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 IMS2001 May 2001, Phoenix, AZ

Outline IMS2001UCSB Introduction Transferred-Substrate HBT Technology Circuit Design Results Conclusion

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 extrapolated f max (>1 THz) Promising technology for ultra-high frequency tuned circuit applications Gains, dB Frequency, GHz f max = 1.1 THz ?? f  = 204 GHz Mason's gain, U H 21 MSG Emitter, 0.4 x 6  m 2 Collector, 0.7 x 6  m 2 I c = 6 mA, V ce = 1.2 V IMS Å collector 400 Å base with 52 meV grading AlInAs / GaInAs / GaInAs HBT

Ultra-high Frequency AmplifiersIMS2001 Applications for electronics in 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  3-stage amplifier with dB gain from GHz Lai et. al., 2000 IEDM, San Francisco, CA.  6-stage amplifier with 20  6 dB from GHz. Weinreb et. al., IEEE MGWL, Vol. 9, No. 7, Sept 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

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 Bias conditions for the band diagram V be = 0.7 V V ce = 0.9 V InGaAs/InAlAs HBT Material SystemIMS2001 Layer StructureBand Diagram 2kT base bandgap grading

Device Fabrication I IMS2001

Transferred-Substrate Process FlowIMS2001 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

Device Fabrication II IMS2001

Ultra-high f max Devices 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  n a >1.0 x cm -3  significant reduction in R bb DHBTs with InP Collectors  Greater than 6 V BV CEO IMS  m Emitter before polyimide planarization 0.4  m Collector Stripe

Device Measurements IMS2001 DC MeasurementsMeasured RF Gains Device dimensions:  Emitter area: 0.4 x 6  m 2  Collector area: 0.7 x 6.4  m 2  = 20 BV CEO = 1.5 V Bias Conditions:  V CE = 1.2 V, I C = 4.8 mA f  = 160 GHz Measurements of unilateral power gain in GHz frequency band appear to show unphysical behavior

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 Simulation Results S21 Circuit Schematic S11, S22 Amplifier Design IMS2001

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 Z o Amplifier simulations with lossless matching network showed 2 dB more gain Possible Solutions:  Use airbridge transmission lines  Find optimum substrate thickness IMS2001 Design Considerations in Sub-mmwave Bands

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 GHz VNA MeasurementsIMS2001 UCSB GHz VNA Measurement Set-up

Amplifier Measurements Measured 3.0 dB peak gain at 185 GHz Device dimensions:  Emitter area: 0.4 x 6  m 2  Collector area: 0.7 x 6.4  m 2 Device bias conditions:  I c = 3.0 mA, V CE = 1.2 V Measured Gain Measured Return Loss IMS2001 Cell Dimensions: 690  m x 350  m

Amplifier designed for 200 GHz Peak gain measured at 185 GHz Possible sources for discrepancy:  Matching network design  Device model Simulation versus Measured Results Simulation vs. MeasurementIMS2001

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 Matching Network Breakout Simulation Vs. Measurement S21 S22 S11 Red- Simulation Blue- Measurement Matching Network DesignIMS2001

Design used a hybrid-pi device model based on DC-50 GHz measurements Measurements of individual devices in 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  m 2  Collector area: 0.7 x 6.4  m 2 Bias Conditions:  V CE = 1.2 V, I C = 4.8 mA HBT Hybrid-Pi Model Derived from DC-50 GHz Measurements Device Modeling I: Hybrid-Pi ModelIMS2001

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

Simulated amplifier using measured device S-parameters in the 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 Simulation versus Measured Results Simulation Using Measured Device S-parameters Simulation vs. MeasurementIMS2001UCSB

Conclusions IMS2001UCSB Demonstrated first HBT amplifier in the 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 N And the AFOSR under grant F