NW-NEMFET: Steep Subthreshold Nanowire Nanoelectromechanical Field-Effect Transistor

Transcription

1 NW-NEMFET: Steep Subthreshold Nanowire Nanoelectromechanical Field-Effect Transistor Jie Xiang Electrical and Computer Engineering and Materials Science Engineering University of California, San Diego Energy Efficient Electronic Systems Symposium, Oct. 29, 2013, Berkeley

2 Acknowledgements Xiang Lab Ji-Hun Kim Zack C.Y. Chen SoonShin Kwon Han-Ping Chen Former Members Peida Zhao Kyle F. Garton Dr. Mingliang Zhang Collaborators Prof. Renkun Chen Prof. Baowen Li Prof. Yuan Taur Prof. Peter Asbeck Prof. Jennifer Cha Prof. Deli Wang Matt Wingert Facility CalIT 2 Nano3 facility UCSD Cryo-Electron Microscopy Facility with support by NIH and Agouron Institute Electrical, Communications and Cyber Systems (ECCS) Startup Fund Senate Research Award Hellman Fellow

3 MOSFET Static Power Exponentially Dependent on S.S. P = ACV 2 f + VI leak Dynamic 60 mv/ dec I I I I I leak G GIDL off off qvth exp( ) kt d B Vg kt B SS ln10 log I q P V I static DD off Static Vth exp( ) SS

4 Output I MOSFET S.S. are thermally limited by nonscaling factor k B T I on V threshold PMOS V dd I off I on Input V g 0 S.S. A ideal switch I off

5 Output I MOSFET S.S. are thermally limited by nonscaling factor k B T I on V threshold PMOS V dd I off gate I on Input V g Abrupt electromechanical pull-in does not depend on k B T Similar source-drain current as MOS when on 0 S.S. A ideal switch I off

6 Early Proposed NEMFET/Suspended Gate FET Wong, Philip et al, IEEE Trans. on Electron Devices (2008) Tsu-Jae, King et.al. IEDM (2005)

7 Limitations of experimental suspended-gate FET Large gate mass limits resonant frequency to ~16 MHz High voltage and large onoff V g window ~ 5 V How does it scale towards NEMS? N. Abele et al, IEDM (2005) ; IEDM (2006)

8 What is Nanoelectromechanical Systems (NEMS)? 1 mm

9 Nanowire Nanoelectromechanical Systems (NEMS) with GHz resonance Fast f 0 ~ GHz Sensitive transducers Mass sensitivity: yocto~zepto gram Force sensitivity ~ pn Huang XMH, et.al., Nature (Caltech)

10 NEMFET is not the following 2 / 3 Terminal NEM contact switches S. W. Lee, et al., Nano Letters, J. E. Jang, et al., Appl. Phys. Lett., X.L.Feng, et al., Nano. Lett., Lee, J. O. et al. Nat Nano 8, 36-40, (2013). NEMFET does not require metal-metal or metal-semiconductor contact Potential to alleviate reliability concerns

11 NW NEMFET : Basic Device Design and Simulation Zero V G Drain Nanowire Gate oxide Gate Source Accumulation Increase V G Mechanical force Si Ge Electro-static force Pull-In Occurs Depleted

12 Modeling NEMFET device characteristics V DD window on-off ratio within a 0.5V V DD window High I ON /I OFF ratio within 1V DD compared to 4V DD Higher p-doping of the NW leads to high off-current for the stuckstate JH. Kim, C. Chen, DRC (2013)

13 Gen 1 NEMFET: a contact switch Process Flow JH. Kim DRC (2013)

14 Gen 2 NEMFET: back gated V PULL-IN NW diameter : 28nnm L CH : 1.68um t GAP 80nm Gate oxide 40nm ZrO 2 V GS Sweep Direction V PULL-OUT V PI : 10.8V V PO : 6.5V I ON /I OFF : 10.7 S.S. : <15mV 1um JH. Kim DRC (2013)

15 Final NEMFET with HfO 2 dielectrics L: 1.3 mm 100 mm x gap : 35 nm D: nm 5 mm Atomic level control of air gap reduction by ALD coating

16 Near Zero S.S. at Room Temperature V pi -V po = 1.6 V 12 mv/dec V d = 1 V V pi : 14.48V S.S. : 6 mv/dec (limited by bin size) I on /I off : 2200 (limited by stuck-state off current) I on = 2 ma

17 Stable, multiple switching with < 1V voltage window Initial rise but stabilized operational voltage window (V pi -V po ) = 0.83±0.52 V Eventually failed due to stiction. JH. Kim (submitted)

18 NEMFET resonance at 126 MHz (VHF) I MIX measurement with 400Hz/99% AM modulation Measured f 0 = 126MHz; Q = 630 at 40 mv drive. Quadratic dependency of f 0 to AC drive voltage

19 Gate and bias dependence of resonance frequency elucidates how nanowire is tensioned and driven f o vs. V g Elastic Hardening. Nanowire has no slack f o vs. V d Capacitive Softening (Effective side gate effect) V ac V g dc GND V.A. Sazonova Cornell thesis (2006) JH. Kim (submitted)

20 Device Speed and Scaling a design window for Si-based NW NEMFET Airgap fixed at 10 nm. >300 MHz with 5 V V pull-in can be achieved using SiNWs with 11.7 nm diameter. Readily available in our laboratory. Sub 1V operation for diameter smaller than 5 nm. More aggressive scaling with CNT, graphene and other 2D monolayer materials

21 Conclusion Low-Power, High-Speed NEMFET ~ 0 mv/dec S.S. circumvents thermodynamic limit to sharp switching VHF operation with small voltage window requirements (< 1 V) due to nanowire beam structure Can enable both logic and non-volatile memory Next steps: Improvements needed on doping and surface states control in Si/Ge based channels. Further scaling and interface fixed charge planting for reduced V pi. Explore new carbon-based or molecular monolayer materials.