Vibhor Jain , Evan Lobisser, Ashish Baraskar, Brian J Thibeault, Mark Rodwell

1. InP and Related Materials 2011 InGaAs/InP DHBTs demonstrating simultaneous ft/fmax ~ 460/850 GHz in a refractory emitter process Vibhor Jain, Evan Lobisser, Ashish Baraskar, Brian J Thibeault, Mark Rodwell ECE Department, University of California, Santa Barbara, CA 93106-9560 Miguel Urteaga Teledyne Scientific & Imaging, Thousand Oaks, CA 91360 D Loubychev, A Snyder, Y Wu, J M Fastenau, W K Liu IQE Inc., 119 Technology Drive, Bethlehem, PA 18015 vibhor@ece.ucsb.edu, 805-893-3273

2. Outline • Need for high speed HBTs • HBT Scaling Laws • Fabrication • Challenges • Process Development • DHBT • Epitaxial Design • Results • Summary

3. Digital Logic for Optical fiber circuits THz amplifiers for imaging, sensing, communications High gain at microwave frequencies precision analog design, high resolution ADC & DAC, high performance receivers Why THz Transistors?

4. We Wbc Tb Tc (emitter length Le) Bipolar transistor scaling laws To double cutoff frequencies of a mesa HBT, must: Keep constant all resistances and currents Reduce all capacitances and transit delays by 2 Epitaxial scaling Lateral scaling Ohmic contacts

5. We Wbc Wgap Base Access Resistance • Surface Depletion • Process Damage  Need for very small Wgap • Small undercut in InP emitter • Self-aligned base contact

6. Base-Emitter Short Undercut in thick emitter semiconductor Helps in Self Aligned Base Liftoff InP Wet Etch Slow etch plane Fast etch plane • For controlled semiconductor undercut • Thin semiconductor To prevent base – emitter short • Vertical emitter profile and line of sight metal deposition • Shadowing effect due to high emitter aspect ratio

7. Composite Emitter Metal Stack W emitter TiW W Erik Lind Evan Lobisser TiW emitter • W/TiW metal stack • Low stress • Refractory metal emitters • Vertical dry etch profile

8. Base Metal SiNx TiW BCB 100nm W FIB/TEM by E Lobisser Vertical Emitter Vertical etch profile Low stress High emitter yield Scalable emitter process

9. Dual SiN sidewall Controlled InP undercut Mo contact InGaAs cap InP emitter 50nm Narrow BE gap FIB/TEM by E Lobisser Narrow Emitter Undercut

10. Process flow Mo contact to n-InGaAs for emitter W/TiW/SiO2/Cr dep SF6/Ar etch SiNx Sidewall SiO2/Cr removal InGaAs Wet Etch Second SiNx Sidewall InP Wet Etch Base Contact Lift-off Base and collector formed via lift off and wet etch BCB used to passivate and planarize devices Self-aligned process flow for DHBTs

11. Epitaxial Design Vbe = 1 V, Vcb = 0.7 V, Je = 24 mA/mm2 Thin emitter semiconductor  Enables wet etching

12. Results - DC Measurements Common emitter I-V @Peak ft,fmax Je = 19.4 mA/mm2 P = 32 mW/mm2 BVceo = 3.7 V @ Je = 10 kA/cm2 β = 20 Base ρsh = 710Ω/sq, ρc < 5Ω·µm2 Collector ρsh = 15 Ω/sq, ρc = 22Ω·µm2 Gummel plot

13. 1-67 GHz RF Data Ic = 11.5 mA Vce = 1.66 V Je = 19.4 mA/mm2 Vcb = 0.7 V Single-pole fitto obtain cut-off frequencies

14. Parameter Extraction Jkirk = 23 mA/mm2 (@Vcb = 0.7V)

15. Equivalent Circuit Rex < 4 Wmm2 Hybrid-p equivalent circuit from measured RF data

16. TEM – Wide base mesa High Ac / Ae ratio (>5) High Rex . Ccb delay Low ft 0.2 mm 220 nm

17. Summary • Demonstrated DHBTs with peak ft/ fmax = 460/850 GHz • Small Wgap for reduced base access resistance  High fmax • Narrow sidewalls, smaller base mesa and better base ohmics needed to enable higher bandwidth devices

18. Thank You Questions? This work was supported by the DARPA THETA program under HR0011-09-C-006. A portion of this work was done in the UCSB nanofabrication facility, part of NSF funded NNIN network and MRL Central Facilities supported by the MRSEC Program of the NSF under award No. MR05-20415