TH72009B - Thin-film accelerometer sensors of floating mass and manufacturing processes. - Google Patents

Abstract

DC60 acceleration sensor is mainly fabricated using physical vapor deposition process. It consists of a floating mass in the center held together by a number of arms. This structure is protected by a silicone rubber sheet structure such as polydimethysiloxane (PDMS) that is fabricated by plastic molding and plasma bonding onto a glass substrate. The floating mass structure is then fabricated with a suitable insulating material such as Aluminum Nitride (AIN), Alumina (AI2O3), Silicon Nitride (Si3N4) or Silicon Dioxide (SiO2), followed by a thin film of piezoresistor coated on each arm and a thin film of a suitable metal such as Cu/Cr coated on the tip to serve as the electrodes. When the arms are bent by the force of acceleration applied, the piezoresistor bends and changes its electrical resistance. Therefore, the amount of acceleration applied is measured by measuring the change in electrical resistance of the device by the piezoresistor. In this invention, a suitable material such as indium tin oxide (ITO) is fabricated by a specific process, namely ion-assisted electron beam evaporation. The acceleration sensor fabricated primarily by physical vapor deposition process consists of a floating mass in the center held together by a plurality of arms. This structure is protected by a silicone rubber sheet structure such as polydimethysiloxane (PDMS) that is fabricated by plastic molding and plasma bonding onto a glass substrate. The floating mass structure is constructed of a suitable electrical insulating material such as Aluminum Nitride (AIN), Alumina (AI2O3), Silicon Nitride (Si3N4) or Silicon Dioxide (SiO2), followed by a thin film of piezoresistor coated on each of the arms and a thin film of a suitable metal such as Cu/Cr coated on the tip to serve as the electrodes. When the arms are bent by an accelerating force, the piezoresistor bends and changes its electrical resistance. Therefore, the amount of acceleration applied is measured by measuring the change in electrical resistance of the device by the piezoresistor. In this invention, a suitable material such as indium tin oxide (ITO) is fabricated by a specific process namely ion-assisted electron beam evaporation.

Claims (9)

All rights reserved which will not appear on the advertisement page:------01/03/2019------(OCR) Page 1 of 3 rights reserved pages. 1. An acceleration sensor device comprising: - a base plate (3) consisting of a first and second face, said base plate (3) being made of insulating material; - a floating mass (1) formed on a first face of said base plate (3) so that it is suspended above the surface with an air gap (7) beneath the arms, and at least one mounting arm (2) connecting said floating mass (1) to said base plate (3); - a plurality of thin films of piezoresistor (4) formed on each of said mounting arms (2), in a U-shaped coil pattern, wherein said thin films of piezoresistor (4) are made of a material having the property that its electrical resistance changes when a force is applied to it to cause a deformation; - a thin film compressive insulating layer (5) formed on the floating mass (1); - at least two electrodes (6) for connecting the thin films of - each of said piezoresistors (4) to serve as the output terminal of said acceleration sensor device, and - a protective structure (8) mounted on said base plate (3) and surrounding the floating mass structure and all others, wherein said acceleration sensor device has the characteristics of base plate (3) being an insulating material with a heat resistance of at least 250 °C, and has the characteristics of a thin film layer of piezoresistor (4) being indium tin oxide (ITO) material, and has the characteristics of said protective structure (8) being a silicone rubber sheet, and has the characteristics of a thin film compressed insulating layer (5) being formed on said floating mass (1) and over a portion of the thin film layer of piezoresistor (4) to increase the detection sensitivity of said sensor. 2. The acceleration sensor device according to claim 1, wherein the base plate (3) is made of glass or silica. 3. The acceleration sensor device according to claim 1, wherein the floating mass (1) is made of any one of Aluminum Nitride (AIN) or Alumina (Al2O3) or Silicon dioxide or Silicon Nitride. Page 2 of 3. 4. The acceleration sensor device according to any one of claims 1-3, wherein the floating mass (1) has a thickness between 1-4 micrometers. 5. The acceleration sensor device according to claim 1, wherein said piezoresistive material layer (4), namely Indium Tin Oxide (ITO), is coated on each arm. 6. The acceleration sensor device according to claim 1, wherein the thin film compression insulating layer (5) is made of either Aluminum Nitride (AIN) or Alumina (A120j) or Silicon dioxide or Silicon Nitride. 7. The acceleration sensor device according to claim 1, wherein the cover structure (8) is made of a polydimethysiloxane (PDMS) silicone rubber sheet material. 8. A process for manufacturing an acceleration sensor device, comprising: - providing a base plate (3) comprising a first and second surface; - providing a floating mass (1) made of electrical insulation and partly floating above a first surface of said base plate (3) and partly fixed to the first surface of said base plate by means of a fastening strip (2) at least at one point with a gap (7) in between; - providing a thin film of piezoresistor (4) on each arm (2) by ion-assisted electron beam evaporation; - providing a thin film of compressed insulating layer (5) coated on the floating mass (1) and the thin film of piezoresistor (4); - providing at least two terminals (6) for each piezoresistor (4) formed on the piezoresistor (4) to serve as the output terminals of said acceleration sensor device, and - providing a cover structure (8) surrounding the floating mass (1). The specific fabrication process of the aforementioned acceleration sensor device is as follows: - The fabrication of a photoresist layer (9) by photolithography into a rectangular or similar shape to support the aforementioned floating membrane (1); - The fabrication of the aforementioned floating mass (1) together with the mounting strips (2) to the required thickness by evaporation or sputtering. The evaporation or sputtering process for directly depositing an insulating material onto the photoresist layer (9) requires a special technique, namely, controlling the substrate temperature to be less than 90°C by controlling the coating time and energy, as well as water cooling at the substrate to prevent melting or etching of the photoresist layer (9); and - The removal of the aforementioned photoresist layer (9) to create a gap (7) between the aforementioned floating mass (1) and the aforementioned base layer (3). 9. The process for manufacturing an acceleration sensor device according to claim 8, wherein the step of forming said thin film insulating layer (5) is carried out by either an evaporation or a spattering process, and the step of forming at least two electrodes (6) of said thin film of piezoresistor (4) on said thin film of piezoresistor (5) with metal, carried out by either an evaporation or a sputering process.1 The process for manufacturing an acceleration sensor device according to claim 8, wherein the step of forming a cover structure (8) is made of a silicone rubber sheet such as polydimethysiloxane (PDMS) to be formed by plastic molding and plasma bonding onto a glass substrate, further comprising the steps of: - making a simple mold, starting with a temporary support plate (11), which may be a flat sheet of glass, metal, or silicone; then making a rectangular mold layer (12) of suitable thickness and size, which shall be larger than the entire floating mass structure; This rectangular layer (12) may be made from a suitable thick photoresist, e.g. - casting of PDMS liquid rubber onto a mold or hot embossing of PDMS solid rubber onto a mold - pulling the PDMS structure (8) out of the rectangular mold layer and - plasma bonding process to attach the PDMS structure (8) to the base plate (3), above and covering the entire floating mass structure. ------------ An acceleration sensor device comprising - a base plate (3) consisting of a first and second face, where said base plate (3) is made of insulating material - a floating mass (1) formed on one face of said base plate (3) to be suspended above the surface with an air gap (7) beneath the arms and at least one mounting arm (2) connecting said floating mass (1) to said base plate (3) - a thin film of - a plurality of piezoresistors (4) mounted on said mounting arms (2), each arm having a U-shaped coil pattern, wherein said piezoresistor (4) is made of a material having a characteristic property of its electrical resistance changing when a force is applied to it causing it to deform; - a thin film insulating layer (5) mounted on the floating mass (1) and over a portion of said piezoresistor (4) thin film; - at least two electrodes (6) for connecting each of said piezoresistor (4) thin film layers to serve as the output terminals of said acceleration sensing devices; and - a protective structure (8) mounted on a base plate (3) and surrounding the structure, floating mass, etc., wherein said acceleration sensing devices are characterized by a base plate (3) having the property of an insulating material capable of resisting heat of at least 250 °C, and a characteristic feature is the thin film layer of piezoresistors. (piezoresistor) (4) consisting of indium tin oxide (ITO) material and characterized by said protective structure (8) being a silicone rubber sheet and characterized by said thin film compressed insulating layer (5) formed on the floating mass (1) to increase the detection sensitivity of said sensor; the acceleration sensor device according to claim 1, wherein said base plate (3) is made of glass or silica; the acceleration sensor device according to claim 1, wherein said floating mass (1) is made of Aluminum Nitride (AIN), or Alumina(AI2O3), or Silicon dioxide, or Silicon Nitride; the acceleration sensor device according to claims 1-3, wherein said floating mass (1) has a thickness of 1-4 micrometers; the acceleration sensor device according to claim 1, wherein said layer of piezoresistive material (piezoresistive) said (4) is Indium Tin Oxide (ITO) coated on each of the mounting arms; the acceleration sensor device of claim 1, wherein said thin film compressed insulating layer (5) is made of either Aluminum Nitride (AIN), Alumina (Al2O3), Silicon dioxide, or Silicon Nitride; the acceleration sensor device of claim 1, wherein said protective structure (8) is made of polydimethysiloxane (PDMS) silicone rubber sheet material; the manufacturing process for the acceleration sensor device comprising: - providing a base plate (3) having one and two faces; - providing a floating mass (1) made of electrical insulation and partly floating above a first face of said base plate (3) and partly attached to a first face of said base plate by a stretch band (2) at least at one point with a gap (7) in between; - providing a thin film layer of piezoresistor (4) on each of said mounting arms (2). By ion-assistrd electron beam evaporation process - providing a thin film insulating layer (5) deposited on the floating mass (1) and the piezoresistor (4) thin film layer - providing at least two electrical steps (6) for each piezoresistor (4) thin film layer formed on the piezoresistor (4) to act as the output terminals of said acceleration sensor device and - providing a protective structure (8) surrounding the said floating mass (1), wherein the manufacturing process of said acceleration sensor device is characterized in that the step of providing the said floating mass (1) comprises the steps of - forming a photoresist layer (9) by photolithography process. (photolithography) is a rectangular or similar shape for supporting said floating membrane (1); - fabricating said floating mass (1) together with a retaining strip (2) of desired thickness by evaporation or sputtering process. By evaporation or sputtering process for directly depositing an electrically insulating material onto a layer of photoresist (9), special techniques shall be used, namely, controlling the substrate temperature below 90°C by controlling the time and energy of the deposition, including water cooling at the substrate to prevent melting or etching of the photoresist layer (9); and - removing said photoresist layer (9) so as to create said gap (7) between said floating mass (1) and said base layer (3). The process for manufacturing an acceleration sensor device according to claim 8, wherein the step of depositing said thin film compressed insulating layer (5) is performed by either evaporation or sputtering process, and the step of depositing at least two electrically insulating layers (6) on the thin film of piezoresistor (4). 1. The process for fabricating the acceleration sensor device according to claim 8, wherein the protective structure (8) is made of a silicone rubber sheet such as polydimethysiloxane (PDMS) to be formed by plastic molding and plasma bonding onto a glass substrate, further comprising the steps of: - fabricating a simple mold, starting with a temporary base plate (11), which may be a flat sheet of glass, metal, or silicon; then fabricating a rectangular mold layer (12) of suitable thickness and size, which shall be larger than the entire floating mass structure; These 12 square layers may be made from a suitable thick photoresist such as SU8 - casting of PDMS liquid rubber onto a mold or hot embossing of PDMS solid rubber onto a mold - pulling the PDMS structure (8) out of the square mold layer and - plasma bonding to attach the PDMS structure (8) to the substrate (3) above and covering the entire floating mass structure.