mems accelerometer designing and fabrication
DESCRIPTION
Design,fabrication and Application of MEMS accelerometer.TRANSCRIPT
![Page 1: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/1.jpg)
Presented by:-
PRASHANT SINGH
MEMS CAPACITIVE
ACCELEROMETER (Design and Fabrication)
![Page 2: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/2.jpg)
OUTLINE Introduction
MEMS MEMS vs. IC’s
Accelerometer Basic operation principle Capacitive Accelerometer
Capacitance basics Sensing mechanism Structure analysis (spring stiffness) Advantages
Accelerometer fabrication Applications
![Page 3: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/3.jpg)
INTRODUCTION MEMS
Micro-Electro-mechanical-system Integration of mechanical unit, electrical unit, sensor and actuator on a
single substrate. MEMS:
MEMS move and Sense Mass. MEMS act as transducer (Sensor & Actuator).
IC IC’s move & sense electrons. IC’s acts as sensor not actuator.
MEMS Advantage Smaller Lighter Economical
![Page 4: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/4.jpg)
ACCELEROMETER Inertial sensor:
Newton’s 1st law (Mass of inertia). Device used to measure:
Acceleration Displacement Force Inclination
Design Approach: Piezoelectric Piezoresistive Tunneling Capacitive, etc.
Basic capacitive Accelerometer.
![Page 5: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/5.jpg)
BASIC OPERATION PRINCIPLE Newton’s 1st law (Mass of inertia). Newton’s 2nd law: F=ma. Accelerometer model: 2nd order spring-damper
model. Force ‘Fe’ applied on the frame. Reference frame displacement- Xf Proof mass displacement- Xm
{}
![Page 6: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/6.jpg)
CAPACITIVE ACCELEROMETER Based on Change in capacitance between Comb
fingers. {Capacitance change} α {Force applied on Proof
Mass} Comb structure Large capacitance value Advantages
High resolution Good DC response Linear output low power dissipation Easy incorporation with CMOS
![Page 7: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/7.jpg)
CAPACITANCE BASICS
A= overlapping area
d= separation between fingers
C change depends on ‘l’, ‘w’ & ‘d’.
Capacitance change
, ,
![Page 8: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/8.jpg)
SENSING MECHANISM
Two types: Out-of-Plane Sensing
Change in overlapping width (w). In-Plane sensing
Lateral sensing (a) Change in overlapping length (L)
Transverse sensing (b) Change in finger gap (d)
(a)
(b)
![Page 9: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/9.jpg)
STRUCTURE ANALYSIS Three elements:
Proof mass Comb structure Proof mass support (beam or spring)
Spring stiffness (k) Also defined for beam.
K
Unguided and guided beam structure
![Page 10: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/10.jpg)
CAPACITIVE ACCELEROMETER ADVANTAGES
High sensitivity. Easy readout circuitry. Independent of temperature variation. Easy fabrication (two level mask). Large noise margin. Fabrication on silicon. Compatible with CMOS technology.
![Page 11: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/11.jpg)
FABRICATION PROCESS
silicon
oxidesilicon
oxidesiliconoxide
Silicon on insulator(SOI) wafer(i) Cleaning -RCA 1
-RCA 2
Oxidation(ii) thickness of oxide layer ::7700 Å at 1050ºC
Photolithography(iii)-1st level mask
-prebaking
-UV light exposer-15 sec
-PR develop
silicon
475µm
2µm15µm
silicon
oxideSilicon
photoresist
(i)
(ii)
(iii)
oxide
oxide
![Page 12: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/12.jpg)
FABRICATION PROCESS CONTD..
SiO2 etch (iv)
–buffer HF
-etch rate ≈ 1000Å/min.
Silicon etch(v)-PR removal
-Anisotropic Si etch
-THAH solution used
-V groove formation
silicon
oxideSilicon
oxide
oxide
silicon
oxide
oxide
(iv)
(v)
![Page 13: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/13.jpg)
FABRICATION PROCESS CONTD..
SiO2 removal (vi)-Buffer HF
-hanging structure
Metallization (vii)-2nd level mask
-Al deposited
-temp. 650ºC
silicon
oxide
(vi)
silicon
oxide
(vii)
![Page 14: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/14.jpg)
ACCELEROMETER FABRICATION CONTD..
Accelerometer (1st level mask, PR developed)
Accelerometer (SiO2 etched)
SiO2
Si
SiO2
Si
photoresist
![Page 15: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/15.jpg)
APPLICATIONS
Automotive Crash detection & Air bag deployment.
Consumer Electronics hard disk protection(laptops) screen rotation (mobile) Image stabilization (camera)
Industrial Vibration detection (machine) crack detection (pulley)
Aerospace & Defence Navigation Missile guidance Thrust detection Accelerometer application
![Page 16: Mems accelerometer designing and fabrication](https://reader036.vdocuments.net/reader036/viewer/2022081715/547f59aeb4af9f94728b47b5/html5/thumbnails/16.jpg)
THANK YOU