High performance GaAs JFET with shallow implanted Cd-gate

Shallow p⁺-regions in GaAs, formed by Cd ion implantation, have been used as the gate region for GaAs JFETs. 0.7 μm gate length JFETs demonstrated a transconductance of 165 mS/mm a saturation current of 130 mA/mm, an f_t of 26 GHz, and an f _max of 42 GHz. These frequency metrics are superior to previous Zn-gate JFETs of similar dimensions     

Comparison of Mg and Zn gate implants for GaAs n-channel junction field effect transistors

Zinc and magnesium implants into GaAs were profiled with secondary ion mass spectroscopy and etching capacitance-voltage to measure the as-implanted and annealed profiles for the eventual formation of shallow p⁺/n junction gates for junction field effect transistors (JFETs). The larger mass of the zinc ions results in shorter projected range with significantly less tailing than magnesium implants. High dose, shallow zinc implants annealed under tungsten gate metal showed good activation with negligible diffusion. The improved profile of the zinc implant, as compared to a similar magnesium implant, allowed a tighter JFET design with increased performance. Zn gated n-channel enhancement mode GaAs JFETs with 0.9 μm gate lengths showed transconductances up to 200 mS/ mm with a f_t of 18 GHZ and a f_max of 37 GHz. The performance of these self-aligned fully implanted JFETs compare favorably with comparably sized implanted MESFETs.     

Noise performance of low power 0.25 micron gate ion implantedD-mode GaAs MESFET for wireless applications

We report on the noise performance of low power 0.25 μm gate ion implanted D-mode GaAs MESFETs suitable for wireless personal communication applications. The 0.25 μm×200 μm D-mode MESFET has a f_t of 18 GHz and f_max of 33 GHz at a power level of 1 mW (power density of 5 mW/mm). The noise characteristics at 4 GHz for the D-mode MESFET are F_min=0.65 dB and G_assoc =13 dB at 1 mW. These results demonstrate that the GaAs D-mode MESFET is also an excellent choice for low power personal communication applications     

Charge control, DC, and RF performance of a 0.35-μmpseudomorphic AlGaAs/InGaAs modulation-doped field-effecttransistor

The authors describe a study of charge control in conjunction with DC and RF performance of 0.35-μm-gate-length pseudomorphic AlGaAs/InGaAs MODFETs. Using C-V measurements, they estimate that a two-dimensional electron gas (2DEG) with density as high as 1.0×10¹² cm^-2 can be accumulated in the InGaAs channel at 77 K before the gate begins to modulate parasitic charges in the AlGaAs. This improvement in charge control of about 10-30% over a typical AlGaAs/GaAs MODFET may partially be responsible for the superior DC and RF performance of the AlGaAs/InGaAs MODFET. At room temperature, the devices give a maximum DC voltage gain g _m/g_d of 32 and a current gain cutoff frequency f_T of 46 GHz. These results are state of the art for MODFETs of similar gate length     

Fabrication and characteristics of a GaInP/GaAs heterojunctionbipolar transistor using a selective buried sub-collector

A C-doped GaInP/GaAs heterojunction bipolar transistor (HBT) with a selective buried sub-collector has been fabricated by two growth steps. The active HBT region was made on the selective buried sub-collector layer with minimum overlap of the extrinsic base and the sub-collector region resulting in substantial reduction of the base-collector capacitance. The experiment shows that the base-collector capacitance is reduced to about half of that of a conventional HBT while the base resistance remains unchanged resulting in a 40-50% increase in the maximum oscillation frequency. Both DC and RF characteristics are investigated and compared with a conventional HBT. A current gain of 40, cutoff frequency of 50 GHz and maximum oscillation frequency of 140 GHz were obtained for the GaInP/GaAs HBT. It is demonstrated that the selective buried sub-collector provides an effective means for enhancing RF performance of an HBT     

High-speed small-scale InGaP/GaAs HBT technology and itsapplication to integrated circuits

We have developed the advanced performance, small-scale InGaP/GaAs heterojunction bipolar transistors (HBTs) by using WSi/Ti base electrode and buried SiO₂ in the extrinsic collector. The base-collector capacitance C_BC was further reduced to improve high-frequency performance. Improving the uniformity of the buried SiO ₂, reducing the area of the base electrode, and optimizing the width of the base-contact enabled us to reduce the parasitic capacitance in the buried SiO₂ region by 50% compared to our previous devices. The cutoff frequency f_T of 156 GHz and the maximum oscillation frequency f_max of 255 GHz were obtained at a collector current I_C of 3.5 mA for the HBT with an emitter size S_E of 0.5×4.5 μm², and f_T of 114 GHz and f_max of 230 GHz were obtained at I_C of 0.9 mA for the HBT with S_E of 0.25×1.5 μm². We have also fabricated digital and analog circuits using these HBTs. A 1/8 static frequency divider operated at a maximum toggle frequency of 39.5 GHz with a power consumption per flip-flop of 190 mW. A transimpedance amplifier provides a gain of 46.5 dB·Ω with a bandwidth of 41.6 GHz at a power consumption of 150 mW. These results indicate the great potential of our HBTs for high-speed, low-power circuit applications     

10GHz GaAs JFET dual-modulus prescalar IC

A divide-by-256/258 dual-modulus prescalar IC has been successfully fabricated using enhancement-mode GaAs JFETs. The maximum operation frequency of 10.4 GHz is obtained by a 0.5 mu m gate length and buried p-layer JFET technology. The prescalar IC has sufficient operational margin to make it compatible with Si bipolar ECL circuits over a wide frequency range.<>     

High-speed InGaP/GaAs heterojunction bipolar transistors withburied SiO2 using WSi as the base electrode

High-speed InGaP/GaAs heterojunction bipolar transistors (HBT's) with a small emitter area are described. WSi is used as the base electrode to fabricate HBT's with a narrow base contact width and a buried SiO₂ structure. An HBT with an emitter area of 0.8×5 μm exhibited an f_T of 105 GHz and an f_max of 120 GHz. These high values are obtained due to the reduction of C_BC by using buried SiO₂ with a narrow base contact width, indicating the great potential of GaAs HBT's for high-speed and low-power circuit applications     

An all-implanted, self-aligned, GaAs JFET with a nonalloyedW/p+-GaAs ohmic gate contact

We describe a self-aligned, refractory metal gate contact, enhancement mode, GaAs junction field effect transistor (JFET) where all impurity doping was done by ion implantation. Processing conditions are presented for realizing a high gate turn-on voltage (~1.0 V at 1 mA/mm of gate current) relative to GaAs MESFET's. The high gate turn-on voltage is the result of optimizing the p⁺-gate implant and anneal to achieve a nonalloyed ohmic contact between the implanted p⁺-GaAs and the sputter deposited tungsten gate contact. Initial nominally 1.0 μm×50 μm n-JFET's have a transconductance of 85 mS/mm and f_t of 11.4 GHz     

High-speed InGaP/GaAs HBTs with a strained InxGa1-xAs base

A self-aligned InGaP/GaAs heterojunction bipolar transistor with a compositionally graded In_xGa_1-xAs base has been demonstrated with f_T=83 GHz and f_max=197 GHz. To our knowledge, these results are the highest reported for both parameters in InGaP/GaAs HBT's. The graded base, which improves electron transport through the base, results in a DC current gain and a cutoff frequency which are 100% and 20% higher, respectively, than that achieved by an identical device with a nongraded base. The high f_max results from a heavily doped base, self-aligned base contacts, and a self-aligned collector etch. These results demonstrate the applicability of InGaP/GaAs HBT's in high-speed microwave applications     

Super-low-noise performance of direct-ion-implanted 0.25-μm-gateGaAs MESFET's

The authors report on advanced ion implantation GaAs MESFET technology using a 0.25-μm `T' gate for super-low-noise microwave and millimeter-wave IC applications. The 0.25×200-μm-gate GaAs MESFETs achieved 0.56-dB noise figure with 13.1-dB associated gain at 50% I_DSS and 0.6 dB noise figure with 16.5-dB associated gain at 100% I_DSS at a measured frequency of 10 GHz. The measured noise figure is comparable to the best noise performance of AlGaAs/GaAs HEMTs and AlGaAs/InGaAs/GaAs pseudomorphic HEMTs     

Direct ion-implanted 0.12 μm GaAs MESFET with ft of121 GHz and fmax of 160 GHz

An 0.12 μm gate length direct ion-implanted GaAs MESFET exhibiting excellent DC and microwave characteristics has been developed. By using a shallow implant schedule to form a highly-doped channel and an AsH₃ overpressure annealing system to optimize the shallow dopant profile, the GaAs MESFET performance was further improved. Peak transconductance of 500 mS/mm was obtained at I_ds =380 mA/mm. A noise figure of 0.9 dB with associated gain of 8.9 dB were achieved at 18 GHz. The current gain cutoff frequency f_max of 160 GHz indicates the suitability of this 0.12 μm T-gate device for millimeter-wave IC applications     

Metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with a novelcomposite channels design

We report on fabrication and performance of novel 0.13 μm T-gate metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with composite InGaAs channels, combining the superior transport properties of In_0.52Ga_0.48As with low-impact ionization in the In_0.32Ga_0.68As subchannel. These devices exhibit excellent DC characteristics, high drain currents of 750 mA/mm, extrinsic transconductances of 600 mS/mm, combined with still very low output conductance values of 20 mS/mm, and high channel and gate breakdown voltages. The use of a composite InGaAs channels leads to excellent cut-off frequencies: f_max of 350 GHz and an f_T 160 GHz at V_DS=1.5 V. These are the best microwave frequency results ever reported for any FET on GaAs substrate     

High-Frequency Si-MOSFET's

Silicon (Si-) MOSFET's with 0.8-mu m channel, made by conventional technology and optimized for microwave applications, have noise figures of 3.7 dB at 4 GHz and maximum frequencies of oscillation of 10 to 12 GHz. The noise and radio-frequency (RF) small signal performance are only slightly affected by double ion implantation of the channel region, used to shift the threshold voltage from - 2 V to +0.2 V. Excess noise is generated in the implanted MOSFET's for lower V/sub DS/ values than in unimplanted ones. The variation of the noise parameters with drain current is lower in implanted devices. The RF equivalent circuit analysis indicates negligible parasitic lead resistances, but high feedback capacitance. A comparison with GaAs MESFET's of the buried channel type showed the Si-MOSFET's to have lower third-order harmonic distortion when driven by a 1-GHz signal source.     

Heavily carbon-doped InGaP/GaAs HBT's with buried polycrystallineGaAs under the base electrode

This paper describes a new approach to fabricating InGaP/GaAs heterojunction bipolar transistors (HBT's) with a high cutoff frequency (f_T), high maximum oscillation frequency (f_max), and low external collector capacitance (C_bc). To attain a high f_T and f_max, a heavy carbon-doping (1.3×10²⁰ cm^-3) technique was used with a thin (30-nm-thick) GaAs base layer, while for low C_bc, low-temperature gas-source molecular-beam epitaxial growth on SiO₂ -patterned substrates was used to bury high-resistance polycrystalline GaAs under the base electrode. An f_T of 120 GHz and an f_max of 230 GHz were achieved for three parallel 0.7×8.5 μm HBT's with an undoped-collector structure, and an f _T of 170 GHz and an f_max of 160 GHz were obtained for a single 0.9×10 μm HBT with a ballistic-collection-transistor structure. Compared to HBT's without buried poly-GaAs, the maximum stable gain was improved by 1.2 dB in the 0.7×8.5 μm HBT and by 2.3 dB in the 0.9×10 μm HBT due to the reduction in C_bc. These results show the high potential of the proposed HBT's for high-speed digital and broadband-amplifier applications     

Ultrahigh-frequency performance of submicrometer-gate ion-implantedGaAs MESFETs

A study of the high-frequency performance of short-gate ion-implanted GaAs MESFETs with gate lengths of 0.3 and 0.5 μm is discussed. Excellent DC and microwave performance have been achieved with an emphasis on the reduction of effective gate length during device fabrication. From f_t of 83 and 48 GHz for 0.3-0.5-μm gate devices, respectively, an electron velocity of 1.5×10⁷ cm/s is estimated. An f_t of 240 GHz is also projected for a 0.1-μm-gate GaAs MESFET. These experimental results are believed to be comparable to those of the best HEMTs (high-electron-mobility transistors) reported and higher than those generally accepted for MESFETs     

A high-frequency GaInP/GaAs heterojunction bipolar transistor withreduced base-collector capacitance using a selective buriedsub-collector

A C-doped GaInP/GaAs HBT using a selective buried sub-collector has been fabricated by two growth steps. The device was fabricated with minimum overlap of the extrinsic base and the sub-collector region to reduce base-collector capacitance. The experiment shows that the base collector capacitance is reduced to about half of that of an HBT without selective buried sub-collector while the base resistance remains unchanged. A current gain of 35, f_T of 50 GHz and f_max of 140 GHz are obtained with this technology     

A new approach to fabrication of GaAs JFETs

A new approach to JFETs is preparing gallium assenide junction field-effect transistor (JFET) presented in this paper, applying Be ion implantation for the first time along with a method of flat and homogeneous ohmic metallization. Several characteristics of FET I–V curve are also discussed.It is revealed that Be ion implantation is sufficiently feasible to obtain a buried p-type gate for the GaAs JFET. Ohmic metallization to GaAs is improved in flatness and homogeneity by simultaneous heating of substrates with Au/Ge deposition. An ion milling process for fine patterning associated with the improved metallization, proves to be useful for device micro-technology. Finally, d.c. characteristics comparable to those of the MESFET are demonstrated by the fabricated JFET, with marked advantages in the process.     

3-mm double-heterojunction microwave power HEMT fabricated byselective RIE

Current-voltage and initial RF measurements are presented on a double-heterojunction HEMT (high-electron-mobility transistor) structure designed for power MMIC applications. The device structure is grown by molecular-beam epitaxy and uses a spatially variant superlattice to improve the performance of the inverted AlGaAs/GaAs interface. Gate recessing is achieved using a hybrid wet-chemical selective dry etching process. For selective dry etching, reactive ion etching with a >600:1 selectivity for GaAs over AlGaAs is used to control the recess depth. The room temperature DC characteristics for a 3-mm power FET (0.7- μm gate) display an I_dss of 370 mA/mm, a peak transconductance of 180 mS/mm, and a maximum gate-to-drain breakdown of 22 V. Large-signal microwave measurements at 5.5 GHz yielded a saturated output power of 1.3 W (31.2 dBm), 8.3-dB large-signal gain, and a peak power-added efficiency of 55%     

High-speed, low-noise InGaP/GaAs heterojunction bipolar transistors

We have demonstrated self-aligned InGaP/GaAs heterojunction bipolar transistors (HBT's) with excellent dc, microwave, and noise performance. A 3×10 μm² emitter finger device achieved a cutoff frequency of f_T=66 GHz and a maximum frequency of oscillation of f_max=109 GHz. A minimum noise figure of 1.12 dB and an associated gain of 11 dB were measured at 4 GHz. These results are the highest combined f_T+f_max and the lowest noise figure reported for an InGaP/GaAs HBT and are attributed to material quality and the use of self-aligned base contacts. These data clearly demonstrate the viability of InGaP/GaAs HBT's for high-speed, low-noise circuit applications