185 GHz Monolithic Amplifier in InGaAs/InAlAs Transferred-Substrate HBT Technology

1. 185 GHz Monolithic Amplifier in InGaAs/InAlAs Transferred-Substrate HBT Technology M. Urteaga, D. Scott, T. Mathew, S. Krishnan, Y. Wei, M. Rodwell. Department of Electrical and Computer Engineering, University of California, Santa Barbara urteaga@ece.ucsb.edu 1-805-893-8044 IMS2001 May 2001, Phoenix, AZ

2. Outline IMS2001 UCSB • Introduction • Transferred-Substrate HBT Technology • Circuit Design • Results • Conclusion

3. 15 10 5 0 IMS2001 Transferred-Substrate HBTs • Substrate transfer allows simultaneous scaling of emitter and collector widths • Maximum frequency of oscillation • Sub-micron scaling of emitter and collector widths has resulted in record values for extrapolatedfmax (>1 THz) • Promising technology for ultra-high frequency tuned circuit applications 30 Mason's 3000 Å collector 400 Å base with 52 meV grading AlInAs / GaInAs / GaInAs HBT gain, U 25 20 MSG Gains, dB H f = 1.1 THz ?? 21 max Emitter, 0.4 x 6 mm2 f = 204 GHz t Collector, 0.7 x 6 mm2 I = 6 mA, V = 1.2 V c ce 10 100 1000 Frequency, GHz

4. IMS2001 Ultra-high Frequency Amplifiers • Applications for electronics in 140-220 GHz frequency band • Wideband communication systems • Atmospheric sensing • Automotive radar • Amplifiers in this frequency band realized in InP-based HEMT technologies • 3-stage amplifier with 30 dB gain at 140 GHz. Pobanz et. al., IEEE JSSC, Vol. 34, No. 9, Sept. 1999. • 3-stage amplifier with 12-15 dB gain from 160-190 GHz Lai et. al., 2000 IEDM, San Francisco, CA. • 6-stage amplifier with 20  6 dB from 150-215 GHz. Weinreb et. al., IEEE MGWL, Vol. 9, No. 7, Sept. 1999. • This Work: • Single-stage tuned amplifier with 3.0 dB gain at 185 GHz • First HBT amplifier in this frequency range • Gain-per-stage is comparable to HEMT technology

5. InGaAs 1E19 Si 1000 Å Grade 1E19 Si 200 Å InAlAs 1E19 Si 700 Å InAlAs 8E17 Si 500 Å Grade 8E17 Si 233 Å Grade 2E18 Be 67 Å InGaAs 4E19 Be 400 Å InGaAs 1E16 Si 400 Å InGaAs 1E18 Si 50 Å InGaAs 1E16 Si 2550 Å InAlAs UID 2500 Å S.I. InP IMS2001 InGaAs/InAlAs HBT Material System Layer Structure Band Diagram 2kT base bandgap grading Bias conditions for the band diagram Vbe = 0.7 V Vce = 0.9 V

6. Device Fabrication I IMS2001

7. IMS2001 Transferred-Substrate Process Flow • emitter metal • emitter etch • self-aligned base • mesa isolation • polyimide planarization • interconnect metal • silicon nitride insulation • Benzocyclobutene, etch vias • electroplate gold • bond to carrier wafer with solder • remove InP substrate • collector metal • collector recess etch

8. Device Fabrication II IMS2001

9. Ultra-high fmax Devices IMS2001 • Electron beam lithography used to define submicron emitters and collectors • Minimum feature sizes • 0.2 m emitter stripe widths • 0.3 m collector stripe widths • Improved collector-to-emitter alignment using local alignment marks • Future Device Improvements • Carbon base doping • na >1.0 x 1020 cm-3 • significant reduction in Rbb • DHBTs with InP Collectors • Greater than 6 V BVCEO 0.3 m Emitter before polyimide planarization 0.4 m Collector Stripe

10. Device Measurements IMS2001 DC Measurements Measured RF Gains • Device dimensions: • Emitter area: 0.4 x 6 m2 • Collector area: 0.7 x 6.4 m2 •  = 20 • BVCEO = 1.5 V • Bias Conditions: • VCE = 1.2 V, IC = 4.8 mA • f = 160 GHz • Measurements of unilateral power gain in 140-220 GHz frequency band appear to show unphysical behavior

11. Amplifier Design IMS2001 Simulation Results • Simple common-emitter design conjugately matched at 200 GHz using shunt-stub tuning • Shunt R-C network at output provides low frequency stabilization • Simulations predicted 6.2 dB gain • Designed using hybrid-pi model derived from DC-50 GHz measurements of previous generation devices • Electromagnetic simulator (Agilent’s Momentum) was used to characterize critical passive elements S21 S11, S22 Circuit Schematic

12. IMS2001 Design Considerations in Sub-mmwave Bands • Transferred-substrate technology provides low inductance microstrip wiring environment • Ideal for Mixed Signal ICs • Advantages for MMIC design: • Low via inductance • Reduced fringing fields • Disadvantages for MMIC design: • Increased conductor losses • Resistive losses are inversely proportional to the substrate thickness for a given Zo • Amplifier simulations with lossless matching network showed 2 dB more gain • Possible Solutions: • Use airbridge transmission lines • Find optimum substrate thickness

13. IMS2001 140-220 GHz VNA Measurements • HP8510C VNA used with Oleson Microwave Lab mmwave Extenders • Extenders connected to GGB Industries coplanar wafer probes via short length of WR-5 waveguide • Internal bias Tee’s in probes for biasing active devices • Full-two port T/R measurement capability • Line-Reflect-Line calibration performed using on-wafer transmission line standards UCSB 140-220 GHz VNA Measurement Set-up

14. IMS2001 Amplifier Measurements • Measured 3.0 dB peak gain at 185 GHz • Device dimensions: • Emitter area: 0.4 x 6 m2 • Collector area: 0.7 x 6.4 m2 • Device bias conditions: • Ic= 3.0 mA, VCE = 1.2 V Measured Gain Measured Return Loss Cell Dimensions: 690m x 350 m

15. IMS2001 Simulation vs. Measurement Simulation versus Measured Results • Amplifier designed for 200 GHz • Peak gain measured at 185 GHz • Possible sources for discrepancy: • Matching network design • Device model

16. IMS2001 Matching Network Design Matching Network Breakout Simulation Vs. Measurement • Breakout of matching network without active device was measured on-wafer • Measurement compared to circuit simulation of passive components • Simulations show good agreement with measurement • Verifies design approach of combining E-M simulation of critical passive elements with standard microstrip models S21 S11 S22 Red- Simulation Blue- Measurement

17. IMS2001 Device Modeling I: Hybrid-Pi Model HBT Hybrid-Pi Model Derived from DC-50 GHz Measurements • Design used a hybrid-pi device model based on DC-50 GHz measurements • Measurements of individual devices in 140-220 GHz band show poor agreement with model • Discrepancies may be due to weakness in device model and/or measurement inaccuracies • Device dimensions: • Emitter area: 0.4 x 6 m2 • Collector area: 0.7 x 6.4 m2 • Bias Conditions: • VCE = 1.2 V, IC = 4.8 mA

18. IMS2001 Device Modeling II: Model vs. Measurement S21 • Measurements and simulations of device S-parameters from 6-45 GHz and 140-220 GHz • Large discrepancies in S11 and S22 • Anomalous S12 believed to be due to excessive probe-to-probe coupling • Red- Simulation • Blue- Measurement S11, S22 S12

19. IMS2001 Simulation vs. Measurement UCSB Simulation versus Measured Results Simulation Using Measured Device S-parameters • Simulated amplifier using measured device S-parameters in the 140-220 GHz band • Simulations show better agreement with measured amplifier results • Results point to weakness in hybrid-pi model used in the design • Improved device models are necessary for better physical understanding but measured S-parameter can be used in future amplifier designs

20. Conclusions IMS2001 UCSB • Demonstrated first HBT amplifier in the 140-220 GHz frequency band • Simple design provides direction for future high frequency MMIC work in transferred-substrate process • Observed anomalies in extending hybrid-pi model to higher frequencies Future Work • Multi-stage amplifiers and oscillators • Improved device performance for higher frequency operation Acknowledgements This work was supported by the ONR under grant N0014-99-1-0041 And the AFOSR under grant F49620-99-1-0079