P.J. Zampardi

Current status and future trends of SiGe BiCMOS technology

The silicon germanium (SiGe) heterojunction bipolar transistor (HBT) marketplace covers a wide range of products and product requirements, particularly when combined with CMOS in a BiCMOS technology. A new base integration approach is presented which decouples the structural and thermal features of the HBT from the CMOS. The trend is to use this approach for future SiGe technologies for easier migration to advanced CMOS technology generations. Lateral and vertical scaling are used to achieve smaller and faster SiGe HBT devices with greatly increased current densities. Improving both the f/sub T/ and f/sub MAX/ will be a significant challenge as the collector and base dopant concentrations are increased. The increasing current densities of the SiGe HBT will put more emphasis on interconnects as a key factor in limiting transistor layout. Capacitors and inductors are two very important passives that must improve with each generation. The trend toward increasing capacitance in polysilicon-insulator-silicon (MOSCAP), polysilicon-insulator-polysilicon (Poly-Poly), and metal-insulator-metal (MIM) capacitors is discussed. The trend in VLSI interconnections toward thinner interlevel dielectrics and metallization layers is counter to the requirements of high Q inductors, potentially requiring a custom last metallization layer.

Role of neutral base recombination in high gain AlGaAs/GaAs HBT's

Neutral base recombination is a limiting factor controlling the maximum gain of AlGaAs/GaAs HBTs with base sheet resistances between 100 and 350 /spl Omega///spl square/. In this work, we investigate five series of AlGaAs/GaAs HBT growths in which the base thickness was varied between 500 and 1600 /spl Aring/ and the base doping level between 2.9/spl times/ and 4.7/spl times/10/sup 19/ cm/sup -3/. The dc current gain of large area devices (L=75 /spl mu/m/spl times/75 /spl mu/m) varies by as much as a factor of two at high injection levels for a fixed base sheet resistance, depending on the growth optimization. One of these series (Series TA) has the highest current gains ever reported in this base sheet resistance range, with dc current gains over 225 (@ 200 A/cm/sup 2/) at a base sheet resistance of 330 /spl Omega///spl square/. A high dc current gain of 220 (@ 10 kA/cm/sup 2/) was also confirmed in small area devices (L=8 /spl mu/m/spl times/8 /spl mu/m). High-frequency tests on a separate set of wafers grown under the same conditions indicate these high current gains can be achieved without compromising the RF characteristics: Both high and normal gain devices exhibit an f/sub t//spl sim/68 GHz and f/sub max//spl sim/100 GHz. By fitting the base current as a sum of two components, one due to recombination in the neutral base and the other in the space charge region, we conclude that an improvement in the minority carrier lifetime is responsible for the observed increase in dc current gain. Moreover, we observe a thickness-dependent variation in the effective minority carrier lifetime as the gains increase, along with a nonlinear dependence of current gain on base doping. Both phenomena are discussed in terms of an increase in Auger and radiative recombination relative to Hall-Shockley-Read recombination in optimized samples.

GaInP/GaAs HBTs for high-speed integrated circuit applications

The use of GaInP/GaAs heterojunction bipolar transistors (HBTs) for integrated circuit applications is demonstrated. The discrete devices fabricated showed excellent DC characteristics with low V/sub ce/ offset voltage and very low temperature sensitivity of the current gain. For a non-self-aligned device with a 3- mu m*1.4- mu m emitter area, f/sub T/ was extrapolated to 45 GHz and f/sub max/ was extrapolated to 70 GHz. The measured 1/f noise level was 20 dB better than that of AlGaAs HBTs and comparable to that of low-noise silicon bipolar junction transistors, and the noise bump (Lorentzian component) was not observed. The fabricated gain block circuits showed 8.5 dB gain with a 3-dB bandwidth of 12 GHz, and static frequency dividers (divide by 4) were operable up to 8 GHz.<<ETX>>

A GaAs BiFET LSI technology

A GaAs BiFET LSI technology has been successfully developed for low power, mixed mode communication circuit applications. The direct placement of the FET on the HBT emitter cap layer simplifies the device epitaxial growth and process integration. High integration levels and functional circuit yield have been achieved. Excellent HBT and FET characteristics have been produced with the noise figure of the FETs comparable to those of traditional MESFETs, enabling them to perform well in front end receiver applications. Through this technology, several LSI circuits, including 32-bit by 2-bit shift registers and a single-chip DRFM have been successfully demonstrated.

HBT devices and circuits for signal and data processing

Abstract Production and laboratory AlGaAs/GaAs HBT processes were developed, enabling implementation of high-precision and high-speed circuits to meet the ever increasing demands on information bandwidths. Under normal bias conditions, the production HBT process shows transistor f t and f max above 50 GHz, while the laboratory process reveals f t of 60 GHz and f max of 110 GHz. With these two HBT processes, numerous high-speed and high-precision circuits for signal and data processing were implemented. In particular, we have designed and fabricated a 8-bit, 2 GS s −1 ADC and a 6-bit, 4 GS s −1 ADC for instrumentation and digital receiver applications; a 40 GBit s −1 4:1 multiplexer and an 8-channel, 2.5 GBit s −1 laser driver array for optical communication transmitters; a 50 dBΩ, 25 GHz preamplifier, a DC-26 GHz 10–16 dB variable gain amplifer, a 30 GBit s −1 data/clock regeneration circuit, two 40 GBit s −1 nonlinear (differentiate/rectify and delay/multiply) clock regeneration circuits, and a 40 GBit s −1 phase detector circuit for optical communication receivers.

Demonstration of low-knee voltage high-breakdown GaInP double HBTs using novel compound collector design

We have demonstrated a heterojunction bipolar transistor using a novel compound collector (CCHBT) design that allows a low-knee voltage and high-breakdown voltage to be obtained simultaneously. The novel aspect of this design is to use a short wide band-gap collector only over a narrow portion of the collector, where the field is highest. This allows support of high fields while maintaining a low overall collector resistance due to the higher mobility of the narrow band-gap material. We demonstrate an offset voltage reduction of about 35% and a knee-voltage reduction of 30%, while increasing both BVCEO and BVCBO by 20 and 27%, respectively, compared to a single heterojunction device of the same collector length.

High performance Al/sub 0.35/Ga/sub 0.65/As/GaAs HBT's

AlGaAs emitter heterojunction bipolar transistors (HBTs) are demonstrated to have excellent dc and RF properties comparable to InGaP/GaAs HBTs by increasing the Al composition. Al/sub 0.35/Ga/sub 0.65/As/GaAs HBTs exhibit very high dc current gain at all bias levels, exceeding 140 at 25 A/cm/sup 2/ and reaching a maximum of 210 at 26 kA/cm/sup 2/ (L=1.4 /spl mu/m/spl times/3 /spl mu/m, R/sub sb/=330 /spl Omega///spl square/). The temperature dependence of the peak dc current gain is also significantly improved by increasing the AlGaAs mole fraction of the emitter. Device analysis suggests that a larger emitter energy gap contributes to the improved device performance by both lowering space charge recombination and increasing the barrier to reverse hole injection.

Heterostructure-based high-speed/high-frequency electronic circuit applications

Abstract With the growth of wireless and lightwave technologies, heterostructure electronic devices are commodity items in the commercial marketplace [Browne J. Power-amplifier MMICs drive commercial circuits. Microwaves & RF, 1998. p. 116–24.]. In particular, HBTs are an attractive device for handset power amplifiers at 900 MHz and 1.9 GHz for CDMA applications [Lum E. GaAs technology rides the wireless wave. Proceedings of the 1997 GaAs IC Symposium, 1997. p. 11–13; “Rockwell Ramps Up”. Compound Semiconductor, May/June 1997.]. At higher frequencies, both HBTs and p-HEMTs are expected to dominate the marketplace. For high-speed lightwave circuit applications, heterostructure based products on the market for OC-48 (2.5 Gb/s) and OC-192 (10 Gb/s) are emerging [http://www.nb.rockwell.com/platforms/network_access/nahome.html#5.; http://www.nortel.com/technology/opto/receivers/ptav2.html.]. Chips that operate at 40 Gb/ have been demonstrated in a number of research laboratories [Zampardi PJ, Pierson RL, Runge K, Yu R, Beccue SM, Yu J, Wang KC. hybrid digital/microwave HBTs for >30 Gb/s optical communications. IEDM Technical Digest, 1995. p. 803–6; Swahn T, Lewin T, Mokhtari M, Tenhunen H, Walden R, Stanchina W. 40 Gb/s 3 Volt InP HBT ICs for a fiber optic demonstrator system. Proceedings of the 1996 GaAs IC Symposium, 1996. p. 125–8; Suzuki H, Watanabe K, Ishikawa K, Masuda H, Ouchi K, Tanoue T, Takeyari R. InP/InGaAs HBT ICs for 40 Gbit/s optical transmission systems. Proceedings of the 1997 GaAs IC Symposium, 1997. p. 215–8]. In addition to these two markets, another area where heterostructure devices are having significant impact is for data conversion [Walden RH. Analog-to digital convertor technology comparison. Proceedings of the 1994 GaAs IC Symposium, 1994. p. 217–9; Poulton K, Knudsen K, Corcoran J, Wang KC, Nubling RB, Chang M-CF, Asbeck PM, Huang RT. A 6-b, 4 GSa/s GaAs HBT ADC. IEEE J Solid-State Circuits 1995;30:1109–18; Nary K, Nubling R, Beccue S, Colleran W, Penney J, Wang KC. An 8-bit, 2 gigasample per second analog to digital converter. Proceedings of the 1995 GaAs IC Symposium, 1995. p. 303–6.]. In this paper, we will discuss the present and future trends of heterostructure device applications to these areas.

Hybrid digital/microwave HBTs for >30 Gb/s optical communications circuits

The demand for higher bit rate communications systems requires the development of key chip sets using high speed technologies such as AlGaAs/GaAs HBTs. However, many of these circuits place conflicting demands on the device characteristics. We present device and circuit results using a hybrid of our digital and microwave HBT processes. This process results in high yield, high performance devices and circuits and is flexible enough to easily incorporate various epitaxial structures required by different chips. It also provides access to Schottky diodes allowing ADCs and shock-line structures to be fabricated with these HBTs.

Circuit demonstrations in a GaAs BiFET technology

Abstract In this paper, wer present several circuits demonstrating the versatility of our GaAs BiFET technology. Among the circuits presented here are a 360 ps access time SRAM, a 2 GHz 2-bit single-chip DRFM, a reduced power laser driver at 1.5 GHz, and an OEIC suitable for 4 Gb/s systems. This technology will have a significant impact on many areas of circuit research such as delta-sigma analog to digital convertors and mixed-mode applications.