MEMS: Microelectromechanical Systems

Transcription

1 MEMS: Microelectromechaical Systems What are MEMS? Micro-electro-mechaical systems miiaturized mechaical ad electro-mechaical elemets havig some sort of mechaical fuctioality Covert betwee measured mechaical sigals ad electrical sigals CSE/EE

2 Fudametals of MEMS Devices Silico q Already i use q Maipulatable coductivity q Allows for itegratio Thi-Film Materials q Silico dioxide q Silico itride CSE/EE Micromachiig Fabricatio Thi Films q Layers (µm) put o Si q Photomask Positive or egative Wet Etchig q Isotropic q Aisotropic q KOH CSE/EE

3 Micromachiig Fabricatio II Dry Etchig q RIE q DRIE Rate-Modified Etchig q Cover with Boro q Wet etch with KOH CSE/EE Surface Micromachiig Grow silico dioxide Apply photoresist Expose ad develop Etch silico dioxide Remove photoresist Deposit polysilico Remove silico dioxide CSE/EE

4 MEMS Packagig Purposes q Reduce EMI q Dissipate Heat q Miimize CTE q Deliver Required Power q Survive Eviromet CSE/EE Types of MEMS Packages Ceramic Packagig q Hermetic whe sealed q High Youg s Modulus q Flip Chip or Wirebodig Plastic Packagig q Not Hermetic q Postmoldig q Premoldig Metal Packagig q Hermetic whe sealed q Easy to assemble q Low Pi Cout CSE/EE

5 Typical MEMS Devices Sesors q Pressure Sesors q Accelerometers Actuators q Gyroscopes q High Aspect Ratio Electrostatic Resoators q Thermal Actuators q Magetic Actuators q Comb-drives CSE/EE Typical MEMS Devices Sesors q Pressure Sesors q Accelerometers Actuators q Gyroscopes q High Aspect Ratio Electrostatic Resoators q Thermal Actuators q Magetic Actuators q Comb-drives CSE/EE

6 Accelerometers Applicatios: q Air bag crash sesors q Active suspesio systems q Atilock brake systems q Ride cotrol systems q Smartphoes Uits of mv/g CSE/EE MEMS Accelerometer Mass, Sprig, Damper Model CSE/EE

7 MEMS Accelerometer CSE/EE MEMS Accelerometer (cot d) CSE/EE

8 Accelerometer Priciple mass-sprig type accelerometer q To icrease accelerometer sesitivity : m large or K small CSE/EE Accelerometer Priciple Aalog Devices ADXL202 q surface-micromachied accelerometer Sesor Priciple measure capacitace, which is iversely proportioal to the gap q To icrease accelerometer sesitivity : large m, small K, large A CSE/EE

9 ADXL 202 Dual Axis Accelerometers To icrease the mass, commo beam mass is used x directio acceleratio is detected here y x sprig CSE/EE MEMS Gyroscopes Typically Vibratory Gyroscopes q Utilize Coriolis Acceleratio ( fictioal force ) q Due to rotatig referece frame CSE/EE

10 Coriolis force CSE/EE Coriolis force CSE/EE

11 Types of Vibratory Gyroscopes Vibratig Beam, Vibratig Disk, Vibratig Shell CSE/EE Gyroscope Gyroscopic Precessio q What will happe if there is rotatio aroud the rotatio axis CSE/EE

12 Coriolis Acceleratio Coriolis acceleratio q A perso movig orthward toward the outer edge of a rotatig platform must icrease the westward speed compoet (blue arrows) to maitai a orthboud course. The acceleratio required is the Coriolis acceleratio. CSE/EE Coriolis Acceleratio Costraied motio meas force is applied turig fork gyroscope CSE/EE

13 Gyroscope usig Coriolis effect Schematic of the gyro s mechaical structure The displacemet is proportioal to the rotatio speed CSE/EE Disc Resoatig Gyro Basics CSE/EE

14 Disc Resoatig Gyro Basics Gyroscope is drive to resoate i-plae Electrodes sese deflectio i outer rig sockets Electrodes actuate i ier rig sockets Circuits process the sigal ad feedback ito the system CSE/EE Operatio Priciple of the DRG CSE/EE

15 Coriolis Effect Coriolis acceleratio (a) occurs if a resoatig disc is pterturbed Depeds o velocities o the disc è higher frequecies allow Coriolis acceleratio to domiate cetrifugal acceleratio Coriolis acceleratio is what the electrodes sese through chage i capacitace CSE/EE How Does the DRG Work? DC Source creates a electrostatic force that moves the disc Proper cotrol of these electrodes ca put the system ito resoace Similarly, the sesig electrodes use gap chages to gauge system chages CSE/EE

16 Oe Rig or May? Oe major advatage of this system is its large area Compared to a sigle rig gyro, has much more cotrol over actuatio ad sesig Sigle rigs require flexible support beams as well CSE/EE Why Cut the Circles? With full cocetric circles, the structure teds to be rigid By usig arcs istead, the structure becomes more flexible, allowig for better accuracy ad performace CSE/EE

17 CSE/EE Ivesese MPU axis gyroscope ad accelerometer 4 x 4 x 1 mm CSE/EE

18 MPU-6050 Supply voltage of 2.375V 3.46V Curret of 3.9mA Uses a I2C bus Selectable gyroscope ad accelerometer rages 1MHz iteral clock CSE/EE CSE/EE

19 Sample MPU-6050 data The accelerometer ad gyroscope measuremets are explaied i the MPU-6050 datasheet i the GYRO_CONFIG ad ACCEL_CONFIG register descriptios (sectios 4.4 ad 4.5 o pages 14 ad 15). The scale of each depeds o the sesitivity settigs chose q q +/- 2, 4, 8, or 16g for the accelerometer +/- 250, 500, 1000, or 2000 deg/sec for the gyroscope. The accelerometer produces data i uits of acceleratio (distace over time2) The gyroscope produces data i uits of rotatioal velocity (rotatio distace over time). CSE/EE Sample MPU-6050 data The output scale for ay settig is [-32768, ] for each of the six axes. The default settig i our example is +/- 2g for the accel ad +/- 250 deg/sec for the gyro. If the device is perfectly level ad ot movig, the: q X/Y accel axes should read 0 q Z accel axis should read 1g, which is at a sesitivity of 2g q X/Y/Z gyro axes should read 0 I reality, the accel axes wo't read exactly 0 sice it is difficult to be perfectly level ad there is some oise/error, ad the gyros will also ot read exactly 0 for the same reaso (oise/error). CSE/EE

20 Sample MPU-6050 data MPU6050 is olie... x-axis self test: acceleratio trim withi : 0.6% of factory value y-axis self test: acceleratio trim withi : 0.6% of factory value z-axis self test: acceleratio trim withi : 0.7% of factory value x-axis self test: gyratio trim withi : 0.2% of factory value y-axis self test: gyratio trim withi : -0.2% of factory value z-axis self test: gyratio trim withi : 0.3% of factory value MPU6050 iitialized for active data mode... X-acceleratio: mg Y-acceleratio: 1.71 mg Z-acceleratio: mg X-gyro rate: -1.9 degrees/sec Y-gyro rate: 0.3 degrees/sec Z-gyro rate: -0.3 degrees/sec Temperature is degrees C X-acceleratio: mg Y-acceleratio: 0.98 mg Z-acceleratio: mg X-gyro rate: 0.4 degrees/sec Y-gyro rate: 0.1 degrees/sec Z-gyro rate: 0.0 degrees/sec Temperature is degrees C CSE/EE CSE/EE