicon arm layered layout, and the structural failure of Bimorph caused by the fact that metal ions are accumulated to one end of the metal in the Bimorph structure due to a charge accumulation effect is avoided; by optimizing the thickness ratio of the bimorph materials of the driver, the scanning range of the micromirror can be effectively enlarged on the basis of improving the deflection of the driver.
5. The integrated piezoresistive feedback electrothermal micromirror of claim 4, wherein: because the monocrystalline silicon can directly form the heater through doping, the dual functions of resistance heating and electric conduction are realized, and metal resistance is not needed, so that the electrothermal micro-mirror structure integrating piezoresistive feedback is simplified, and the cost is saved.
6. The integrated piezoresistive feedback electro-thermal micromirror of claim 5, wherein: the piezoresistive sensor is a high-temperature piezoresistive sensor, and in order to inhibit piezoresistive leakage current caused by temperature, an insulating groove is etched around the piezoresistive sensor during the preparation of the piezoresistive sensor, and then an insulating material is filled, so that heat insulation and leakage current inhibition are performed to the maximum extent, and the temperature range of the piezoresistive sensor is widened.
7. The integrated piezoresistive feedback electrothermal micromirror of claim 6, wherein: the structure of cantilever beam is the silicon film, and insulating material between piezoresistance and the silicon film for keep apart piezoresistance and silicon film, through keeping apart effectively reducing the regional temperature of piezoresistance to piezoresistance thermal insulation, and then restrain the thermal noise of piezoresistance, further improve the piezoresistance to electric heat formula micro mirror feedback control accuracy.
8. The integrated piezoresistive feedback electrothermal micromirror of claim 7, wherein: the metal electrode and the lead are Al, Ag, Au and Cu, and the metal resistor is Pt and W;
the insulating material is SiO2、PI、Si3N4；
The serpentine spring is made of Si, the insulating buffer area is made of silicon oxide, and the buffer area is connected with the cantilever beam structure through the serpentine spring structure.
9. An integrated piezoresistive feedback electro-thermal micro-mirror as claimed in claim 2, 3, 4, 5, 6, 7 or 8, wherein: for the spring connection mode, the manufacturing method comprises the following steps,
the method comprises the following steps: etching a slit with a certain depth On the front side of an SOI (Silicon-On-Insulator) substrate by using photoresist as a mask and adopting an etching process, and then growing a layer of insulating material in the slit by adopting a thin film process to connect a driver and a micro-lens;
step two: then growing an insulating thin layer on the substrate, then growing a layer of heating resistor with a certain thickness, peeling off the heating resistor to form a heating resistor of the driver, and preparing the insulating thin layer on the heating resistor for insulation;
step three: growing a layer of metal on the surface of the insulating thin layer, forming a reflecting surface on the mirror driver, forming electrodes around the frame structure, and forming each section of Bimorph on the driver;
step four: preparing a piezoresistor with a certain thickness, and etching to form a driver and a mirror structure;
step five: growing an insulating thin layer with a preset thickness on the back of the substrate, etching a certain area, exposing Si, etching a cavity with a certain depth, etching the insulating layer of the middle area, etching the cavity until the buried oxide layer is etched, and forming a step with a certain thickness in the middle area and the periphery of the middle area;
step six: and spin coating a protective layer on the front surface of the substrate for protection, then etching silicon dioxide of the oxygen burying layer to release the device, and then scribing to obtain a single electrothermal micro mirror.
10. An integrated piezoresistive feedback electrothermal micromirror as claimed in claim 2, 3, 4, 5, 6, 7 or 8, wherein: the method for fabricating the electrothermal micro-mirror comprises the following steps,
the method comprises the following steps: etching a slit with a certain depth On the front surface of an SOI (Silicon-On-Insulator) substrate by using photoresist as a mask and adopting an etching process, and then growing a layer of insulating material in the slit by adopting a thin film process for connecting a driver and a micro-lens;
step two: then growing an insulating thin layer on the substrate, then growing a layer of heating resistor with a certain thickness, peeling off the heating resistor to form a heating resistor of the driver, and preparing the insulating thin layer on the heating resistor for insulation;
step three: growing a layer of metal on the surface of the insulating thin layer, forming a reflecting surface on the mirror surface, forming electrodes around the frame structure, and forming each section of Bimorphh on the driver;
step four: preparing a piezoresistor with a certain thickness, and etching to form a driver and a mirror structure;
step five: growing an insulating thin layer with a preset thickness on the back of the substrate, etching a certain area, exposing Si, etching a cavity with a certain depth, etching the insulating layer of the middle area, etching the cavity until the buried oxide layer is etched, and forming a step with a certain thickness in the middle area and the periphery of the middle area;
step six: and spin coating a protective layer on the front surface of the substrate for protection, then etching silicon dioxide of the oxygen burying layer to release the device, and then scribing to obtain a single electrothermal micro mirror.
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| CN115629471A (en) * | 2022-10-10 | 2023-01-20 | 北京理工大学 | MEMS (micro-electromechanical system) electrothermal micro-mirror device with position detection structure and detection method |
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