2002 ECOC Conference, September, Copenhagen 50-200 GHz InP HBT Integrated Circuits for Optical Fiber and mm-Wave Communications Mark Rodwell University of California, Santa Barbara [email protected] 805-893-3244,
Download ReportTranscript 2002 ECOC Conference, September, Copenhagen 50-200 GHz InP HBT Integrated Circuits for Optical Fiber and mm-Wave Communications Mark Rodwell University of California, Santa Barbara [email protected] 805-893-3244,
2002 ECOC Conference, September, Copenhagen 50-200 GHz InP HBT Integrated Circuits for Optical Fiber and mm-Wave Communications Mark Rodwell University of California, Santa Barbara [email protected] 805-893-3244, 805-893-3262 fax Electronics for GigaHertz Commun Applications: optical fiber transceivers at 40 Gb/s and higher Wideband Optical Transceiver Key advantages for: TIA, LIA, Modulator driver addr dete O/E, E/O interfaces A DMUX D Losing competition with SiGe: MUX/CMU, DMUX/CDR excessive power problems with integration scale PLL rout clock MUX Wideband mm-Wave Transceiver mm-wave interfaces 80 & 160 Gb may come in time world may not need capacity for some time WDM might be better use of fiber bandwidth I Q A D PLL DMUX I Q A DMUX D power amplifier D I Q A I MUX D A Q This presentation: how InP HBT ICs will be able to do 160 Gb/s "If you build it, they will come." (today, this argument is not convincing). S n d o mmWave Transmission UCSB 1 (Weather permitting) 1 km Sea level 0.1 Log Transmission Atmospheric attenuation is LOW (~4 dB/km) at bands of interest 60-80 GHz, 120-160 GHz, 220-300 GHz 0.01 1E-3 1E-4 1E-5 1E-6 0.0 0.2 0.4 0.6 0.8 1.0 Frequency, THz Geometric path losses are LOW due to short wavelengths. 4 mW transmitter power sufficient for 10 Gb/s transmission over 500 meters range given 20 cm diameter antennas Bit rate carrier frequency F Distance atmospheric loss Dant, trans Dant, rcvr bits/symbol kT Prec ∆f transmission atmospheric loss Ptransmitter 1.00E+10 1/sec 1.50E+11 Hz 10 dB 5.00E+02 m 4.00E-03 dB/m 0.2 m 0.2 m 1 -173.83 dBm (1Hz) -48.27 dBm 1.00E+10 Hz -51.64 2 dB 3.4 mW receiver noise figure transmission range dB loss per unit distance transmit antenna diameter receive antenna diameter received power at 10^{-9} B.E.R RF channel bandwidth required geometric path loss, dB total atmospheric loss, dB required transmitter power How Do We Improve the Bandwidth of Bipolar Transistors ? kT 1 kT base collector C je Cbc Rex Rcoll 2f qI E qI E Thinner base, thinner collector higher f , but higher RbbCcb , RexCcb … what parameters are really important in HBTs ? how do we improve HBT performance ? Rodwell HBT scaling: layer thicknesses 2:1 improved device speed: keep G's, R's, I's, V's constant, reduce 2:1 all C's, WE WEB LE emitter base x reduce Tb by 2:1 b improved 2:1 reduce Tc by 2:1 c improved 2:1 note that Ccb has been doubled ..we had wanted it 2:1 smaller base collector WC WBC b Tb2 / 2 Dn b Tc / 2vsat Assume WC ~ WE 's Rodwell HBT scaling: lithographic dimensions 2:1 improved device speed: keep G's, R's, I's, V's constant, reduce 2:1 all C's, Rbb Rgap Rspread Rcontact Base Resistance Rbb must remain constant Le must remain ~ constant Rcontact sheet c ,vertical 2 LE Ccb/Area has been doubled ..we had wanted it 2:1 smaller …must make area=LeWe 4:1 smaller must make We & Wc 4:1 smaller WE WEB LE emitter base x reduce collector width 4:1 reduce emitter width 4:1 keep emitter length constant 's base collector WC WBC Assume WC ~ WE HBT scaling: emitter resistivity, current density 2:1 improved device speed: keep G's, R's, I's, V's constant, reduce 2:1 all C's, 's Rodwell Emitter Resistance Rex must remain constant but emitter area=LeWe is 4:1 smaller resistance per unit area must be 4:1 smaller Assume WC ~ WE Collector current must remain constant but emitter area=LeWe is 4:1 smaller and collector area=LcWc is 4:1 smaller current density must be 4:1 larger WE WEB LE emitter base increase current density 4:1 reduce emitter resistivity 4:1 x base collector WC WBC Rodwell, IEEE Trans. Electron Devices, Nov. 2001 Scaling Laws for fast HBTs Required proportion al change in HBT parameters in order to obtain a : 1 increase in bandwidth in an arbitrary circuit For some device structures , but not all , the base contact resistivit y v ( - cm 2 ) must also scale as 2 Electronics for GigaHertz Communication Optical Transmitters / Receivers are Mixed-Signal ICs Wideband Optical Transceiver address detect O/E, E/O interfaces buffer A DMUX D PLL Switch route clock MUX Wideband mm-Wave Transceiver TIA: small-signal mm-wave interfaces LIA: often limiting A D Rc Rc PLL I Q power amplifier Q1 DMUX D Rf Q2 DMUX I Q A Rf Q2 I2 I2 I1 I Q Q1 electronic MUX/CMU & DMUX/CDR: or optical mostly digital D A I MUX Switches: network protocols, digital control, fast ICs, optical, electronic switches I1 D A Q Small-signal cutoff frequencies (f, fmax) are ~ predictive of analog speed Limiting and digital speed much more strongly determined by (I/C) ratios InP HBT has been well-optimized for f & fmax, less well for digital speed How do we improve logic speed ? Gate Delay Determined by : out Depletion capacitanc e charging through the logic swing VLOGIC Ccb Cbe,depletion IC Depletion capacitanc e charging through the base resistance Rbb Ccb Cbe,depletion Supplying base collector stored charge through the base resistance IC Rbb b c VLOGIC The logic swing must be at least VLOGIC kT 6 Rex I c q out in in clock clock clock clock Delay not well correlated with f . VLOGIC I C Ccb Cbe,depl is 60% - 80% of total. High I C / Ccb is a key HBT design objective. Acollector TC Aemitter 2veffective Rex must be very low for low Vlogic at high J e Ccb VLOGIC VLOGIC IC 2VCE ,min InP logic barely faster tha n SiGe : need to design for clock speed, not f & f max Technology Roadmaps for 40 / 80 / 160 Gb/s Challenges with Scaling: Collector-base scaling Mesa HBT: collector under base contacts. Base contacts have nonzero resistivity → sets minimum contact size Solution: reduce base contact resistivity Solution: decouple base & collector dimensions e.g. buried SiO2 in junction (SiGe), undercut-mesa (InP) Emitter Ohmic Resistivity: must improve in proportion to square of speed improvements Current Density: increases rapidly device heating, current-induced dopant migration, dark-line defect formation SiGe at 5*105 A/cm2, InP at 1*105 Loss of breakdown voltage InP superior to SiGe at equal speed Yield InP HBT processes must reach yield sufficient for DMUX/CMU progressively more difficult at submicron dimensions Low Ccb InP HBT structures transferred-substrate Allows deep submicron collector scaling high mm-wave gains low yield at deep submicron scaling mm-wave device, not mixed-signal undercut-collector emitter base contact undercut collector junction InGaAs collector InGaAs base InP collector collector contact InGaAs subcollector InP subcollector Pursued by several research groups Also has uncertain yield at submicron geometries SI substrate Narrow-mesa with ~1E20 carbon-doped base The conservative III-V device structure Yet, I assert that even this device is not viable of mass manufacturing if > 3000 transistors per IC are sought Need improved device structures for high yield at 0.1 mm scaling Transferred-Substrate HBTs UCSB ONR 220 GHz On-Wafer Network Analysis Miguel Urteaga 140-220 GHz network analysis HP8510C network analyzer & Oleson Microwave Lab frequency Extenders GGB waveguide-coupled probes 75-100 GHz network analysis GGB waveguide-coupled probes HP W-band test set 1-50 GHz network analysis GGB coax-connectorized probes HP 0.045-50 GHz test set Accurate measurements are not easy HBT Ccb is very small (~5 fF) → S12 easily masked by probe-probe coupling increase probe separation: reference plane extensions On-wafer LRL calibration standards ultra-thin microstrip for reduced mode coupling Submicron InAlAs/InGaAs HBTs: Unbounded (?!?) Unilateral power gain 45-170 GHz UCSB ONR Miguel Urteaga 40 unbounded U 35 30 U emitter RF Gains 25 20 15 MAG/MSG h21 10 5 0 -5 1E10 1E11 1E12 collector Freq. Emitter: 0.3 x 18 mm2, Collector: 0.7 x 18.6 mm2 Ic = 5 mA, Vce = 1.1 V gain resonances likely due to IMPATT effects Rodwell, Int. Symp. Compound Semiconductors, Tokyo, Oct. 2001 Urteaga, Int. Journal High Speed Electronics and Systems, to be published UCSB 175 GHz Single-Stage Amplifier Miguel Urteaga 10 S21 S11 S22 50 0.2pF 5 80 1.2ps 30 0.2ps 80 1.2ps 50 30 1.2ps 0 50 0.6ps dB IN OUT -5 -10 -15 -20 140 150 160 170 180 190 200 Freq. (GHz) 6.3 dB gain at 175 GHz 210 220 Deep Submicron Bipolar Transistors for 140-220 GHz Amplification Transistor Gains, dB 30 unbounded U U U 20 MSG/MAG 10 H 21 0 10 100 1000 Frequency, GHz 8 6 4 S21, dB Miguel Urteaga raw 0.3 mm transistor: 6-11 dB power gain @ 200 GHz 40 2 -2 1-transistor amplifier: 6.3dB @ 175 GHz -4 140 150 0 160 170 180 190 200 210 220 Frequency, GHz 10 gain, dB UCSB 0 -10 -20 -30 140 3-transistor amplifier: 8 dB @ 195 GHz 150 160 170 180 190 Frequency (GHz) 200 210 220 UCSB InGaAs/InP DHBT, 3000 Å InP collector Sangmin Lee 2 40 I step = 20 mA fmax = 462 GHz, ft = 139 GHz b Gains (dB) 1 C I (mA) 30 BVCEO = 8 V at JE =5*104 A/cm2 2 4 V CE 6 (V) 20 343 395 10 0 0 U 8 h21 139 462 0 1 10 100 1000 Frequency (GHz) 0.5 mm x 8 mm emitter (mask) 0.4 mm x 7.5 mm emitter (junction) 1.0 mm x 8.75 mm collector High Current, High Breakdown Voltage InP DHBT 140 A =128 um 120 2 E 14 12 10 80 Ic, m A Ic, mA 100 60 8 6 4 40 2 0 -1 20 0 1 2 3 4 5 6 7 Vcb, V 0 0 2 4 6 8 10 Vcb, V 30 AE=128um2 U, MSG/MAG, dB 25 8-finger device 8 x ( 1 mm x 16 mm emitter ) 8 x ( 2 mm x 20 mm collector ) IC=100mA 20 15 Vcb=2.9V MSG/MAG U 10 5 0 0 10 fmax=330 GHz 10 1 10 2 Frequency, GHz 10 3 ARO MURI UCSB W band 128 mm2 power amplifier common base PA 0.5mm x 0.4 mm, AE=128 mm2 Bias: Ic=78 mA, Vce=3.6 V 20 10 10 S21 GT 5 8 10 6 5 4 0 2 S11 -15 T -10 -20 -25 -30 80 90 frequency, GHz 100 110 G , dB -5 Pout, dBm S22 0 S11, S21, S22 Pout 15 -5 0 -15 -10 -5 0 5 10 Pin, dBm f0=85 GHz, BW3dB=28 GHz,GT=8.5 dB, P1dB=14.5 dBm, Psat=16dBm 15 High Speed Amplifiers 18 dB, DC--50+ GHz 20 S21 15 >397 GHz gain x bandwidth from 2 HBTs 10 5 0 S11 -5 -10 S22 -15 -20 0 10 20 30 40 50 8.2 dB, DC-80 GHz 10 Gains, dB S 21 5 0 S -5 11 -10 S 22 -15 0 10 20 30 40 50 Frequency, GHz 60 70 80 UCSB Dino Mensa PK Sundararajan Ultra Wideband Mesa InP/InGaAs/InP DHBTs UCSB / IQE Mattias Dahlstrom (UCSB) Amy Liu (IQE) 30 500 Ohm/square base sheet resistance < 2*10-7 Ohm-cm2 base contact resistance 25 21 Gain (dB) H , U 2000 Å InP collector 300 Å InGaAs base 8E19 to 5E19 graded C base doping InAlAs/InGaAs base-collector grade. 20 15 f =282 GHz t 10 f =480 GHz max 5 0 10 7.5 V Breakdown 282 GHz f >450 GHz fmax, operation to 500 kA/cm2 at 1.7 volts 10 10 11 frequency (GHz) 10 12 87 GHz HBT master-slave latch UCSB PK Sundararajan, Zach Griffith 200 GHz logic program InAlAs /InGaAs/InP MESA DHBT 400 Å base, 2000 Å collector, 9 V BVCEO 200 GHz ft, 180 GHz fmax 2.5 x 105 A/cm2 operation 87 GHz input, 43.5 GHz output -0.06 -0.08 V out (Volts) -0.1 -0.12 -0.14 -0.16 -0.18 -0.2 22 22.02 22.04 22.06 22.08 time (nsec) 22.1 22.12 22.14 8 GHz S ADC UCSB PK Sundararajan, Zach Griffith 200 GHz logic program Technology 0.7 um InAlAs /InGaAs/InP MESA DHBT 400 Å base, 2000 Å collector, 9 V BVCEO, 200 GHz ft, 180 GHz fmax 2.5 x 105 A/cm2 operation Design simple 2nd-order gm-C topology comparator is 87 GHz MSS latch integration by capacitive loads 3-stage comparator, RTZ gated DAC Results 133 dB (1 Hz) SNR at 74 MHz equivalent to ~8.8 bits at 200 MS/s 975 kHz FFT bin size 8 GHz clock rate 65.5 MHz signal 64:1 oversampling ratio InP vs. Si/SiGe HBTs: recent experience at 40 Gb/s 40 Gb/s IC development during internet bubble 7 of my ex-Ph.D. students involved, at 4 different companies personally actively involved as consultant InP HBT technology 1 mm design-rule processes easily developed, good reliability, yield ok for 2000 HBTs (not more), 170 GHz f, fmax , 7 volt Vbr, 3 mA (min) device, 60 GHz clock Resulting ICs TIA, LIA, 6 V differential modulator driver: quite successful MUX/CMU, DMUX/CDR: limited to 4:1 (yield, power) SiGe necessary for 16:1 standards-compliant MUX & DMUX market is presently very small InP requires lower NRE than SiGe InP critically needs: higher integration scales, scaling for speed & power Very strong features of SiGe-bipolar transistors High current density 10 mA/mm2 T-shaped polysilicon emitter 0.25 mm junction wide contact low resistance, high yield Thin intrinsic base: low b Thick extrinsic base: low Rbb Low Ccb collector junction collector pedestal CVD/CMP SiO2 planarization regrown poly extrinsic base High-yield, planar processing high levels of integration LSI and VLSI capabilities SiGe clock rates up to 65 GHz Much more complex ICs than feasible in InP HBT InP HBT must reach higher integration scales or will cease to compete InP vs. Si/SiGe HBTs: materials vs. scaling advantages Advantages of InP ~20:1 lower base sheet resistance, ~5:1 higher base electron diffusivity ~3:1 higher collector electron velocity, ~4:1 higher breakdown-at same f. Disadvantage of InP: archaic mesa fabrication process Presently only scaled to ~ 1 um (production) large emitters, poor emitter contact: low current density: 2 mA/um2 high collector capacitance nonplanar device - low yield low integration scales InP HBT limits to yield: non-planar process Emitter contact Failure modes liftoff failure: emitter-base short-circuit emitter base contact base base sub collector S.I. substrate sub collector S.I. substrate Etch to base base excessive emitter undercut sub collector base contact S.I. substrate base Liftoff base metal base contact emitter contact sub collector base contact S.I. substrate base sub collector S.I. substrate planarization failure: interconnect breaks Emitter planarization, interconnects base base sub collector S.I. substrate sub collector S.I. substrate Yield degrades as emitters are scaled to submicron dimensions MBE growth of Polycrystalline n+ InAs Dennis Scott SiGe HBT process: extensive use of non-selective-area poly-Si regrowth Can a similar technology be developed for InP ? Polycrystalline InAs grown on SiN: • Doping = 1.3 1019 cm-3, Mobility = 620 cm2/V•s Poly InAs:Si Doping vs. Temp 19 2.2 10 2 10 • Results in doping-mobility product of 81021 (V •s •cm)-1 19 1.8 10 19 Doping InGaAs lattice matched to InP: • Doping = 1.0 1019 cm-3, Mobility = 2200 cm2/V•s • Results in doping-mobility product of 221021 (V •s •cm)-1 19 1.6 10 19 1.4 10 19 1.2 10 1 10 19 8 10 18 6 10 18 945 950 955 960 965 Temp Polycrystalline InAs has potential as an extrinsic emitter contact. 970 975 980 985 1) Epitaxial Growth, Fe implant isolation Process Flow: Single-polyregrowth InP HBT 2) Deposit Pd/W base Ohmics. Encapsulate with Si3N4 Etch base-collector junction base base N- collector N- collector N+ subcollector N+ subcollector S.I. substrate S.I. substrate 3) Passivate with Si3N4 Etch emitter window through base Form emitter SiN sidewalls top view emitter junction extrinsic emitter and contact 4) Regrow polycrystalline emitter. Deposit emitter metal. Etch through emitter emitter contact regrown InAlAs/InAs emitter* Si N 3 4 base contact Si N 3 4 base contact N- collector N+ subcollector N- collector S.I. substrate collector contact N+ subcollector S.I. substrate 5) Recess etch and deposit collector contacts emitter contact regrown InAlAs/InAs emitter* Si N 3 4 base contact collector contact base contact base contact Si N 3 4 subcollector isolation implant mask N- collector N+ subcollector S.I. substrate *monocrystalline where grown on semiconductor, polycrystalline where grown on silicon nitride Regrown-Poly-InAs-Emitter HBT 1 1.0 10 AE = 0.8 x 15 um 2 I b = 100uA/step 0 0 6.0 10 c I (mA) 8.0 10 0 4.0 10 0 2.0 10 0 0.0 10 0 1 2 V ce 3 4 (V) Ib, Ic (mA) 2 10 2 10 1 10 0 10 -1 10 -2 10 -3 10 -4 Gummel for 0.8x15 um Emitter Ic Ib 0 0.2 0.4 0.6 0.8 Vbe (volts) 1 1.2 Dennis Scott Submicron Scaling of InP HBTs InP HBTs are a mixed-signal, not a MIMIC technology for MIMICs, sub-0.1-mm InP HEMTs are hard to beat mixed-signal is fiber ICs, ADCs, DACs, digital frequency synthesis these are 1000 -- 40,000 transistor ICs InP HBTs are struggling to compete with SiGe HBT application demands transistor counts near/beyond yield limits large emitter junctions→ high current → power near acceptable limits no decisive speed advantage in relevant circuits: digital logic materials advantages being squandered by inadequate scaling InP HBTs can be scaled to operate at 160 Gb/s key is scaling emitter to 0.2 mm, collector to 0.4 mm contact resistivities challenging but feasible; yield is key concern Critically needed for InP HBTs highly scaled process: 0.2 mm emitters, 0.4 mm collectors highly planar and high-yield fabrication processes small emitter junctions (0.2 mm x 0.5 mm) for acceptable power In Case of Questions What HBT parameters determine logic speed ? Cje V/ I V/ I (kT/q) I Rex Rbb total Ccbx 33.5% 1.4% -1.3% 10.2% 43.8% b+c ) ( I/V) Ccbi 6.7% 0.1% 0.1% 6.8% 38% total 27.8% 0.4% 0.3% 2.8% 31.3% 68.4% 12.3% 2.5% 0.1% 16.7% 100.0% 12.3% 0.5% 0.9% 3.7% 17.5% Sorting Delays by capacitanc es : 44% charging C je , 38% charging Ccb , only 18% charging Cdiff (e.g. b c ) Sorting Delays by resistance s and transit t imes : 68% from Vlogic / I c , 12% from ( b c ), 17% from Rbb Rex has very strong indirect effect, as Vlogic 6 kT / q I C Rex Caveats: assumes a specific UCSB InP HBT (0.7 um emitter, 1.2 um collector 2kÅ thick, 400 Å base, 1.5E5 A/cm^2) ignores interconnect capacitance and delay, which is very significant Yoram Betser, Raja Pullela Accurate Transistor Measurements Are Not Easy • Submicron HBTs have very low Ccb (< 5 fF) • HBT S12 is very small 230 mm 230 mm • Standard 12-term VNA calibrations do not correct S12 background error due to probe-to-probe coupling Solution Embed transistors in sufficient length of transmission line to reduce coupling Transistor in Embedded in LRL Test Structure Place calibration reference planes at transistor terminals Line-Reflect-Line Calibration Standards easily realized on-wafer Does not require accurate characterization of reflect standards Characteristics of Line Standards are well controlled in transferred-substrate microstrip wiring environment Corrupted 75-110 GHz measurements due to excessive probe-to-probe coupling Can we trust the calibration ? Miguel Urteaga 75-110 GHz calibration looks Great 140-220 GHz calibration looks OK S11 of open About 0.1 dB / 3o error S11 of through About –40 dB S11 of short S11 of through S11 of open freq (75.00GHz to 110.0GHz) freq (140.0GHz to 220.0GHz) 0.30 Probe-Probe coupling is better than –45 dB -40 -45 0.25 S21 of through line is off by less than 0.05 dB 0.20 0.15 0.10 -50 0.05 -55 0.00 -60 -0.05 -0.10 -65 -0.15 -70 140 75 80 85 90 95 freq, GHz 100 105 150 160 170 180 110 freq, GHz 190 200 210 220 Negative Unilateral Power Gain ??? Can U be Negative? YES, if denominator is negative This may occur for device with a negative output conductance (G22) or some positive feedback (G12) U Y21 Y12 2 4G11G 22 G 21G12 What Does Negative U Mean? Device with negative U will have infinite Unilateral Power Gain with the addition of a proper source or load impedance 2-port Network AFTER Unilateralization • Network would have negative output resistance • Can support one-port oscillation • Can provide infinite two-port power gain U Y21 Y12 GL 2 4G11 G 22 G L G 21G12 Select GL such that denominator is zero: U Simple Hybrid- HBT model will NOT show negative U Rodwell Scaling Laws, Collector Current Density, Ccb charging time Collector Field Collapse (Kirk Effect) Vcb ( J / vsat qN d )(Tc2 / 2 ) base emitter sub collector collector Collector Depletion Layer Collapse Vcb,min (qN d )(Tc2 / 2 ) base emitter sub collector collector J max 2vsat (Vcb Vcb,min 2 ) / Tc2 Note that Vbe , hence (Vcb ) Vce Ccb VLOGIC / I C Acollector Tc VLOGIC VLOGIC Acollector TC IC VCE VCE ,min Aemitter 2vsat Collector capacitance charging time is reduced by thinning the collector while increasing current Why isn't base+collector transit time so important ? Under Small - Signal Operation : Q base dI C ( b c ) I C ( b c )I C ( b c ) Vbe Vbe dVbe kT / q Under Large - Signal Operation : Q base ( b c ) I dc ( b c ) I C VLOGIC VLOGIC Large - signal diffusion capacitanc e reduced by ratio of VLOGIC , which is ~ 10 : 1 kT / q Depletion capacitanc es see no such reduction HBT distributed amplifier AFOSR 11 dB, DC-87 GHz 15 S 10 21 Gains, dB 5 0 -5 S -10 S -15 22 11 -20 0 20 40 60 Frequency, GHz 80 TWA with internal ft-doubler cells UCSB PK Sundararajan