A high-current-gain low-temperature pseudo-heterojunction bipolartransistor utilizing sidewall base-contact structure (SICOS)

An experimental pseudo-heterojunction bipolar transistor (HBT) is described. The pseudo-HBT is a homojunction bipolar transistor having a moderately doped emitter and a heavily doped base, providing a bandgap profile similar to those of actual HBTs. Analyses including real constraints, such as a heavily doped emitter region for ohmic contact and the profile tail in the base region, show a significant change in the way they affect injection characteristics between 300 and 77 K. Based on these analyses, an impurity profile is carefully designed for upward mode operation. The electron injection into the external base region. which is thought to be unfavorable for high current gain in the upward mode, is avoided by using the sidewall base-contact structure. The fabricated transistor clearly displays a negative temperature dependence on current gain. The current gain is 107 at 77 K, which is 5 times higher than the room-temperature current gain. In addition, current gain excluding the nonideal effects at 77 K is as high as 25,000. These results not only remove gain degradation at low temperatures, but also verify the pseudo-HBT concept, in which an injection efficiency as high as that of an HBT can be obtained using only homojunctions. Based on these results, the small emitter transit time inherent in pseudo-HBTs is analyzed     

Base-emitter injection characterization in low-temperaturepseudo-heterojunction bipolar transistors

Carrier injection characteristics in a pseudo-heterojunction bipolar transistor (pseudo-HBT) are clarified both theoretically and experimentally. It is found that a low-concentration external-base structure completely rejects carrier injections and selectively injects electrons into the intrinsic base at low temperatures. This unique property inherent in low-temperature operation is verified in an experimental pseudo-HBT. Based on the results, the vertical and horizontal scaling rules for pseudo-HBTs are clarified. The analysis reveals that the low-temperature bipolar transistor has a very small emitter- and external-base charging time, which allows excellent vertical and horizontal scalability for superior to that of conventional room-temperature transistors     

Advanced process device technology for 0.3-μm high-performancebipolar LSIs

A new method is developed for forming shallow emitter/bases, collectors, and graft bases suitable for high-performance 0.3-μm bipolar LSIs. Fabricated 0.5-μm U-SICOS (U-groove isolated sidewall base contact structure) transistors are 44 μm², and they have an isolation width of 2.0 μm, a minimum emitter width of 0.2 μm, a maximum cutoff frequency (f_T) of 50 GHz, and a minimum ECL gate delay time of 27 ps. The key points for fabricating high-performance 0.3-μm bipolar LSIs are the control of the graft base depth and the control of the interfacial layer between emitter poly-Si and single-Si. The importance of a tradeoff relation between f_T and base resistance is also discussed     

多晶硅发射极晶体管的低温频率特性研究

本文考虑低温下半导体中载流子冻析效应和浅能级杂质的陷阱效应等因素,分析了多晶硅发射极晶体管的低温频率特性。研究表明,受载流子冻析效应的影响,基区电阻在低温下随温度下降接近于指数上升,使晶体管的频率性能变环;而由于浅能级杂质的陷阱效应,低温下基区和发射区渡越时间变长,截止频率下降。这些因素在低温器件设计中应予重视。     

Self-aligned AlGaAs/GaAs HBT with low emitter resistance utilizingInGaAs cap layer

A self-aligned AlGaAs/GaAs heterojunction bipolar transistor (HBT) with an InGaAs emitter cap layer that has very low emitter resistance is described. In this structure, a nonalloyed emitter contact allows the emitter and base electrodes to be formed simultaneously and in a self-aligned manner. The reduction of emitter resistance greatly improves the HBT's transconductance and cutoff frequency. In fabricated devices with emitter dimensions of 2 μm×5 μm, a transconductance-per-unit-area of 16 mS/μm² and a cutoff frequency of 80 GHz were achieved. To investigate high-speed performance, a 21-stage ECL ring oscillator was fabricated using these devices. Propagation delay times as low as 5.5 ps/gate were obtained, demonstrating the effectiveness of this structure     

High-speed InP-InGaAs heterojunction phototransistors employing anonalloyed electrode metal as a reflector

High-speed InP-InGaAs heterojunction phototransistors (HPT's) with a base terminal (three-terminal HPT's) have been fabricated. These HPT's have nonalloyed electrodes functioning as reflectors and a configuration in which light is incident through the substrate. These features lead to an increase in quantum efficiency in spite of the thin base and collector light-absorbing layers. Optical gain dependence on collector current is weak because of the low recombination current at the emitter-base interface. Maximum optical-gain cutoff frequencies of 22 and 14 GHz are obtained for a 3×3-μm² emitter HPT illuminated by 1.3- and 1.55-μm light, respectively. This HPT has the capability of operating as a high-speed heterojunction bipolar transistor (HBT) as well. A current-gain cutoff frequency (f_T) of 128 GHz is obtained for a 3×9-μm² emitter HBT fabricated on the same wafer. Equivalent circuit analysis, in which all the components are determined by measuring both the electrical and optical characteristics of a three-terminal HPT, shows good agreement with experimental results     

Modeling and characterization of SIPOS emitter and quasi-SISemitter bipolar transistors

SIPOS (semi-insulating polycrystalline Si) emitter bipolar transistors have been fabricated with a common-emitter current gain of 8000 and a figure of merit (gain divided by intrinsic base sheet resistance) of 200 (kΩ/sq)^-1. The high gain is attributed to a relatively low interface recombination velocity of the emitter contact, as measured by photo-induced microwave reflectometry. The cutoff frequency is measured to be 250 MHz, the low value attributed to a large emitter contact resistance of the SIPOS emitter. The authors suggest that a new figure of merit-transconductance divided by emitter resistance-should be considered for the comparison of the high-frequency performances of high emitter efficiency bipolar transistors. A quasi-SIS semiconductor-insulator-semiconductor emitter bipolar with a poly-Si emitter and undoped SIPOS as an interfacial layer was also fabricated. By incorporating a field-enhancement factor in the SIPOS, the behavior of this transistor is successfully explained by a SIS emitter model. The ideality factor ratio in the Gummel plot is attributed to the different barrier heights of electrons and holes at the SiO₂/n-Si interface     

On the operation configuration of SiGe HBTs based on power gain analysis

The power gain difference, under different device stability conditions, between common-emitter (CE) and common-base (CB) bipolar junction transistors (BJT) is analyzed comprehensively. The analysis reveals that the CB configuration offers higher maximum available power gain than the CE configuration in the device's high operation frequency range, while the inverse relation holds in the very low frequency range. In the intermediate frequency range, the base resistance value, mainly affected by the base doping concentration, determines which configuration offers higher maximum stable power gain (MSG). These analyses have explicit implications on the operation configurations of SiGe heterojunction bipolar transistors (HBTs). Employing a typical doping profile of Si bipolar junction transistors with a trapezoidal Ge profile in SiGe HBTs usually results in a larger base resistance than the emitter resistance. For these devices, the CE configuration exhibits higher MSG than the CB configuration. Employing a higher base doping concentration than the emitter with a box-type Ge profile considerably reduces the base resistance and thus favors the CB configuration for power amplification in this frequency range. The analysis are quantitatively verified with simulation and measurement results from SiGe HBTs of representative Ge and base doping profiles.     

A simulation study of high-speed silicon heteroemitter bipolartransistors

Using a two-dimensional numerical simulator, the upper limit of Si homotransistor cutoff frequency is estimated within the assumed conditions of punchthrough voltage. The potential speed advantages of silicon heteroemitter bipolar transistors (Si HBTs) (such as low emitter storage time, low emitter-base junction capacity, and possibility for large base width reduction) are shown by comparing Si HBTs with a Si homotransistor. It is confirmed that the cutoff frequency is enhanced from 48 to 127 GHz by the Si HBT structure. The optimum values of heteromaterial properties for high-speed HBT operation including energy gap, band discontinuity, and heterointerface recombination are discussed     

Current gain and transit-time effects in HBTs with graded emitterand base regions

Two-dimensional simulations of the combined effects of emitter and base grading on the current gain and cutoff frequency f_t of heterojunction bipolar transistor (HBT) devices are presented. At low bias, the highest current gain was found to be obtained with an abrupt emitter and reduced by base grading, with f_t proportional to the collector current. At high bias, current gain was found to be enhanced by emitter grading, while base grading was found to reduce current gain if without emitter grading. Anticipated grading effects of lower band spikes and base transit time are found to be greatly modified by the changes of carrier density, lifetime, diffusion potential, and series resistance with bandgap     

A new InGaP/GaAs tunneling heterostructure-emitter bipolar transistor (T-HEBT)

Excellent characteristics of an InGaP/GaAs tunneling heterostructure-emitter bipolar transistor (T-HEBT) are first demonstrated. The insertion of a thin n-GaAs emitter layer between tynneling confinement and base layers effectivelty eliminates the potential spike at base-emitter junction and reduces the collector-emitter offset voltage, while the thin InGaP tunneling confinement layer is employed to reduce the transporting time across emitter region for electrons and maintain the good confinement effect for holes. Experimentally, the studied T-HEBN exhibits a maximum current gain of 285, a relatively low offset voltage of 40 mW, and a current-gain cutoff frequency of 26.4 GHz.     

Ultra high-speed InP/InGaAs SHBTs with ft and fmax of 185 GHz

An InP/InGaAs single heterojunction bipolar transistor(SHBT) with high maximum oscillation frequency (f_(max)) and high cutoff frequency(f_t) is reported.Efforts have been made to maximize f_(max) and f_t simultaneously including optimizing the epitaxial structure,base-collector mesa over-etching and base surface preparation.The measured f_t and f_(max) both reached 185 GHz with an emitter size of 1×20μm~2,which is the highest f_(max) for SHBTs in mainland China.The device is suitable for ultra-high spee...     

Comparison of hot electron and related amplifiers

It is proposed that novel amplifiers be compared with each other and with existing amplifiers on the basis of as many figures of merit as are calculable. The bipolar transistor; field-effect transistor; Schottky-emitter, space-charge-limited-emitter, and tunnel-emitter, metal-base, hot-electron amplifiers are compared with respect to frequency cutoff and maximum frequency of oscillation. Using reasonable ground rules for the comparison, the amplifiers rank (with respect to frequency cutoff) in the order: Schottky emitter, bipolar transistor, space-charge-limited emitter, and tunnel emitter. With respect to maximum frequency, the amplifiers rank in the order: Schottky emitter; space-charge-limited emitter; tunnel emitter and bipolar transistor equivalent; and field-effect transistor.     

Fully Radiative Current Path Structure (FRACS) for sub-0.1 μmemitter transistor

A new structure is proposed for bipolar transistors - FRACS (Fully Radiative Current Path Structure). A FRACS transistor has a line emitter and a cylindrical base and collector or a point emitter and a spherical base and collector. Device parameters of the FRACS transistor is obtained by extending the conventional one-dimensional transistor model to a two- or three-dimensional model. In this structure, base transit time is reduced as the emitter size is reduced by radiative collector current flow. Using this model, a general bipolar transistor with a shallow link base is found to increase the cutoff frequency as the emitter size is reduced. The Kirk effect is suppressed in this structure because of the small collector current density at the collector-base junction. The effect was experimentally examined. A cylindrical base was fabricated by thermal diffusion of boron to achieve the FRACS transistor. Cutoff frequency was observed to increase as the emitter size was reduced. Maximum cut-off frequency of 64 GHz was achieved by this transistor with a 25-nm thick base formed by rapid vapor-phase diffusion     

75-GHz fT SiGe-base heterojunction bipolartransistors

The fabrication of silicon heterojunction bipolar transistors which have a record unity-current-gain cutoff frequency (f_T) of 75 GHz for a collector-base bias of 1 V, an intrinsic base sheet resistance (R_bi) of 17 kΩ/□, and an emitter width of 0.9 μm is discussed. This performance level, which represents an increase by almost a factor of 2 in the speed of a Si bipolar transistor, was achieved in a poly-emitter bipolar process by using SiGe for the base material. The germanium was graded in the 45-nm base to create a drift field of approximately 20 kV/cm, resulting in an intrinsic transit time of only 1.9 ps     

Very-high-speed silicon bipolar transistors with in-situ dopedpolysilicon emitter and rapid vapor-phase doping base

We present a detailed study of the performance of very-high-speed silicon bipolar transistors with ultra-shallow junctions formed by thermal diffusion. Devices are fabricated with double-polysilicon self-aligned bipolar technology with U-groove isolation on directly bonded SOI wafers to reduce the parasitic capacitances. Very thin and low resistivity bases are obtained by rapid vapor-phase doping (RVD), which is a vapor diffusion technique using a source gas of B₂H₆. Very shallow emitters are formed by in-situ phosphorus doped polysilicon (IDP) emitter technology with rapid thermal annealing (RTA). In IDP emitter technology, the emitters are formed by diffusion from the in-situ phosphorus doped amorphous silicon layer. Fabricated transistors are found to have ideal I-V characteristics, large current gain and low emitter resistance for a small emitter. Furthermore, a minimum ECL gate delay time of 15 ps is achieved using these key techniques. Analyses of the high performance using circuit and device simulations indicate that the most effective delay components of an ECL gate are cut-off frequency and base resistance. A high cut-off frequency is achieved by reducing the base width and active collector region. In this study, RVD is used to achieve both high cut-off frequency and low base resistance at the same time     

High frequency Pnp AlGaAs/InGaAs heterojunction bipolar transistor with an ultrathin strained base

High performance Pnp AlGaAs/InGaAs heterojunction bipolar transistors (HBTs) have been fabricated. The transistors have a 300 AA strained InGaAs base, with indium composition linearly graded from 0 to 15%. The cutoff frequency, and maximum oscillation frequency for a transistor with emitter area of 2*8 mu m/sup 2/ are measured to be 23.3 GHz and 40 GHz, respectively, at a collector current of -10 mA.<>     

截止频率为238GHz的亚微米InGaAs/InP异质结双极晶体管

研制成功了一种无微空气桥的亚微米InP基异质结双极晶体管(HBT).发展了小于100nm的发射极侧向腐蚀工艺,实现了亚微米的InP基HBT.发射极宽度的减小有效提高了频率特性,发射极面积为0.8μm×15μm的HBT的电流增益截止频率达到了238GHz.发展了基极-集电极的侧向过腐蚀工艺,有效减小了结面积,提高了最大振荡频率.Kirk电流密度达到了3.1mA/μm2.据我们所知,电流增益截止频率是目前国内三端器件中最高的,Kirk电流密度是国内报道的HBT中最高的.这对于HBT器件在超高速电路中的应用具有十分重要的意义.     

High-speed polysilicon emitter—base bipolar transistor

High-speed polysilicon emitter and base electrode Si n-p-n bipolar devices were fabricated showing performances of 55-ps ECL gate delay (FI = FO = 1) and cutoff frequency of 15.6 GHz (at VCE= 3 V, LVCEO= 6.8 V). These devices were built on an oxide-isolated substrate produced by planarizing oxide which is deposited after device Si island etching. The final emitter width is 0.5 µm, and a 1.3-µm-thick arsenic-doped LPCVD epitaxial layer of 0.25 Ω.cm is utilized. Emitter-base (E-B) junctions formed by direct implantations of arsenic and boron ions into a substrate were compared with junctions induced by diffusing dopants from implanted polysilicon. In the case of diffused junctions, an emitter junction depth of less than 500 Å along with a 1000-Å base width can be obtained.     

基极微空气桥和发射极空气桥的InP/InGaAs HBT

报道了具有基极微空气桥和发射极空气桥结构的InP单异质结双极型晶体管(SHBT).由于基极微空气桥和发射极空气桥结构有效地减小了寄生,发射极尺寸为2 μm×12.5 μm的InP HBT的截止频率达到了178GHz.这种器件对高速低功耗的应用非常关键,例如OEIC接收机以及模拟、数字转换器.