High performance ion-implanted low noise GaAs MESFET's

Low noise GaAs MESFET's fabricated by ion-implanting into AsCl3VPE buffer layers have demonstrated not only excellent dc and RF performance, but also a highly reproducible process. The average noise figure and associated gain of four device lots at 12 GHz are 1.6 dB and 10.0 dB, respectively. The standard deviation of noise figure and associated gain from device lot to lot are 0.03 dB and 0.19 dB, respectively. And the standard deviation of noise figure and associated gain from device to device for 35 devices over four lots are 0.13 dB and 0.47dB, respectively. The best device performance includes a 1.25 dB noise figure with 10.46 dB associated gain at 12 GHz for a 0.5 µm × 300 µm FET structure. These results demonstrate the excellent performance and process consistency of ion implanted MESFET's.     

Comment on “On the speed and noise performance of direction-implanted GaAs MESFET's”

Moll comments on the original paper (see ibid., vol.40, pp. 9-17, 1993), stating that the large values of ν_Feng are an artifact of an incorrect analysis and do not represent any physical velocity in the transistor. Most probably, a careful analysis of data for their typical transistors would lead to the notion that the electron velocity is on the order of 1.6 10⁷ cm/s at the drain end of the gated channel. In reply, Feng and Laskar probe the current issues regarding these equations and seek to clarify and validate the equations with 1) The question of velocity overshoot or enhancement in the GaAs channel of HEMT's and MESFET's and its impact upon high speed operation and 2) The delay time analysis technique applied to average velocity extraction     

Thermal noise in ion-implanted MOSFETs

Measurements are reported on high-frequency noise in ion-implanted MOSFETs. The results are interpreted in terms of the thermal noise of the conducting channel.     

Popcorn noise and generation-recombination noise observed in ion-implanted silicon resistors

Experimental results show that, for low currents, the generation-recombination noise component increases with current, and, at higher currents, it decreases inversely with current. For currents greater than a certain value, a generation-recombination noise component is scarcely observed.     

60-GHz noise performance of ion-implanted InxGa1-xAs MESFET's

The authors report the 60-GHz noise performance of low-noise ion-implanted In_xGa_1-xAs MESFETs with 0.25 μm T-shaped gates and amplifiers using these devices. The device noise figure was 2.8 dB with an associated gain of 5.6 dB at 60 GHz. A hybrid two-state amplifier using these ion-implanted In_xGa_1-x As MESFETs achieved a noise figure of 4.6 dB with an associated gain of 10.1 dB at 60 GHz. When this amplifier was biased at 100% I _dss, it achieved 11.5-dB gain at 60 GHz. These results, achieved using low-cost ion-implantation techniques, are the best reported noise figures for ion-implanted MESFETs     

Low-frequency noise of ion-implanted double-drift IMPATT diodes

The low-frequency open circuit noise spectral density S(f) of an ion-implanted 60-GHz double-drift-region IMPATT diode was measured as a function of the dc avalanche current I0. Over an intermediate current range the noise follows an S(f)=a²VB0²/I0relationship where VB0is the reverse breakdown voltage and a²≃4.5 × 10^-20A/Hz.     

Excess noise measurements in ion-implanted silicon resistors

The low-frequency noise spectra of partially annealed boron-implanted silicon resistors with various geometries are measured. The implantation energies are 50, 80 and 110 keV and the doses are 2·5 × 10¹² cm^?2, 1·0 × 10¹³ cm^?2 and 1·0 × 10¹⁴ cm^?2. The spectra exhibit thermal noise and $\text{?}{}^{\mathrm{?n}}$ (excess) noise exclusively. Investigations indicate that the contracts from the implanted layer to the electrode generally contribute small amounts to the total excess noise observed. The excess noise exhibits a strong dependence on the sheet resistance of the layers, while the dependence on substrate bias, implantation energy, and on temperature is relatively weak. A discussion of the results is given in terms of a volume effect. Noise measurements on implanted layers, produced under carefully controlled conditions, show promise as a tool to investigate excess noise.     

Improved noise performance of GaAs MESFET's with selectively ion-implanted n+source regions

Superior microwave performance of 0.5-µm-gate GaAs MESFET's has been attained by a structure with selectively ion-implanted n⁺source regions. The source series resistance is reduced and the noise figure of 2.1 dB is observed at 12 GHz.     

Comparison of noise parameters of diffused and ion-implanted microwave transistors

Two types of implanted microwave transistor structures are outlined, and their behaviour is compared with a totally diffused device. Minimum noise figures for the implanted transistors have been obtained in the range 3.6?4.5 dB at a frequency of 4 GHz.     

Microwave performance of ion-implanted InP JFETs

These devices have a planar structure with the channel and gate regions formed by the selective implantation of silicon and beryllium into an Fe-doped semi-insulating InP substrate. The nominal gate length is 2 μm with a channel doping of 10¹⁷ cm^-3 and thickness of 0.2 μm. The measured values of f_T and f_max are 10 and 23 GHz, respectively. Examination of the equivalent circuit parameters and their variation with bias led to the following conclusions: (a) a relatively gradual channel profile results in lower than desired transconductance, but also lower gate-to-channel capacitance; (b) although for the present devices, the gate length and transconductance are the primary performance-limiting parameters, the gate contact resistance also reduces the power gain significantly; (c) the output resistance appears lower than that of an equivalent GaAs MESFET, and requires a larger V_DS to reach its maximum value; and (d) a dipole layer forms and decouples the gate from the drain with a strength that falls between that of previously reported GaAs MESFETs and InP MESFETs     

Alternate explanation of 1f noise in ion-implanted MOSFETs

$\text{1}\text{f}$ noise in ion-implanted MOSFETs is not explained in terms of mobility fluctuation noise but as number fluctuation noise governed by a transition from surface channel flow at low drain bias to buried channel flow near the drain at elevated drain bias.     

Magnetotransconductance profiling of mobility and doping in GaAsMESFETs

Electron mobility profiles of GaAs MESFETs have been measured using the magnetotransconductance technique and corrected using in situ measurements of parasitic resistances. It is shown that with this technique both mobility and carrier density profiles versus depth can be calculated without C-V data. This enables complete mobility and carrier density profiles to be obtained on short-gate-length packaged devices without the inherent difficulties of the C-V method and its attendant inaccuracies near the active layer-substrate interface. The results for two commercial packaged devices at room temperature, which indicate mobilities of 3500 to 4500 cm²/V/s and peak carrier concentrations of 1.2 to 2.0×10¹⁷ cm^-3, are given     

On the noise performance of bipolar transistors in untuned amplifiers

From a generalized approach this paper reexamines the noise performance of bipolar transistors in untuned amplifiers. New results are obtained for the upper corner frequency which fully characterize the frequency dependent noise figure curves under conditions of arbitrary and optimum source conductance termination. The effects of the collector bias current on the minimum noise figure, the optimum source conductance and the upper noise corner frequency are presented both analytically and graphically. The results also include the effects of source capacitance on noise figures. A systematic design of low-noise untuned low-pass amplifiers with desired gain-bandwidth performance can be readily achieved with the help of the results presented.     

Measurements of residual defects and 1/f noise in ion-implanted p-channel MOSFET's

This paper describes the measurements of excess noise and residual defects of extremely low concentrations (<1 × 10⁹cm^-2) in ion-implanted p-channel MOSFET's. The activation energy and the density of the residual defects after high-temperature annealing were measured using a transient capacitance technique. The test FET's were ion-implanted with fluences of 5 × 10¹¹to 4 × 10¹²using³¹p⁺,¹¹B⁺, or²⁸Si⁺species. A post-implant anneal was carried out in an N2or an Ar ambient for 20 min at various temperatures. For¹¹B⁺-implanted MOSFET's after annealing above 1000°C, a high residual defect concentration was observed near the conduction band edge; whereas after annealing the defect density as a result of²⁸Si⁺or³¹p⁺implantation was equal to that of control MOSFET's. The density-of-state data agree with the equilibrium measurements of excess (1/f) noise power. The excess noise was measured as a function of the drain current. The distribution of1/fnoise power versus potential minimum of holes in the equilibrium condition is similar to that of interface state density. In nonequilibrium operation, a reduction of excess noise was achieved owing to the presence of buried channel created by ion implant.     

On the performance of ultra-wide-band signals in Gaussian noise anddense multipath

An ultra-wide-band (UWB) signal is characterized by a radiated spectrum with a very wide bandwidth around a relatively low center frequency. In this paper, we study the reduced fading margin property of UWB signals. To evaluate the fading margin, we compare the performance of UWB signals in an environment with only additive white Gaussian noise (AWGN) versus the performance of UWB signals in a dense multipath environment with AWGN. The assumption here is that the presence of multipath causes a small increase in the signal-to-noise ratio required to achieve reasonable levels of bit error rate. A numerical example confirms this assumption, more specifically, the example shows that to achieve a bit error rate equal to 10^-5, we require about 13.5 dB in the AWGN case and about 15 dB in the multipath case, resulting in a fading margin of just 1.5 dB. This small fading margin can be understood by the ability of the UWB signal to resolve the dense multipath     

The influence of ion-implanted profiles on the performance of GaAsMESFET's and MMIC amplifiers

The RF small-signal performance of GaAs MESFETs and MMIC amplifiers as a function of various ion-implanted profiles is theoretically and experimentally investigated. Implantation energy, dose, and recess-depth influence are theoretically analyzed with the help of a novel device simulator. The performance of MMIC amplifiers processed with various energies, doses, recess depths, and bias conditions is discussed and compared to experimental characteristics. Some criteria are proposed for the choice of implantation conditions and process in order to optimize the characteristics of ion-implanted FETs and to realize process-tolerant MMIC amplifiers     

On the frequency dependent drain conductance of ion-implanted GaAs MESFETs

The effect of MESFET structure on the frequency dispersion of drain conductance (g/sub d/) was examined, It was found that a shorter gate length, lower buried p-layer concentration, lower sheet resistance of n/sup +/ layer, and thinner active layer thickness are effective in suppressing the frequency dependent g/sub d/. These phenomena are explained by the presence of deep traps in the depletion layer between the semi-insulating substate and active layer. We also show that the cross-point change of eye-pattern for density of input signal in logic ICs is due to frequency dependent g/sub d/ The cross-point change between mark ratio of 1/8 and 7/8 shows a linear relationship with gd/sub RF//gd/sub dc/ (the ratio of the drain conductance at RF and dc input), These results indicate that an optimized device structure with g/sub d/ small frequency dispersion can be used to realize high-speed and high quality logic ICs.     

Low RF noise and power loss for ion-implanted Si having an improved implantation process

Very-low-transmission line noise of <0.25 dB at 18 GHz and low power loss /spl les/0.6 dB at 110 GHz have been measured on transmission lines fabricated on proton-implanted Si. In contrast, a standard Si substrate gave much higher noise of 2.5 dB and worse power loss of 5 dB. The good RF integrity of proton-implanted Si results from the high isolation impedance to ground, as analyzed by an equivalent circuit model. The proton implantation is also done after forming the transmission lines at a reduced implantation energy of /spl sim/4 MeV. This enables easier process integration into current VLSI technology.     

Calculations of high-speed performance for submicrometer ion-implanted GaAs MESFET devices

Interest in high-speed logic devices has motivated a study of various device geometries in order to potentially improve the cutoff frequency of GaAs MESFET devices. In this paper, a two-dimensional model is used as a tool to investigate the effect of modifications of device dimensions on device performance. Modifying the device geometries by reducing the spacing between the gate and the contacts was found to improve the cutoff frequency slightly. Calculations are also presented for a device scaled to a channel length of 0.2 µm, where an fTof about 60 GHz is predicted.