20 MHz Free-Free Beam Microelectromechanical Filter with High Quality Factor

Transcription

1 20 MHz Free-Free Beam Microelectromechanical Filter with High Quality Factor Group 4 Yang Lu 1, Tianfeng Lu 1, Han Wang 2, Zichen Tang 2 1 Department of Material Science and Engineering 2 Department of Electrical and System Engineering 04/21/2015

2 Outline Introduction Design and Performance Fabrication Discussion

3 Outline Introduction Design and Performance Fabrication Discussion

4 Introduction Electronic Filter Remove unwanted frequency component Enhance wanted frequency component Low Pass High Pass Band Pass 1

5 Introduction Electronic Filter Resonance frequency f 0 : circuit impedance at minimum f LC Quality factor Q Stored energy to dissipated energy inversely proportional to band width Q L 1 CR 2

6 Introduction MEMS Filter Why MEMS? It is small. Less materials lower cost Faster higher f 0 (f ~ [s] -1 ) Gentleness smaller force lower power higher Q Not only the size! Integration with CMOS circuits on one chip Compatible with circuit design Piezoelectric: thickness MEMS: literal dimensions 3

7 Introduction MEMS Filter Why free-free beam? f Simple [ ] 2 L 0 2 EI Less (anchor) dissipation Clamped-clamped beam Larger stiffness at the cost of increased anchor dissipation (Q decreases with higher f 0 ) 4

8 Outline Introduction Design and Performance Fabrication Discussion

9 Design Schematic View Anchor Torsional Support Electrode (bottom capacitor pad) Beam Electrode (connected to beam) Doped poly-si Si 3 N 4 Substrate 5

10 Design Design Parameters Anchor Torsional Support Electrode (bottom capacitor pad) L 0 L Beam t Electrode (connected to beam V 0 H W Si 3 N 4 Substrate 6

11 Design Design Parameters 1. Resonance frequency f 1 k EI H E [ ] 20MHz 2 m 2 L 2 L H = 2 μm, L = 28.7 μm To determine W m WHL 0 k EI EWH 3 3 L L (1 0.6 / ) 1.239(1 0.6 / ) 2 W = 5 μm W L W L W L WL ( ) H 3 3 t mk t E 7 0 2

12 Design Design Parameters 2. Equivalent Circuit EWH k N / m 3 L 13 m WHL kg

13 Design Design Parameters 2. Equivalent Circuit R m km Q z = 1.239(1-0.6W / L)m ( WL 1 t 3 Er H )2 Q 2 0 C V t WL V t Small t is preferred to get small R m 9

14 Design Design Parameters 2. Equivalent Circuit v() t v e m jwt i v fc i ac m 2 mot R 0 C 0 v m WL t (2 fl ) 2 2 m m 2 fcm Ideally, i ac <<i mot Small C 0, i.e. small L 0 is preferred Large V 0 is needed 10

15 Design Design Parameters 2. Equivalent Circuit t = 100 nm Pa s 5 Q R m km Q / C m V 0 = 80 V V / 0WL0 2 V t 0 L 0 = 10 μm V pull in 3 8kt 27 WL o 0 84V 8 E V m t 11

16 Design Design Parameters 2. Equivalent Circuit R m km Q Cm k m F Lm H Q L C m m 1 R m

17 Performance Simulated I vs. f 10-3 v m = 1 V i mot 10-3 v m = 1 V f 0 = MHz i (A) i ac i tot (A) BW < 1 khz M 20.0M 20.1M 20.2M M 20.0M 20.1M 20.2M f (Hz) f (Hz) 13

18 Outline Introduction Design and Performance Fabrication Discussion

19 Fabrication 1. Deposit isolation layer 2. Deposit polysilicon and dope with boron LPCVD Si 3 N 4 LPCVD Polysilicon 3. Pattern the poly and plasma etch 4. Deposit sacrificial oxide (100nm) Pattern anchor openings and RIE Sacrificial SiO 2 Anchor opening 14

20 Fabrication 5. Deposit structural polysilicon, dope with boron again and pattern the beam Photoresist Structural Poly 6. Plasma etching to form the beam 7. Release structure by HF etching of sacrificial oxide and then deposit Al electrode Al Al 15

21 Outline Introduction Design and Performance Fabrication Discussion

22 Discussion 1. Enhance Fabrication Accuracy Problem: Thin sacrificial layer Uniformity issues Hard to etch (remaining byproducts) Solution: Dimple support Advantage: Thicker oxide Better quality Easier to etching 16

23 Discussion 2. Achieve R m =1000Ω Shrink the size R m ~ [s] 1 Difficult to fabricate Increase quality factor Q = km h 2 R m Introduce vacuum packaging to reduce the damping of the device. 17

24 Discussion 3. Vacuum Packaging ~ 33 torr base pressure is achieved J. Chae et al. Fabrication and Characterization of a Wafer-Level MEMS Vacuum Package With Vertical Feedthroughs. Journal Of Microelectromechanical Systems, Vol. 17, No. 1, February

25 Discussion 4. Further increase of f 0 Shrink the size to nanometer? scaling-induced limitations (impedance mismatch, power handling) Use higher order oscillation modes Position of the torsional supports (node points) Other structures rather than beams Contour-mode disks (Q 1.5 GHz) 19

26 References 1. RLC Circuit in wikipedia 2. Nguyen, CT-C. Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on 54.2 (2007): Bannon, Frank Diii, John R. Clark, and CT-C. Nguyen. Solid-State Circuits, IEEE Journal of 35.4 (2000): Li, S. S., et al. Proceedings, 17th Int. IEEE Micro Electro Mechanical Systems Conf Wang, Kun, Ark-Chew Wong, and CT-C. Nguyen. Microelectromechanical Systems, Journal of 9.3 (2000): Demirci, Mustafa U., and CT-C. Nguyen. Frequency Control Symposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, Proceedings of the 2003 IEEE International. IEEE, Junseok Chae, Joseph M. Giachino and Khalil Najafi. Fabrication and Characterization of a Wafer-Level MEMS Vacuum Package With Vertical Feedthroughs. Journal Of Microelectromechanical Systems, Vol. 17, No. 1, February

27 Q&A Thank you!