9.5-14.5 GHz GaAs HBT 1W MMIC with 55% peak power added efficiency

A fully matched, broadband, high efficiency MMIC power amplifier using AlGaAs/GaAs HBTs has been designed and tested. At 7 V collector bias, this HBT amplifier produced 31 dBm CW peak output power with 9 dB gain and 55% peak power-added efficiency in the 9.5-14.5 GHz band. To the authors' knowledge, this is the highest efficiency ever achieved from a broadband MMIC power amplifier     

A 40-GHz D-type flip-flop using AlGaAs/GaAs HBT's

We report master-slave D-type flip-flop (D-FF) circuit implemented with AlGaAs/GaAs HBT's. The fabricated HBT's had an f_T of 107 GHz and an f_max of 110 GHz. To maximize the speed, the logic swing and transistor size in the IC were optimized. In the D-FF, to facilitate the high-speed testing, a selector circuit was integrated on the same chip. As a result, the operation of this IC was confirmed up to 40 GHz, which is the highest speed in D-FF     

Fully-planar AlGaAs/GaAs HBT's achieved by selective CBE regrowth

This paper describes a novel fully planar AlGaAs/GaAs heterojunction bipolar transistor (HBT) technology using selective chemical beam epitaxy (CBE). Planarization is achieved by a selective regrowth of the base and collector contact layers. This process allows the simultaneous metallization of the emitter, base and collector on top of the device. For the devices with an emitter-base junction area of 2×6 μm² and a base-collector junction area of 14×6 μm², a current gain cut off frequency of 50 GHz and a maximum oscillation frequency of 30 GHz are achieved. The common emitter current gain h_FE is 25 for a collector current density J_c of 2×10⁴ A/cm²     

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 HBT's with base sheet resistances between 100 and 350 Ω/□. In this work, we investigate five series of AlGaAs/GaAs HBT growths in which the base thickness was varied between 500 and 1600 Å and the base doping level between 2.9× and 4.7×10¹⁹ cm^-3. The dc current gain of large area devices (L=75 μm×75 μm) 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/cm² ) at a base sheet resistance of 330 Ω/□. A high dc current gain of 220 (@ 10 kA/cm²) was also confirmed in small area devices (L=8 μm×8 μm). 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_t ~68 GHz and f_max~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     

High-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's with p/sup +//p regrown base contacts

The present paper describes a new approach to fabricating high performance HBT's with low base resistance. Their base contact resistance is reduced by using MOMBE selective growth in the extrinsic base region-a key process in the fabrication of high-f/sub max/ AlGaAs/InGaAs and AlGaAs/GaAs HBT's. A p/sup +//p regrown base structure, which consists of a 40-nm-thick graded InGaAs strained layer and a heavily C-doped regrown contact layer, is used for the AlGaAs/InGaAs HBT's to reduce both their base transit time and base resistance, while preventing aluminum oxide incorporation at the regrowth interface. An h/sub fe/ of 93, an f/sub T/ of 102 GHz, and an f/sub max/ of 224 GHz are achieved for a 1.6-/spl mu/m/spl times/4.6-/spl mu/m HBT, together with reduced base push-out effects and improved reliability. AlGaAs/GaAs HBT's with an 80-nm-thick uniform base layer that have high f/sub max/ values ranging from 140-216 GHz are also fabricated using the selective growth technique. These results confirm the high potential of the proposed HBT's, especially for microwave and millimeter-wave applications.<>     

A new self-alignment technology using bridged base electrode forsmall-scaled AlGaAs/GaAs HBT's

The fabrication and characterization of a new self-aligned HBT utilizing bridged base-electrode technology (BBT) are presented. This new technology simplifies the fabrication process and relaxes the limitations in device size scaling, thus decreasing the emitter size to 1 μm×1 μm. In spite of a large junction periphery area ratio, a good current gain of more than 10 is obtained in an HBT with an emitter size of 1 μm×1 μm. A series of fabricated HBTs shows excellent high-speed performance. The highest values of f_T =90 GHz and f_max=63 GHz are obtained in an HBT with an emitter size of 1 μm×5 μm. The realization of HBTs with small emitters and excellent high-frequency characteristics demonstrates the effectiveness of this new technology     

Stress current behavior of InAlAs/InGaAs and AlGaAs/GaAs HBT's withpolyimide passivation

InAlAs/InGaAs and AlGaAs/GaAs HBTs, with heavily Be-doped base layers, have been fabricated and their reliability under excessive forward current tested. To understand the HBT material difference, a common process based on a polyimide planarization method is applied to the fabrication. While short-term degradation induced by stress current is observed for AlGaAs/GaAs HBTs, InAlAs/InGaAs HBTs are stable up to a current density of 1.5×10⁵ A/cm², indicating the absence of substantial Be diffusion. An analysis of base current has shown a striking contrast between the HBTs in terms of the stressing effect on the surface recombination along emitter junction periphery     

Large signal modelling of GaAs/AlGaAs HBT's with separation of the surface recombination current

The effects of surface recombination on an AlGaAs/GaAs HBT have been investigated. Studies of Gummel-plots for devices with different sized base emitter junctions made it possible to separate the surface recombination from the bulk current. An extension of the Gummel–Poon model that includes this surface recombination current is suggested. The large-signal performance was evaluated by two methods, power spectrum characteristics and by design and characterization of a power amplifier. For these two measurement set-ups, measured data was compared with simulations of the model both including and excluding the surface recombination current. It is clearly seen that without including the surface recombination current, it is impossible to correctly represent the large-signal performance. The model is also verified with DC characteristics and S-parameters.     

Analysis of carrier-blocking effect in AlGaAs/GaAs HBT's withinsulating external collector and design criteria for collector-up HBT's

Two-dimensional simulations of cutoff frequencies for AlGaAs/GaAs HBT's with perfectly insulating external collector are made, and the results are compared with those for a case with semi-insulating external collector and for a case with normal n^- external collector. It is found that in the case with perfectly insulating external collector, minority carriers injected into the base from the emitter are partially blocked by the insulating layer and accumulate in the external base region. These carriers increase the effective base delay time, resulting in remarkable degradation of the cutoff frequency. In relation to this effect, a collector-up HBT is also simulated, and the design criteria for it are discussed. It is concluded that the effective emitter width should be made narrower than the collector width     

Electron quasi-Fermi level-Fermi level splitting at thebase-emitter junction of AlGaAs/GaAs HBT's

The amount of electron quasi-Fermi level splitting in the emitter-base junction of AlGaAs/GaAs single- and double-heterojunction bipolar transistors is computed. The degree of splitting is found to be generally small, and less pronounced in double-heterojunction devices. However, it is argued that the effect of the splitting on the current gain may be significant     

Large-signal microwave characterization of AlGaAs/GaAs HBT's basedon a physics-based electrothermal model

A physics-based multicell electrothermal equivalent circuit model is described that is applied to the large-signal microwave characterization of AlGaAs/GaAs HBT's. This highly efficient model, which incorporates a new multifinger electrothermal model, has been used to perform dc, small-signal and load-pull characterization, and investigate parameter-spreads due to fabrication process variations. An enhanced Newton algorithm is presented for solving the nonlinear system of equations for the model and associated circuit simulator, which allows a faster and more robust solution than contemporary quasi-Newton nonlinear schemes. The model has been applied to the characterization of heterojunction bipolar transistor (HBT) microwave power amplifiers     

Electron velocity overshoot in the collector depletion layer of AlGaAs/GaAs HBT's

Electron velocity in the collector depletion layer of AlGaAs/ GaAs heterojunction bipolar transistors (HBT's) is characterized by analyzing the cutoff frequencies. The ftvalue of tested HBT's was 40 GHz at a collector voltage VCEof 2 V, and it significantly decreased to 27 GHz at VCE= 5 V. A conventional model assuming a constant electron velocity in the collector depletion region does not account for this ftvariation. A new simple model composed of a velocity overshoot region and a saturation velocity region is proposed and it successfully explains the variation.     

AlGaAs/GaAs Heterojunction bipolar power transistors

An AlGaAs/GaAs heterojunction bipolar transistor with a total emitter periphery of 320 ?m has been developed for power amplifier applications. For the base contact, Zn diffusion was used to convert the n-type emitter material into p-type with a doping of ?1.0 × 1020 cm?3. Because of the highly doped layer, contact resistivity was extremely low (5 × 10?7 ?cm2). At 3 GHz, a CW output power of 320 mW with 7 dB gain and 30% power-added efficiency was obtained. Under pulsed operation, the output power increased to 500 mW with 6 dB gain and 40% power-added efficiency. With further device structure optimisations, the power performance of heterojunction bipolar transistors is expected to rival, or even surpass, that of the GaAs MESFETs.     

Ku波段12 W GaAs pHMET功率MMIC

报道了一款采用0.25μm GaAs功率MMIC工艺研制的Ku波段功率放大器芯片。芯片采用三级放大拓扑结构,末级输出匹配电路按照高效率设计,同时优化前后级推动比控制前级电流。级间采用有耗匹配电路设计,提高大信号状态下的稳定性。在16~18GHz频带范围内漏压8.5V、脉宽1μs、占空比40%的工作条件下线性增益大于25dB;饱和输出功率大于12 W,饱和效率大于32%,功率增益大于21dB,功率增益平坦度小于±0.5dB。芯片尺寸为3.5mm×4.6mm。     

High-performance AlGaAs/GaAs HBT's utilizing proton-implanted buried layers and highly doped base layers

Fabrication of AlGaAs/GaAs heterojunction bipolar transistors (HBT's) using a proton-implanted external collector layer and a highly doped base layer is presented. Influence of the proton implantation on base-collector junction characteristics is systematically investigated. At the optimized implantation condition, a buried semi-insulating layer beneath the external base is formed without deteriorating the junction current-voltage characteristics. In a fabricated HBT with 2 µm × 10 µm emitter size, a cutoff frequency fTof 50 GHz and a maximum oscillation frequency fmaxof 70 GHz have been achieved.     

Emitter size effect on current gain in fully self-alignedAlGaAs/GaAs HBT's with AlGaAs surface passivation layer

The emitter size effect for fully self-aligned AlGaAs-GaAs heterojunction bipolar transistors (HBTs) with depleted AlGaAs passivation layers, in which the partially thinned AlGaAs emitter is self-aligned by using the dual sidewall process, is investigated. It is demonstrated that drastic improvement in the emitter size effect can be achieved with an AlGaAs passivation layer as small as 0.2 μm in width, due to the surface recombination current reduction by a factor of 1/40 in the extrinsic base region. It has also been found that the base current is dominated by excess leakage current in the proton-implanted isolation region     

AlGaAs/InGaAs/GaAs quantum-well power MISFET at millimeter-wavefrequencies

An AlGaAs/InGaAs/GaAs quantum-well MISFET developed for power operation at millimeter-wave frequencies is described. The InGaAs channel is heavily doped to increase the sheet carrier density, resulting in a maximum current density of 700 mA/mm with a transconductance of 480 mS/mm. The 0.25-μm×50-μm device delivers a power density of 0.76 W/mm with 3.6-dB gain and 19% power-added efficiency at 60 GHz. At 5.2 dB gain, the power density is 0.55 W/mm. A similar device built on an undoped InGaAs channel had much poorer power performance and no speed advantage     

Failure mechanisms in AlGaAs/GaAs power heterojunction bipolartransistors

We report the failure mechanisms resulting in the second breakdown characteristics found in AlGaAs/GaAs power heterojunction bipolar transistors (HBTs). The dominant failure mechanism is identified to be the increasingly larger base-collector leakage current at elevated junction temperatures. This failure mechanism is compared with those found in silicon bipolar transistors     

High-performance GaAs power MESFET with AlGaAs buffer layer

The performance of a power MESFET has been significantly improved by using an AlGaAs heterobuffer. The conduction-band discontinuity at the heterointerface acts as a potential barrier for electron confinement; the RF conversion efficiency and power gain of the FET were very high compared with a standard MESFET. We have achieved 41% power-added efficiency with 0.88 W/mm power density at 21.5 GHz and 30% efficiency with 0.56 W/mm at 35 GHz.     

500 mA AlGaAs/GaAs power heterojunction bipolar transistor

The current-voltage characteristics of 500 mA AlGaAs/GaAs power heterojunction bipolar transistors are reported and the influence of case temperature on current handling capability and current gain are analysed. Current handling capabilities of 400-800 mA/mm per emitter periphery at different case temperatures have been successfully demonstrated using a low-doped GaAs layer as an emitter ballasting resistor to obtain a uniform current distribution over individual emitter fingers. A current gain of 50 at a collector current of 500 mA was realised at room temperature for three elementary devices bonded in parallel, each device comprised ten (5*25 mu m/sup 2/) emitter fingers.<>