Miguel Urteaga

Submicron scaling of HBTs

The variation of heterojunction bipolar transistor (HBT) bandwidth with scaling is reviewed. High bandwidths are obtained by thinning the base and collector layers, increasing emitter current density, decreasing emitter contact resistivity, and reducing the emitter and collector junction widths. In mesa HBTs, minimum dimensions required for the base contact impose a minimum width for the collector junction, frustrating device scaling. Narrow collector junctions can be obtained by using substrate transfer or collector-undercut processes or, if contact resistivity is greatly reduced, by reducing the width of the base ohmic contacts in a mesa structure. HBTs with submicron collector junctions exhibit extremely high f/sub max/ and high gains in mm-wave ICs. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency f/sub max/ is 1.1 THz. f/sub max/ will be less than 1 THz if unmodeled electron transport physics produce a >20 dB/decade variation in power gain at frequencies above 110 GHz. Transferred-substrate HBTs have obtained 295 GHz f/sub T/. The substrate transfer process provides microstrip interconnects on a low-/spl epsiv//sub r/ polymer dielectric with a electroplated gold ground plane. Important wiring parasitics, including wiring capacitance, and ground via inductance are substantially reduced. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz and per-stage gain-bandwidth products over 400 GHz, and master-slave latches operating at 75 GHz.

InP HBT IC Technology for Terahertz Frequencies: Fundamental Oscillators Up to 0.57 THz

We report on the development of a 0.25-μm InP HBT IC technology for lower end of the THz frequency band (0.3-3 THz). Transistors demonstrate an extrapolated fmax of >;800 GHz while maintaining a common-emitter breakdown voltage (BVCEO) >;4 V. The transistors have been integrated in a full IC process that includes three-levels of interconnects, and backside processing. The technology has been utilized for key circuit building blocks (amplifiers, oscillators, frequency dividers, PLL, etc), all operating at ≥300 GHz. Next, we report a series of fundamental oscillators operating up to 0.57 THz fabricated in a 0.25-μm InP HBT technology. Oscillator designs are based on a differential series-tuned topology followed by a common-base buffer, in a fixed-frequency or varactor-tuned scheme. For ≥400 GHz designs, a subharmonic down-conversion mixer is integrated to facilitate spectrum measurement. At optimum bias, the measured output power was -6.2, -5.6, and -19.2 dBm, for 310.2-, 412.9-, and 573.1-GHz designs, respectively, with PDC ≤ 115 mW. Varactor-tuned designs demonstrated 10.6-12.3 GHz of tuning bandwidth up to 300 GHz.

SCALING OF InGaAs/InAlAsHBTs FOR HIGH SPEED MIXED-SIGNAL AND mm-WAVE ICs

High bandwidths are obtained with heterojunction bipolar transistors by thinning the base and collector layers, increasing emitter current density, decreasing emitter contact resistivity, and reducing the emitter and collector junction widths. In mesa HBTs, minimum dimensions required for the base contact impose a minimum width for the collector junction, frustrating device scaling. Narrow collector junctions can be obtained by using substrate transfer processes, or -if contact resistivity is greatly reduced -by reducing the width of the base Ohmic contacts in a mesa structure. HBTs with submicron collector junctions exhibit extremely high fmax and high gains in mm-wave ICs. Logic gate delays are primarily set by depletion-layer charging times, and neither fτ nor fmax is indicative of logic speed. For high speed logic, epitaxial layers must be thinned, emitter and collector junction widths reduced, current density increased, and emitter parasitic resistance decreased. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency fmax is 1.1 THz. Transferred-substrate HBTs have obtained 295 GHz fτ. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz, 66 GHz master-slave flip-flops, and 18 GHz clock rate Δ-Σ ADCs.

130nm InP DHBTs with ft >0.52THz and f max >1.1THz

We report results from a 130nm Indium Phosphide (InP) double heterojunction bipolar transistor (DHBT) technology. A 0.13×2µm² transistor exhibits a current gain cutoff frequency ft >520GHz, with a simultaneous extrapolated power gain cutoff frequency f<inf>max</inf>>1.1THz. The HBTs exhibit these RF figures-of-merit while maintaining a common-emitter breakdown voltage BV<inf>CEO</inf>=3.5V (J<inf>E</inf>=10µA/µm²). Additionally, scaling of the emitter junction length to 2µm enables high device performance at low total power levels. Transistors in the InGaAs/InP material system have demonstrated the highest reported transistor RF figures-of-merit. Previous published results include strained-InGaAs channel high-electron mobility transistors (HEMTs) with f<inf>max</inf> of >1THz [1,2], and InP DHBTs with f<inf>max</inf> >800GHz [3]. High bandwidth DHBTs have applications in a number of RF and mixed-signal applications due to their high power handling and high levels of integration relative to HEMTs. The HBTs reported in this work are designed for transceiver applications at the lower end of the THz frequency band [0.3–3 THz].

G-band (140-220 GHz) and W-band (75-110 GHz) InP DHBT medium power amplifiers

We report common-base medium power amplifiers designed for G-band (140-220 GHz) and W-band (75-110 GHz) in InP mesa double HBT technology. The common-base topology is preferred over common-emitter and common-collector topologies due to its superior high-frequency maximum stable gain (MSG). Base feed inductance and collector emitter overlap capacitance, however, reduce the common-base MSG. A single-sided collector contact reduces Cce and, hence, improves the MSG. A single-stage common-base tuned amplifier exhibited 7-dB small-signal gain at 176 GHz. This amplifier demonstrated 8.7-dBm output power with 5-dB associated power gain at 172 GHz. A two-stage common-base amplifier exhibited 8.1-dBm output power with 6.3-dB associated power gain at 176 GHz and demonstrated 9.1-dBm saturated output power. Another two-stage common-base amplifier exhibited 11.6-dBm output power with an associated power gain of 4.5 dB at 148 GHz. In the W-band, different designs of single-stage common-base power amplifiers demonstrated saturated output power of 15.1 dBm at 84 GHz and 13.7 dBm at 93 GHz

Wideband DHBTs using a graded carbon-doped InGaAs base

We report an InP/InGaAs/InP double heterojunction bipolar transistor (DHBT), fabricated using a mesa structure, exhibiting 282 GHz f/sub /spl tau// and 400 GHz f/sub max/. The DHBT employs a 30 nm InGaAs base with carbon doping graded from 8/spl middot/10/sup 19//cm/sup 3/ to 5/spl middot/10/sup 19//cm/sup 3/, an InP collector, and an InGaAs/InAlAs base-collector superlattice grade, with a total 217 nm collector depletion layer thickness. The low base sheet (580 /spl Omega/) and contact (<10 /spl Omega/-/spl mu/m/sup 2/) resistivities are in part responsible for the high f/sub max/ observed.

THz MMICs based on InP HBT Technology

An indium-phosphide (InP) double-heterojunction bipolar transistor (DHBT) based suite of terahertz monolithic integrated circuits (TMICs) fabricated using 256nm InP DHBT transistors and a multipurpose three metal layer interconnect system is reported. The InP DHBT MMIC process is well suited for TMICs due to its high bandwidth (fmax = 808 GHz) and high breakdown voltage (BVCBo = 4V) and integrated 10-µm thick layer of BCB dielectric supporting both low-loss THz microstrip lines for LNA, PA, and VCO tuning networks, and high-density thin-film interconnects for compact digital and analog blocks. TMIC low noise and driver amplifiers, fixed and voltage controlled oscillators, dynamic frequency dividers, and double-balanced Gilbert cell mixers have been designed and fabricated. These results demonstrate the capability of 256nm InP DHBT technology to enable sophisticated single-chip heterodyne receivers and exciters for operation at THz frequencies.

InP HBT Integrated Circuit Technology for Terahertz Frequencies

We report on the development of an InP DHBT integrated circuit technology for applications at the lower range of the THz frequency band (0.3-3 THz) 0.25um HBTs demonstrate an extrapolated fmax of >800GHz while maintaining a common-emitter breakdown voltage of >4V. The transistors have been integrated a full IC process that includes three-levels of interconnects, backside wafer thinning to 50um with a through-wafer via process, and a backside etch singulation process that allows for the formation of free standing integrated waveguide probes. The technology has been utilized to demonstrate amplifiers, oscillators and dynamic frequency dividers all operating at >300GHz.

InP HBT amplifier MMICs operating to 0.67 THz

Two indium-phosphide (InP) double-heterojunction bipolar transistor (DHBT) based terahertz monolithic integrated circuit (TMIC) amplifiers are reported with record operating bandwidths up to 694 GHz. The first amplifier uses 3 μm long emitter transistors, has 24 dB gain at 670 GHz, and a saturated output power of -4 dBm at 585 GHz. The second amplifier uses 6 μm long emitter transistors, has 20 dB gain at 655 GHz, and a saturated output power of -0.7 dBm at 585 GHz. Both TMICs use Teledynes 130nm InP DHBT transistors in a common base configuration and are matched using inverted CPW transmission lines realized using a three-metal-layer high-density thin-film interconnects system. These results demonstrate the capability of 130nm InP DHBT technology to enable sophisticated TMIC circuits for operation in the terahertz band.

Transistor and circuit design for 100-200 GHz ICs

Compared to SiGe, InP HBTs offer superior electron transport properties but inferior scaling and parasitic reduction. Figures of merit for mixed-signal ICs are developed and HBT scaling laws introduced. Device and circuit results are summarized, including a simultaneous 450 GHz f/sub /spl tau// and 490 GHz f/sub max/ DHBT, 172-GHz amplifiers with 8.3-dBm output power and 4.5-dB associated power gain, and 150-GHz static frequency dividers (a digital circuit figure-of-merit for a device technology). To compete with advanced 100-nm SiGe processes, InP HBTs must be similarly scaled and high process yields are imperative. Described are several process modules in development: these include an emitter-base dielectric sidewall spacer for increased yield, a collector pedestal implant for reduced extrinsic C/sub cb/, and emitter junction regrowth for reduced base and emitter resistances.