MEMS technology is one of the advanced technologies used by many manufacturers. In the first two articles, Xiaobian introduced the request scheduling algorithm and fault management of MEMS storage devices. In order to enhance our understanding of MEMS, this paper will elaborate the typical MEMS process and the application prospect of MEMS accelerometer. If you are interested in MEMS, read on.
1、 Typical process flow of MEMS
MEMS surface micromachining process refers to the MEMS manufacturing process in which all processes are carried out on the wafer surface. In surface micromachining, low pressure chemical vapor deposition (LPCVD) is used to obtain thin films as structural units. The surface micromachining process uses a number of deposition layers to fabricate the structure, and then releases the components, allowing them to move horizontally and longitudinally to form MEMS actuators. The most common surface micromechanical structure material is polycrystalline silicon deposited by lpvcd. The properties of polycrystalline silicon are stable and isotropic. By carefully controlling the deposition process, the film stress can be well controlled. In addition, the surface micromachining process is compatible with the IC production process and has a high degree of integration.
Next, combined with the MEMS standard process of Peking University Institute of Microsystems, taking the beam, the most important structure in MEMS, as an example to introduce the specific process of MEMS surface processing.
1. Silicon preparation
2. Silica (SiO2) was grown as insulating layer
3. Silicon nitride (Si3N4) was deposited by LPCVD as insulation and anti-corrosion layer
4. Polycrystalline silicon 1 (poly1) was deposited by LPCVD as the bottom electrode
5. Polysilicon doping and annealing
6. Lithography and etching of poly1, pattern transfer to get poly1 pattern
7. LPCVD PSG as sacrificial layer
8. Lithography and etch PSG, transfer the pattern to get bump pattern
9. Lithography and etching PSG to form anchor region
10. Polycrystalline silicon 2 (poly2) was deposited by LPCVD as structure layer
11. Polysilicon doping and annealing
12. Lithography and etching of poly2, pattern transfer to get poly2 structure layer pattern
13. Sputtered aluminum (AL) layer
14. Lithography and etching of aluminum layer, pattern transfer to get metal layer pattern
15. Release the structure of the activity
So far, we have completed the fabrication of a beam using MEMS surface processing technology. There are five masks in this process
1. Poly1, with positive plate, the polycrystalline 1 pattern is used to provide electrical connection of mechanical layer, ground plate or shielding electrode;
2. Bump, using a negative plate, forms a groove on the sacrificial layer, which makes a small protrusion on the polysilicon mechanical layer formed later, reduces the contact area between the mechanical layer and the substrate during the release process or working process, and has a certain anti adhesion effect;
3. Anchor, using a negative plate, carves holes on the sacrificial layer to form the prop of the mechanical layer on the substrate and provides electrical connection;
4. Poly2, using positive plate, is used to form polysilicon mechanical structure;
5. Metal, with a positive plate, is used to form electrical connection or test contact.
2、 Application prospect of MEMS accelerometer
MEMS sensors, namely micro electromechanical systems (MEMS), are interdisciplinary frontier research fields developed on the basis of microelectronics technology. After more than 40 years of development, it has become one of the major scientific and technological fields attracting worldwide attention. It involves electronics, machinery, materials, physics, chemistry, biology, medicine and other disciplines and technologies, and has broad application prospects. MEMS accelerometer is one of them.
At present, three axis MEMS accelerometers are used to develop new applications: mobile phones with motion detection and state perception to monitor the location and usage of mobile phones. The sensor can provide many functions, such as more intuitive user interface and intelligent power management to extend battery life. Notebook computer and media player with hard disk protection system. With the increase of storage capacity requirements for portable devices, measuring impact and drop events helps to improve the robustness of products.
Mobile game machine provides more interactive, intuitive and interesting game experience by improving the interface of current games and developing new sports based games. Digital camera can automatically help users take better photos by detecting position, motion and vibration. Because these new functions can make the product more distinctive, the 3-axis MEMS accelerometer is also recognized by portable device manufacturers. After the price is reduced to an acceptable level, 3-axis MEMS accelerometers will be widely used in mobile phones, media players, video game machines, cameras, computers and other products, with huge market potential