High-Speed Devices, 2011 Erik Lind (Erik.Lind@ftf.lth.se) Course consists of: 30 h Lectures (H322, and Fys B check schedule) 8h Excercises 2x2h+4h Lab Excercises (2 Computer simulations, 4 RF measurment lab) Written report on device performance (2-3 pages), w/ 10 min oral presentation Written Exam (15/12) Course Material Fundamentals of III-V Devices, William Liu ppt-slides from lectures Course Homepage - http://wwwgu.ftf.lth.se/courses/fff115.html Download and bring slides to the lectures!! 1
My Background M.Sc. in Engineering Physics (2000) Ph.D. in Solid State Physics 2004 Post Doc at UC Santa Barbara, 2006-2007 Assistant Professor (Forskarassistent) @ Solid State Physics 2007- Ph.D.: Tunneling devices, (Quantum dots, SiGe Esaki tunnel diodes, and Resonant Tunneling diodes/transistors) Post Doc: High-speed InP/InGaAs DHBTs (500+ GHz f t, f max ) Currently: InAs nanowire transistors, UWB sources, III-V MOSFETs 2
Locations My office: C367 EIT k-space 2011-01-13 3 Introduction, High Speed Devices 2011
Course Contents Review of basic semiconductor physics (no real derivations), Carrier statistics, Transport & Continuity Equations, Electrostatics (2) Heterojunctions, especially pn-heterojunctions (2) Heterobipolar transistors (HBTs) DC and AC operation (4) Heterostructure Field Effect Transistors (HFET, HEMT) DC and AC operation (3) Device Scaling Laws (HBTs and HFETs) (1) Ballistic FETs (1) Resonant Tunneling Diodes (1) 4
Course Goals Device Physics : Heterojunctions Heterojunction Bipolar Transistor Field Effect Transistors Semiconductor Physics: Electrostatics Electron Transport Eqs. Electron Dynamic Eqs. High Freuency Behaviour: Functionallity Design Scaling laws Material Science: Bandgaps, Heterojunctions, Mobilities 5
Project Illustrate state-of-the-art device performance Litterature Study on different type of devices Present your finding to the other students, 10 min or so. 6
Laborations 2 Computer labs: Simulate HBT and FET using TCAD program (2x2 h). 1 Device analysis lab. Measure high frequency parameters, extract certain device parameters. Lab report, gives bonus points on exam (1x4 h). 7
Heterostructure Bipolar Transistor (HBT) InP Emitter (n + ) InGaAs Base (p ++ ) InP Collector (n) Similar to ordinary BJT Uses large bandgap emitter Very high base-doping > Low base resistance! pn junctions Diffusion Across the base Quasi Fermi Levels Drift in the collector E c E c E c E v E v 8
Heterostructure Field Effect Transistor / High Electron Mobility Transistor (HFET/HEMT) Source V gs V ds Wide bandgap w/ doping Wide bandgap w/o doping Narrow Bandgap channel w/o doping x Gate Contact Wide Bandgap Small bandgap channel High mobility! Similar to ordinary MOSFET Utilizes a large bandgap as isolation Moves mobile channel charge away from oxide interface & any doping Very high mobility!! E f Drift current, velocity saturation and ballistic transport 9
Physical realization HBT HFET 62.5 nm Who to connect between: Material science Semiconductor Physics Models for circuit design! 10
2 minute exercise - linearization df ( x) f ( x x) f ( x) ( x) x dx i ds =f(v ds ) v ds v i g d V I i v v i 11
Important device metrics I ds =f(v gs,v ds ) V ds V gs Small signal analysis: v V v, i I i i f ( v, v GS ) f ( V, V GS f ) v GS V v GS f v V GS v Transconductance: g m g d :Output conductance 12
Voltage Gain (db) High speed design: Common-source amplifier V ds R L 15 3dB point v o 10 v i + - 5 0-5 10 6 10 7 10 8 10 9 10 10 10 11 Frequency (Hz) Voltage gain: A v f v v o i g m R L, eq 1 jr g C gs 1 1 g m R L, eq C gd DC-gain High gain, large 3dB roll off point: Large g m, small g d, small C s! Meyer, Gray: Chapter 7 13