AlGaAs/GaAs HBT的设计研究

利用BIPOLE计算机程序,评价了具有不同版图、不同掺杂分布和不同层厚的AlGaAs/GaAs HBT的频率性能,研究了HBT的最佳化设计,并比较了HBT和多晶硅发射极晶体管的大电流性能。研究表明,对发射极条宽S_E<3μm的HBT来说,在电流密度小于1×10~5A/cm~2时,并未发现电流集聚效应,由最高f_T确定的HBT电流处理容量要比多晶硅发射极晶体管的大两倍多。对基区掺杂为1×10~(19)cm~(-3)的典型工艺n-p-n型AlGaAs/GaAs HBT,已获得了一个最佳化的最高振荡频率f_(mos(?))的方程式:f_(mosc)=337(W_(Bop)/S_E)~(1/2)GHz,式中,W_(Bop)是最佳基区宽度,S_E是发射极条宽,二者都以微米为单位。     

Breakdown behavior of GaAs/AlGaAs HBTs

Avalanche breakdown behavior at the collector junction of the GaAs/AlGaAs HBT (heterojunction bipolar transistor) has been studied. Junction breakdown characteristics displaying hard breakdown, soft breakdown, and negative resistance breakdown behavior were observed and are interpreted by analysis of localized microplasma effects, uniform microplasma-free behavior, and associated current gain measurements. Light emission from the collector-base junction of the GaAs/AlGaAs HBT was observed and used to investigate breakdown uniformity. Using a simple punchthrough breakdown model, the theoretical breakdown curves at different collector doping concentrations and thicknesses were computed and found to be in agreement with maximum breakdown voltages measured from devices displaying the most uniform junction breakdown. The serious current gain degradation of GaAs/AlGaAs HBTs at low current densities was analyzed in connection with the measurement of a large collector-emitter breakdown voltage. The unexpected functional relationship between the collector-emitter breakdown voltage and collector-base breakdown voltage is explained by the absence of a hole-feedback effect for devices not exhibiting transistor action     

Submicron-square emitter AlGaAs/GaAs HBTs with AlGaAshetero-guardring

Successful operation of submicron-square emitter AlGaAs/GaAs HBTs is demonstrated for the first time by using a fully mesa-structure-type emitter-base junction-area definition method with an AlGaAs hetero-guardring. The hetero-guardring reduces surface recombination current at the emitter-mesa edge to 1.4 μA/μm. This is 1/10 of that for devices without the guardring. Here, dc gains of 20, 26, and 40 are achieved for 0.5 μm×0.5 μm, 0.7 μm×0.7 μm, and 0.9 μm×0.9 μm emitter HBTs, respectively. An f_T of 40 GHz, and an f_max of 30 GHz are obtained for 0.9 μm×0.9 μm at a J_C of 1.0×10⁵ A/cm²     

MBE-grown AlGaAs/GaAs HBTs on InP substrate

AlGaAs/GaAs HBTs are fabricated on InP substrates for the first time. Preliminary results show a current gain of 5 at a collector current density of 2 × 104A/cm2 in spite of a dislocation density higher than 109/cm2.     

Millimetre wave performance of carbon-doped-base AlGaAs/GaAs HBTs

AlGaAs/GaAs HBTs with f/sub T/ of 52 GHz and f/sub max/ of 85 GHz have been obtained using a heavily-carbon-doped base layer. The HBT epitaxial layers were prepared by low-pressure MOVPE using carbon tetrachloride as the carbon source. To the author's knowledge, this work reports the first carbon-doped AlGaAs/GaAs HBTs with f/sub T/ and f/sub max/ greater than 50 GHz.<>     

Reliability characteristics of ohmic contacts for AlGaAs/GaAs HBTs

The thermal stability of ohmic contacts for AlGaAs/GaAs HBTs is presented. Ti/Pt/Au, Ti/Pt/Au and Cr/Pt/Au, and AuGe/Ni/Ti/Pt/Au were investigated for emitter, base, and collector contacts, respectively. As a result of 200 degrees C storage tests, it was found that these contacts did not limit the reliability of AlGaAs/GaAs HBTs.<>     

Application of AlGaAs/GaAs HBTs for wideband direct-coupled amplifiers

An AlGaAs/GaAs HBT direct-coupled amplifier has been designed and its characteristics described for the first time. The amplifier consists of two HBTs and three resistors without level-shift diodes. A superior amplifier performance of 11 dB gain with a 4 GHz bandwidth was obtained.     

Pulsed current stress of Berillium doped AlGaAs/GaAs HBTs

The major concern for reliability of Berillium doped HBTs is the diffusion of the base dopant towards the emitter. This degradation can be enhanced by the device self-heating and/or by REID mechanism. In order to separate the thermal and REID components to the Berillium outdiffusion we performed a pulsed current stress on AlGaAs/GaAs HBTs. In this paper we report on results obtained with different values of the duty cycles for this current.     

Degradation of AlGaAs/GaAs HBTs induced by hot carriers

In AlGaAs/GaAs HBTs, the instability of the surface states of the extrinsic base, which is revealed by mesa-etching and passivated by Si₃N₄, affects reliability. In this study the reverse constant current stress in an avalanche regime is applied across the emitter–base junction in order to test the stability of the heterojunction and the surface state of the extrinsic base. It has been identified that the surface of the extrinsic base is vulnerable to hot carriers. A new degradation mechanism is suggested and verified by numerical simulation. In addition, a way to improve the reliability is proposed based on the experimental results.     

28 Gbit/s selector IC using AlGaAs/GaAs HBTs

An ultra-high-speed selector IC has been developed for future optical transmission systems. The IC was fabricated with AlGaAs/GaAs HBT technology, for which the f/sub T/ is about 70 GHz. It operates at 28 Gbit/s with an output voltage swing of 1 V/sub p-p/. This is the fastest operating speed ever reported for a selector IC using any technology.<>     

AlGaAs/GaAs P-n-p HBTs with high maximum frequency of oscillation

An investigation of P-n-p HBTs (heterojunction bipolar transistors) with an f_max of 39 GHz and an f_t of 19 GHz is presented. Power-added efficiency of 31% was obtained in an amplifier at 10 GHz. The design of the high-speed AlGaAs/GaAs P-n-p HBTs takes account of the large degeneracy in the heavily n-type GaAs base. This doping-dependent degeneracy can induce gradients in the valence-band edge to improve the base transit time. High injection efficiency can be maintained in spite of the large degeneracy by increasing the aluminum content of the emitter. HBTs with emitter aluminum contents of 40% and 75% are described     

20-GHz 5-dB-gain analog multipliers with AlGaAs/GaAs HBTs

From-DC-to-above-20-GHz monolithic Gilbert cell analog multipliers have been developed using AlGaAs/GaAs HBT technology. As a double balanced active mixer, it exhibits very high conversion gain of above +5 dB with extremely high LO-IF isolation of 33 dB for RF/LO inputs up to 20 GHz. It exhibits conversion gain of +9 dB for 5 GHz RF/LO inputs. As a double balanced upconverter, it exhibits positive conversion gain with high LO-RF isolation of 23 dB for RF output up to 8.5 GHz. As a detection mixer in coherent optical heterodyne receivers, it can operate for RF/LO inputs up to 15 GHz under a less than -7.5 dBm LO input condition     

Integrated npn/pnp GaAs/AlGaAs HBTs grown by selective MBE

npn and pnp GaAs/AlGaAs heterojunction bipolar transistors have been successfully fabricated on the same GaAs substrate using selective molecular beam epitaxy and a new merged HBT processing technology. The DC and microwave characteristics of the transistors are equivalent to those of similar HBTs grown by conventional MBE on separate GaAs substrates.<>     

22 GHz 1/4 frequency divider using AlGaAs/GaAs HBTs

A divide-by-four frequency divider using AIGaAs/GaAs HBTs with GalnAs/GaAs emitter cap layers was designed and fabricated. A maximum toggle frequency of 22.15 GHz was obtained at a power supply voltage of 9 V and a total power dissipation of 712 mW. The minimum input signal power was under 0dBm and the free-running frequency was as high as 20 GHz.     

DC Characteristics of AlGaAs/GaAs/GaN HBTs Formed by Direct Wafer Fusion

We have fabricated AlGaAs/GaAs/GaN heterojunction bipolar transistors (HBTs) formed by direct wafer fusion with different fusion temperatures. By employing a low wafer fusion temperature of 550 degC, current gains as high as ~9 and output currents as high as ~65 mA (emitter size of 100times120 mum²) were obtained. The effective minority carrier lifetime in the base was estimated to have decreased ~20 times due to the fusion process. In comparison, HBTs produced with higher wafer fusion temperatures (600 degC and 650 degC) exhibit lower current gains (~2-3) and higher base-collector leakage currents     

采用AlGaAs/GaAs HBT制作的34.8GHz 1/4静态分频器

采用AlGaAs/GaAs异质结双极晶体管(HBT)设计的1/4静态分频器,在偏置条件下工作,可给出最大的截止频率f_T和最大的振荡频率f_(max)。应用于分频器中的f_T及f_(max)分别是68GHz和56GHz。试验结果是在9V电源和495mW功耗下,电路工作到34.8GHz。最小输入信号功率电平为0dBm。     

Equivalent circuit and ECL ring oscillators of graded-bandgap base GaAs/AlGaAs HBTs

Equivalent circuit parameters of graded-bandgap base GaAs/AlGaAs heterojunction bipolar transistors are derived by analysing static and microwave characteristics. Here, the estimated base transit time of 1.4 ps indicates that the average electron velocity is enhanced under the built-in field of the graded base. Additionally, ECL ring oscillators are simulated using the obtained parameters. The simulated propagation delay time of ECL gates agrees well with an experimental result of as short as 65 ps/gate.     

Growth and metallization of AlGaAs/GaAs carbon-doped HBTs usingtrimethylamine alane by CBE

It is shown that the entire structure of high-quality AlGaAs/GaAs heterojunction bipolar transistors (HBTs) including a nonalloyed δ-doped ohmic contact and in-situ Al metallization can be grown by chemical beam epitaxy (CBE) using a new precursor, trimethylamine alane, as the Al source. The graded Al_xGa_1-xAs and uniform GaAs bases (both ~1000 A thick) are doped with carbon to high 10 ¹⁹ cm^-3 using trimethyl-Ga. A current gain of 10 at a current density of 2500 A/cm² is obtained for both uniform- and graded-base HBTs. Both devices show good output characteristics     

High-linearity and small-chip AlGaAs/GaAs power HBTs for L-bandpersonal digital cellular applications

A high-linearity AlGaAs/GaAs power heterojunction bipolar transistor (HBT) is developed for personal digital cellular phones. For compact chip layout, thermal design was considered. To improve power performance, proton implantation, optimum alloy condition for collector electrodes, and multiple via holes were used. A 2400-μm²-emitter-area HBT fabricated on a 0.5×0.67 mm² substrate exhibits adjacent channel leakage powers below -53 dBc for 0.95- and 1.5-GHz π/4-shifted QPSK modulated input signals at a low collector-emitter voltage of 3.4 V. The HBT produces a 31.7-dBm output power, 50% power-added efficiency, and 15-dB linear power gain at 0.95 GHz, and produced a 31.3-dBm output power, 52% power-added efficiency, and 11.5-dB linear power gain at 1.5 GHz. These results were achieved on about one-fifth of the substrate area of conventional GaAs FETs