Low frequency noise in junction field effect transistors

Low frequency noise in four-terminal JFETs has been measured as a function of substrate (second gate) bias with temperature and drain current as additional variables. Sharp peaks of noise have been observed at some values of gate bias. The mechanism of low frequency noise caused by Schockley-Read-Hall (SRH) centres and the significance of charge capture processes in and near the channel are discussed. The experimental results show that most of the excess low frequency noise is caused by SRH centres situated in the transition region between the channel and the fully depleted region of the gate-channel junctions. In JFETs with gate-widths of 1000 μm or less the noise caused by unit electronic charge fluctuations at invidual SRH centres can be readily observed.     

Gate noise in field effect transistors at moderately high frequencies

At higher frequencies the gate noise of a field effect transistor increases rapidly with increasing frequency. This effect is here attributed to the thermal noise of the conducting channel and is caused by the capacitive coupling between the channel and the gate. The noise is represented by gate and drain noise current generators igand id, respectively; an approximation method is developed that allows calculation of ig², id²and ig× idfor moderately high frequencies. The correlation coefficient of igand idis imaginary and amounts to about 0.40j under saturated conditions, ig²can be expressed in terms of the noise resistance Rn, and the gate-source capacitance Cgs.It is shown that the correlation has only a slight influence on the noise figure F and that (Fmin- 1) varies as ωCgsRnover a wide frequency range.     

Thermal noise in high electron mobility transistors

Thermal noise in HEMT devices is evaluated for arbitrary drain voltages including saturation. The results closely resemble those for MOSFETS. The consequences of hot electron effects are indicated, and the effects due to feedback via the series resistance R_s on the source side of the channel are evaluated. For very short channels the noise resistance R_n can be relatively large because the transconductance g_max at saturation is so much smaller than the drain conductance g_d0 at zero drain bias.     

Effects of electron bombardment on the noise in junction gate field effect transistors

The effects of electron bombardment on the various noise sources in n-type channel and p-type channel junction gate field effect transistors (JFET's) have been investigated in detail. It is shown that generation recombination (g-r) noise is the most sensitive noise source to electron bombardment. The noise frequency spectra obtained after each bombardment level are shown to be characterized by two distinct time constants, one due to traps in the gate channel depletion region and the other due to traps in the channel.     

Correlation between low-frequency noise and low-temperature performance of two-dimensional electron gas FET's

We report here on low-frequency (LF) noise of GaAs/ GaAlAs TEGFET's. Present investigations show that this noise is not inherently lower in TEGFET's than in MESFET's. Moreover, the bias and frequency dependence of the noise was found to indicate that traps in GaAlAs have a fundamental influence on LF noise. A close correlation is subsequently observed between the noise level at ambient temperature and the TEGFET static and dynamic performances at low temperature (130 K).     

The noise properties of high electron mobility transistors

A simple analytic model for the HEMT, based on the Pucel theory for MESFET's, is developed which can be used to calculate the noise properties of the transistor. Good agreement between calculation and experiment is found. The dependence of noise temperature on gate length and channel thickness is presented.     

Low frequency noise in SiGe-base heterojunction bipolar transistors and SiGe-channel metal oxide semiconductor field effect transistors

We show that low frequency noise (LFN) in SiGe-base heterojunction bipolar transistors and SiGe-channel pMOSFETs may be made significantly lower than that in their all-Si counterparts and indicate how this can be done. Optimization of LFN in SiGe channel pMOSFETs follows from a calculation involving a novel analytical model, which accounts for both static and LFN characteristics of SiGe-channel devices.     

Optimizing the fabrication process for high performance graphene field effect transistors

As an emerging material, graphene has attracted vast interest in solid-state physics, materials science, nanoelectronics and bioscience. Graphene has zero bandgap with its valence and conduction bands are cone-shaped and meet at the K points of the Brillouin zone. Due to its high intrinsic carrier mobility, large saturation velocity, and high on state current density, graphene is also considered as a promising candidate for high-frequency devices. To improve the reliability of graphene FETs, which include shifting the Dirac point voltage toward zero, increasing the channel mobility and decreasing the source/drain contact resistance, we optimized the device fabrication process. For CVD grown graphene, the film transfer and the device fabrication processes may produce interfacial states between graphene and the substrate and make graphene p or n-type, which shift the fermi level far away from the Dirac point. We have found that after graphene film transfer, an annealing process at 400 °C under N₂ ambient will shift Dirac point toward zero gate voltage. Ti/Au, Ni, and Ti/Pd/Au source/drain structures have been studied to minimize the contact resistance. According to the measured data, Ti/Pd/Au structure gives the lowest contact resistance (～500 ohm μm). By controlling the process of graphene growth, transfer and device fabrication, we have achieved graphene FETs with a field effective mobility of 16,000 cm²/V s after subtraction of contact resistance. The contact resistivity was estimated in the range of 1.1 × 10^?6 Ω cm² to 8.8 × 10^?6 Ω cm², which is close to state of the art III–V technology. The maximum transconductance was found to be 280 mS/mm at V_D = 0.5 V, which is the highest value among CVD graphene FETs published to date.     

Induced-gate thermal noise in high electron mobility transistors

The induced-gate thermal noise in high electron mobility transistors (HEMTs) is evaluated by a very general schematic and the minimum noise figure F_min?1 due to thermal noise is calculated over a wide frequency range. The results are applied to the conductance g(V) per unit length proposed by Delagebeaudeuf and Linh, and the effects of hot electrons in very short channels are indicated. The measurements of F_min by Delagebeaudeuf and Linh can be explained by taking the hot electrons effect into account. The possibility that a somewhat different expression for g(V) may be needed is left open and is easily incorporated in the general schematic of the discussion.     

A noise model for high electron mobility transistors

A model to explain the noise properties for AlGaAs/GaAs HEMT's, AlGaAs/InGaAs/GaAs pseudomorphic HEMT's (P-HEMT's) and GaAs/AlGaAs inverted HEMT's (I-HEMT's) is presented. The model Is based on a self-consistent solution of Schrodinger and Poisson's equations. The influence of the drain-source current, frequency and device parameters on the minimum noise figure F_min and minimum noise temperature T_min, for different HEMT structures are presented. The study shows that P-HEMT's have a better noise performance than the normal and inverted HEMT's. The present model predicts that a long gate P-HEMT device will exhibit a better noise performance than a conventional HEMT. There is a range of doped epilayer thickness where minimum noise figure is a minimum for pseudomorphic HEMT's which is not observed in conventional and inverted HEMT's. The calculated noise properties are compared with experimental data and the results show excellent agreement for all devices     

A process for high yield and high performance carbon nanotube field effect transistors

Carbon nanotube field effect transistors (CNTFETs) have been considered as one of the potential candidates for nanoelectronics beyond Si CMOS. However, it is not easy to have high performance CNTFETs with high yield currently. In this work, we proposed a local bottom-gate (LBG) CNTFETs combined with a novel device concept and optimized process technologies. High performance of CNTFET with low subthreshold swing of 139 mV/dec, high transconductance of 1.27 μS, and high I_on/I_off ratio of 10⁶ can be easily obtained with Ti source/drain contact after a post annealing process. Record high yield of 74% has been demonstrated. On the basis of the proposed process, lots of high performance CNTFETs can be obtained easily for advanced study on the electrical characteristics of CNTFETs in the future.     

Temperature dependence of 1/f noise in polysilicon-emitter bipolar transistors

1/f noise was measured on polysilicon-emitter bipolar n-p-n and p-n-p transistors over a temperature range of 173K相似文献   

Device reliability study of AlGaN/GaN high electron mobility transistors under high gate and channel electric fields via low frequency noise spectroscopy

A set of different short term stress conditions are applied to AlGaN/GaN high electron mobility transistors and changes in the electronic behaviour of the gate stack and channel region are investigated by simultaneous gate and drain current low frequency noise measurements. Permanent degradation of gate current noise is observed during high gate reverse bias stress which is linked to defect creation in the gate edges. In the channel region a permanent degradation of drain noise is observed after a relatively high drain voltage stress in the ON-state. This is attributed to an increase in the trap density at the AlGaN/GaN interface under the gated part of the channel. It was found that self-heating alone does not cause any permanent degradation to the channel or gate stack. OFF-state stress also does not affect the gate stack or the channel.     

Hot electron transport effects in field effect transistors

Present semiconductor devices may be placed in one of several groups according to whether hot electron effects are or are not responsible for their operation. Gunn diodes fall into the former category whereas field effect transistors are in the latter. Currently used field effect transistor materials such as gallium arsenide are however subject to electron transfer with significant negative differential mobility and device operation may be expected to reflect this contribution. We have developed a program that numerically simulates the space and time dependent effects of negative differential mobility on field effect transistor operation. We have also included the effects of the external circuit which we represent by lumped elements. We will illustrate the transient formation of high field domains within the conducting channel and conditions necessary for propagation and recycling between the gate and drain contacts. We will also display stationary space charge configurations specific to the presence of negative differential mobility.     

1/f noise in modulation-doped field effect transistors

Low frequency noise measurements are reported in modulation-doped GaAs field effect transistors. The noise spectrum is1/fand is relatively large. At a given frequency the equivalent saturated diode current Ieqvaries as V2, as expected for a fluctuating resistor, and saturates when the characteristic saturates.     

Morphology optimization for achieving air stable and high performance organic field effect transistors

To develop an all organic active matrix light emitting display required for large area thin display, electronic paper and electronic paints, Si-based thin film transistor has to be replaced with organic thin film transistor (OTFT). The most important issues in OTFT are the low charge carrier mobility and poor stability under ambient conditions, which critically depend on how organic thin films are grown on different substrates. Here we show that both these issues are correlated and can be overcome by certain surface morphology which can only be achieved through anisotropic growth. Careful control of different growth parameters can lead to unprecedented control on thin film morphology which has been shown to be engineered reversibly and reproducibly. High temperature and low evaporation rate increase the diffusive mobility of molecules, which are responsible for the stacking of molecules to higher length scales. By carefully choosing a temperature and evaporation rate, elongated rod-like grains were grown for achieving high performance and stable thin film transistors.     

Analysis of high electron mobility transistors based on a two-dimensional numerical model

A two-dimensional numerical model is employed to simulate the device performance of the high electron mobility transistor. A 1- µm gate device is analyzed using the equilibrium velocity-field characteristic of GaAs. The calculation reveals existence of electron accumulation in the GaAs layer under the drain side end of the gate electrode. A quasi-piecewise linear velocity-field characteristic is also employed to simulate the velocity overshoot effect. The cutoff frequency is found to be improved by about 50 percent owing to the velocity overshoot effect.     

Temperature dependence of n-type MOS transistors

Ionization of surface states with increasing temperature is shown to be responsible for the positive temperature coefficient of the drain current often observed inn-type silicon MOS transistors. Competition of this effect with a decrease in mobility for increasing temperature is demonstrated to yield transistors with negative, positive, or zero temperature coefficients. The reflection of surface state ionization with increasing temperature as a linear decrease in gate voltage (for constant drain current) is theoretically explained. Since this linear decrease in gate voltage is a direct function of surface state density, a new method for determining the surface state density near the conduction band is developed. For many transistors gate voltage decreased about 40 millivolts per degree centigrade increase in temperature. This corresponds to a surface state density on the order of 10¹³per square centimeter per electron volt.     

The noise performance of microwave transistors

Expressions for the noise parameters of microwave transistors are derived. The theory is based on a small-signal common-emitter equivalent circuit which includes a new basic noise equivalent circuit and the dominanting header parasitics. The theory is verified experimentally in the L-band (1 to 2 Gc/s) frequency range using Ge and Si microwave transistors. It is found that the header parasitics have little influence on the minimum noise figure, but do have large effects on the equivalent noise resistance and the optimum source admittance in the frequency region above about one-half of the series-resonant frequency resulting from the parasitics in conjunction with wafer parameters. For a quick evaluation of the noise performance, new approximate expressions are also given for the noise figure and for the optimum current which produces the lowest value.     

The temperture dependence of substrate parameters and their effecton microstrip antenna performance

In the common approach to the design of microstrip antennas, the designers rely on data provided in the manufacturers' specifications, even though such specifications are confined to standard environmental conditions. In practice, the electrical parameters of the substrates may deviate from the manufacturers' data, thus making the antenna designer adopt a deficient design strategy. In the study reported, microstrip substrates were exposed to large temperature variations and their temperature dependent properties were measured in a specialized laboratory for dielectric materials. The results include plots of the dielectric constant and dissipation factor for wide temperature ranges equivalent to those in airborne applications. On the basis of this experimental data, the substrates were divided into four categories according to their dielectric constant value and its temperature dependence. Using both manufacturers' data and the measured values, a series of microstrip dual-feed aperture-coupled patch antennas were designed for the four categories of substrates and the sensitivity of their electrical performance due to temperature variations was fully investigated