R.L. Pierson

High-power 10-GHz operation of AlGaN HFET's on insulating SiC

We report the first high-power RF characterization of AlGaN HFETs fabricated on electrically insulating SiC substrates. A record total power of 2.3 W at 10 GHz was measured from a 1280-/spl mu/m wide HFET at V/sub ds/=33 V. An excellent RF power density of 2.8 W/mm was measured on a 320-/spl mu/m wide HFET. These values are a result of the high thermal conductivity of SiC, relative to the typical substrate, sapphire.

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.

A 6-b, 4 GSa/s GaAs HBT ADC

A GaAs-AlGaAs heterojunction bipolar transistor (HBT) process was developed to meet the speed, gain, and yield requirements for analog-to-digital converters (ADCs). The HBT has current gain of over 100 and f/sub T/ and f/sub MAX/ of over 50 GHz. A 6-b, 4 GSa/s (4 giga-samples/s) ADC was designed and fabricated in this process. The ADC uses an analog folding architecture, includes an on-chip master-slave track-and-hold (T/H) circuit, and provides Gray-encoded digital outputs. The ADC achieves 5.6 effective bits at 4 GSa/s, a faster clock rate than any noninterleaved semiconductor ADC reported to date. It has a resolution bandwidth (the frequency at which effective bits has dropped by 0.5 b) of 1.8 GHz at 4 GSa/s, higher than any published ADC. The chip operates at up to 6.5 GSa/s. GaAs HBT ICs are especially prone to high operating temperatures. This led to reliability problems that were overcome by the use of a fast DC thermal simulator written for this project. A SPICE model for self-heating effects is also described. >

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].

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.

Thermal design and simulation of bipolar integrated circuits

Keeping device operating temperatures within reasonable limits is necessary for reliability of all ICs and important for achieving the expected performance for many ICs. GaAs heterojunction bipolar transistors (HBTs) offer high speed and good device matching characteristics that are attractive for many high-speed circuits, but they are more susceptible than other IC technologies to the unexpected generation of very high junction temperatures. The reasons for this tendency are discussed, and an HBT sample-and-hold (S/H) circuit that had device temperature rises of over 300 degrees C is described. To address this problem, a new thermal simulation tool called ThCalc was created. ThCalc calculates the temperature profile of an IC and runs fast enough to allow calculations on a whole chip. ThCalc was used to redesign the S/H IC to reduce the largest temperature rise by a factor of 2.7 with a minimal impact on circuit size. >

A high-speed, low-power divide-by-4 frequency divider implemented with AlInAs/GaInAs HBT's

The authors describe the first frequency divider demonstrated using AlInAs/GaInAs heterojunction bipolar transistors (HBTs). The divider (a static 1/4 divider circuit) operates up to a maximum frequency of 17.1 GHz, corresponding to a gate delay of 29 ps for a bilevel current-mode logic (CML) gate with a fan-out of 2, and a total power consumption of 67 mW (about 4.5 mW per equivalent NOR gate). These results demonstrate the potential of AlInAs/GaInAs HBTs for implementing low-power, high-speed integrated circuits.<<ETX>>

High-performance MOCVD-grown AlGaAs/GaAs heterojunction bipolar transistors with carbon-doped base

Excellent microwave performance is demonstrated by metalorganic chemical vapor deposition (MOCVD) grown AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with carbon-doped base. These devices achieve a current-gain cutoff frequency of 76 GHz and a maximum frequency of oscillation of 102 GHz. Varying the device structures allows the current gain to reach over 300 in structures with a base doping of 2*10/sup 19 /cm/sup -3/. A static divide-by-four divider implemented with C-doped base HBTs has been operated up to a frequency of 20.4 GHz. These results indicate the suitability of carbon doping for high-performance HBTs.<<ETX>>

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.

AlGaAs/GaAs HBT IC's for high-speed lightwave transmission systems

The implementation of multigigabit-per-second optical communication systems requires many high-speed electronic circuit components that meet stringent performance requirements. Several important research prototype circuits for fiber-optic transmission, implemented in a baseline AlGaAs/GaAs HBT process, are discussed. These include a 20 Gb/s decision circuit, a 27 Gb/s 1:2 demultiplexer, a 30 GB/s 2:1 multiplexer, a 27 Gb/s 4:1 multiplexer, and a 11 Gb/s laser driver IC. >