0.33-μm gate-length millimeter-wave InP-channel HEMTs with highf1 and fmax

The fabrication of 0.33-μm gate-length AlInAs/InP high electron mobility transistors (HEMTs) is reported. These InP-channel devices have f_t values as high as 76 GHz, f_max values of 146 GHz, and maximum stable gains of 16.8, 14, and 12 dB at 10, 18, and 30 GHz, respectively. The extrinsic DC transconductances are as high as 610 mS/mm; with drain-source breakdown voltages exceeding 10 V. The effective electron velocity in the InP channel is estimated to be at least 1.8×10⁷ cm/s, while the f_tL_g product is 29 GHz-μm. These results are comparable to the best reported results for similar InGaAs-channel devices     

Si/a-Si:H heterojunction microwave bipolar transistors with cut-offfrequencies ft above 5 GHz

The fabrication of a silicon heterojunction microwave bipolar transistor with an n⁺ a-Si:H emitter is discussed, and experimental results are given. The device provides a base sheet resistance of 2 kΩ/□ a base width 0.1 μm, a maximum current gain of 21 (V_CE=6 V, I_c=15 mA), and an emitter Gummel number G _E of about 1.4×10¹⁴ Scm^-4. From the measured S parameters, a cutoff frequency f_t of 5.5 GHz and maximum oscillating frequency f_max of 7.5 GHz at V_CE=10 V, I_c=10 mA are obtained     

High/fmax collector-up AlGaAs/GaAsheterojunction bipolar transistors with a heavily carbon-doped basefabricated using oxygen-ion implantation

AlGaAs/GaAs collector-up heterojunction bipolar transistors (HBTs) with a heavily carbon-doped base layer were fabricated using oxygen-ion implantation and zinc diffusion. The high resistivity of the oxygen-ion-implanted AlGaAs layer in the external emitter region effectively suppressed electron injection from the emitter, allowing collector current densities to reach values above 10⁵ A/cm ². For a transistor with a 2-μm×10-μm collector, f_T was 70 GHz and f_max was as high as 128 GHz. It was demonstrated by on-wafer measurements that the first power performance of collector-up HBTs resulted in a maximum power-added efficiency of as high as 63.4% at 3 GHz     

Hot-electron InGaAs/InP heterostructure bipolar transistors withfT of 110 GHz

A hot-electron InGaAs/InP heterostructure bipolar transistor (HBT) is discussed. A unity-current-gain cutoff frequency of 110 GHz and a maximum frequency of oscillation of 58 GHz are realized in transistors with 3.2×3.2-μm² emitter size. Nonequilibrium electron transport, with an average electron velocity approaching 4×10⁷ cm/s through the thin (650 Å) heavily doped (p=5×10¹⁹ cm^-3) InGaAs base and 3000-Å-wide collector space-charge region, results in a transit delay of 0.5 ps corresponding to an intrinsic cutoff frequency of 318 GHz     

Quarter-micrometer gate ion-implanted GaAs MESFET's with an f1 of 126 GHz

The fabrication and characterization of a 0.25-μm-gate, ion-implanted GaAs MESFET with a maximum current-gain cutoff frequency f_t of 126 GHz is reported. Extrapolation of current gains from bias-dependent S-parameters at 70-100% of I _dss yields f₁'s of 108-126 GHz. It is projected that an f₁ of 320 GHz is achievable with 0.1-μm-gate GaAs MESFETs. This demonstration of f₁'s over 100 GHz with practical 0.25-μm gate length substantially advances the high-frequency operation limits of short-gate GaAs MESFETs     

Bulk and surface 1/f noise

The 1/f noise of an n-type silicon MOSFET has been studied under conditions ranging from accumulation to depletion at 300 K. The experimental results are interpreted in terms of a bulk phenomenon and are characterized by Hooge's empirical 1/f noise parameter α with values between 10^-7 and 10^-5. The α value for surface conduction at strong accumulation can be at least one order of magnitude larger than the value for bulk conduction     

Process integration and device performance of a submicrometerBiCMOS with 16-GHz ft double poly-bipolar devices

Submicrometer-channel CMOS devices have been integrated with self-aligned double-polysilicon bipolar devices showing a cutoff frequency of 16 GHz. n-p-n bipolar transistors and p-channel MOSFETs were built in an n-type epitaxial layer on an n⁺ buried layer, and n-channel MOSFETs were built in a p-well on a p⁺ buried layer. Deep trenches with depths of 4 μm and widths of 1 μm isolated the n-p-n bipolar transistors and the n- and p-channel MOSFETs from each other. CMOS, BiCMOS, and bipolar ECL circuits were characterized and compared with each other in terms of circuit speed as a function of loading capacitance, power dissipation, and power supply voltage. The BiCMOS circuit showed a significant speed degradation and became slower than the CMOS circuit when the power supply voltage was reduced below 3.3 V. The bipolar ECL circuit maintained the highest speed, with a propagation delay time of 65 ps for C_L=0 pF and 300 ps for C_L=1.0 pF with a power dissipation of 8 mW per gate. The circuit speed improvements in the CMOS circuits as the effective channel lengths of the MOS devices were scaled from 0.8 to 0.4 μm were maintained at almost the same ratio     

89-GHz fT room-temperature silicon MOSFETs

The authors report the implementation of deep-submicrometer Si MOSFETs that at room temperature have a unity-current-gain cutoff frequency (f_T) of 89 GHz, for a drain-to-source bias of 1.5 V, a gate-to-source bias of 1 V, a gate oxide thickness of 40 Å, and a channel length of 0.15 μm. The fabrication procedure is mostly conventional, except for the e-beam defined gates. The speed performance is achieved through an intrinsic transit time of only 1.8 ps across the active device region     

0.2-μm gate-length atomic-planar doped pseudomorphic Al0.3Ga0.7As/In0.25Ga0.75As MODFETswith fT over 120 GHz

The authors report the DC and RF performance of nominally 0.2-μm-gate length atomic-planar doped pseudomorphic Al_0.3Ga_0.7As/In_0.25Ga_0.75As modulation-doped field-effect transistors (MODFETs) with f_T over 120 GHz. The devices exhibit a maximum two-dimensional electron gas (2 DEG) sheet density of 2.4×10¹² cm^-2, peak transconductance g _m of 530-570 mS/mm. maximum current density of 500-550 mA/mm, and peak current-gain cutoff frequency f_T of 110-122 GHz. These results are claimed to be among the best ever reported for pseudomorphic AlGaAs/InGaAs MODFETs and are attributed to the high 2 DEG sheet density, rather than an enhanced saturation velocity, in the In_0.25Ga_0.75As channel     

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     

1/f noise in GaAs filaments

A typical 1/f noise is excited in GaAs filament with the Hooge noise parameter of about α_H=2×10^-3 . The noise level increases in proportion to the square of the terminal voltage, and decreases approximately in inverse proportion to the total number of carriers within the device. A transition from the typical 1/f noise characteristics to the diffusion noise characteristics of MESFETs was observed when the electric field was increased above 1 kV/cm. The noise parameters were also investigated as a function of the device width between 2 and 200 μm. Deep levels within the n-GaAs active layer and the high electric field are the main factors of the nonideal 1/f characteristics     

1/f noise in MODFETs at low drain bias

The 1/f noise in normally-on MODFETs biased at low drain voltages is investigated. The experimentally observed relative noise in the drain current S_I/I² versus the effective gate voltage V_G=V_GS-V_off shows three regions which are explained. The observed dependencies are S_I/I²∝V_G ^m with the exponents m=-1, -3, 0 with increasing values of V_G. The model explains m =-1 as the region where the resistance and the 1/f noise stem from the 2-D electron gas under the gate electrode; the region with m=0 at large V_G or V_GS≅0 is due to the dominant contribution of the series resistance. In the region at intermediate V_G , m=-3, the 1/f noise stems from the channel under the gate electrode, and the drain-source resistance is already dominated by the series resistance     

Fabrication of 200-GHz fmax resonant-tunnelingdiodes for integration circuit and microwave applications

Room-temperature current densities of 1.3×10⁵ A/cm² and peak-to-valley ratios of 2.5 have been achieved for resonant tunneling diodes (RTDs) in the GaAs/AlAs material system. The devices were fabricated in a microwave-compatible process using topside contacts and a semi-insulating substrate to allow device integration. Proton implantation creates a nonconducting surface compatible with high-frequency coplanar transmission lines and other passive microwave structures     

Importance of source and drain resistance to the maximum fT of millimeter-wave MODFETs

The usual approximate expression for measured f_T =[g_m/2π (C_gs+C _gd)] is inadequate. At low drain voltages just beyond the knee of the DC I-V curves, where intrinsic f _t is a maximum for millimeter-wave MODFETs, the high values of C_gd and G_ds combine with the high g_m to make terms involving the source and drain resistance significant. It is shown that these resistances can degrade the measured f_T of a 0.30-μm GaAs-AlGaAs MODFET from an intrinsic maximum f_T value of 73 GHz to a measured maximum value of 59 GHz. The correct extraction of maximum f_T is essential for determining electron velocity and optimizing low-noise performance     

Effect of reduced temperature on the fT ofAlGaAs/GaAs heterojunction bipolar transistors

The high-frequency and DC performances of single-heterojunction Al _0.25Ga_0.75As/GaAs heterojunction bipolar transistors (HBTs) have been measured at temperatures between 300 and 110 K. It is found that the maximum unity-current-gain cutoff frequency increases from 26 GHz at 300 K to 34 GHz at 110 K. It is shown that electron diffusion as determined from the majority-carrier mobility does not accurately estimate the base transit time, at least until corrections for degeneracy and minority-carrier mobility enhancement are included. Reasonable agreement is obtained assuming that base transport is limited by the thermal velocity of electrons at reduced temperatures     

A low-noise K-Ka band oscillator AlGaAs/GaAsheterojunction bipolar transistors

The design considerations, fabrication process, and performance of the first K-Ka-band oscillator implemented using a self-aligned AlGaAs/GaAs heterojunction bipolar transistor (HBT) are described. A large-signal time-domain-based design approach has been used which applies a SPICE-F simulator for optimization of the oscillator circuit parameters for maximum output power. The oscillator employs a 2×10-μm² emitter AlGaAs/GaAs HBT that was fabricated using a pattern inversion technology. The HBT has a base current 1/f noise power density lower than 1×10^-20 A²/Hz at 1 kHz and lower than 1×10^-22 A/²/Hz at 100 kHz for a collector current of 1 mA. The oscillator, which is composed of only low-Q microstrip transmission lines, has a phase noise of -80 dBc/Hz at 100 kHz off carrier when operated at 26.6 GHz. These results indicate the applicability of the HBTs to low-phase-noise monolithic oscillators at microwave and millimeter-wave frequencies, where both Si bipolar transistors and GaAs FETs are absent     

Reduction of ft by nonuniform base bandgapnarrowing

Analytical and simulation results are presented to illustrate qualitatively the effect of doping on base transit time. Nonuniform base bandgap narrowing (BGN) in silicon bipolar transistors can give rise to an electric field that is comparable to and against the built-in field. The base transit time τ is subsequently increased, leading to a deterioration of the cutoff frequency f₁. It is shown that the BGN effectively reduces the impurity profile grading factor K and subsequently the transit-time coefficient η. Physically, the minority carriers can be thought of as moving in a new profile characterized by a reduced η but in the absence of BGN. Unlike earlier investigations which also consider effective BGN dopings but ignore the field effects, this treatment includes their impact on the minority-carrier base transit time. For a steep exponential profile with strong BGN, an increase of η by a factor 3.57 at 300 K is calculated. Device simulations predict a smaller f_t reduction factor of 1.5 for more general profiles     

W-band low-noise InAlAs/InGaAs lattice-matched HEMTs

Very low-noise 0.15-μm gate-length W-band In_0.52 Al_0.48As/In_0.53Ga_0.47As/In _0.52Al_0.48As/InP lattice-matched HEMTs are discussed. A maximum extrinsic transconductance of 1300 mS/mm has been measured for the device. At 18 GHz, a noise figure of 0.3 dB with an associated gain of 17.2 dB was measured. The device also exhibited a minimum noise figure of 1.4 dB with 6.6-dB associated gain at 93 GHz. A maximum available gain of 12.6 dB at 95 GHz, corresponding to a maximum frequency of oscillation, f_max, of 405 GHz (-6-dB/octave extrapolation) in the device was measured. These are the best device results yet reported. These results clearly demonstrate the potential of the InP-based HEMTs for low-noise applications, at least up to 100 GHz     

Bias dependence of fT and fmax in anIn0.52Al0.48As/n+-In0.53Ga0.47As MISFET

Detailed microwave characterization of a recently fabricated In _0.52Al_0.48As/n⁺-In_0.53Ga _0.47As MISFET reveals that high values of current-gain cutoff frequency (f_T) and unilateral-gain cutoff frequency (f_max) are obtained for a broad range of gate bias voltage values. A significant peak in f_T and f _max has also been observed at high gate-source bias values. The peak coincides with the onset of electron accumulation at the heterointerface and is attributed to reduced ionized impurity scattering coupled with reduced drain conductance. This result suggests an improved device structure that optimizes operation in the accumulation regime     

Correlation between 1/f noise and hFElong-term instability in silicon bipolar devices

Accelerated life tests with high-temperature storage and electric aging for n⁺-p-n silicon planar transistors were carried out. Current gain h_FE increases monotonously with time during the tests, and the h_FE drift is correlated with initial measured 1/f noise in the transistors, i.e. the drift amount significantly increases with the increase of noise level. The correlation coefficient of relative drift Δh_FE /h_FE and 1/f noise spectral density S_iB(f) is far larger than that of Δ h_FE/h_FE and initial DC parameters of the transistors. A quantitative theory model for the h _FE drift has been developed and explains the h _FE drift behavior in the tests, which suggests that the h _FE drift and 1/f noise can be attributed to the same physical origin, and both are caused by the modulation of the oxide traps near the Si-SiO₂ interface to Si surface recombination. 1/f noise measurement, therefore, may be used as a fast and nondestructive means to predict the long-term instability in bipolar transistors