Effects of ionizing radiation on oxidized silicon surfaces and planar devices

This paper examines in detail the effects of high and low energy electron, X-ray, and ultraviolet radiation on oxidized silicon surfaces and planar devices. Two permanent effects of ionizing radiation on oxidized silicon surfaces are distinguished: 1) The buildup of a positive space charge within the oxide, and 2) The creation of fast surface states at the oxide-silicon interface resulting in increased surface recombination velocity. The dependence of these effects on dose and dose rate, on bias applied during irradiation, and on structural parameters is discussed and a theory is presented which accounts for the observed features of the space-charge buildup. This theory involves trapping of holes which are generated within the oxide by the radiation. It is shown that all details of the experimental observations can be accounted for by assuming a high density of hole traps near the oxide-silicon interface which decays rapidly with distance into the oxide. Radiation-induced changes in the characteristics of MOS and junction field-effect transistors, p-n junction diodes, and p-n-p and n-p-n transistors are reported and examined in terms of the above two effects. It is shown that the charge buildup causes shifts in the operating point of MOS transistors, catastrophic increases in the reverse current of p-n junctions, and variations in their breakdown voltage. The increase in fast surface-state density is responsible for the lowering of the transconductance of MOS transistors and, in combination with the space-charge buildup, for the degradation of the current gain in bipolar transistors. It is shown that junction field-effect transistors are relatively insensitive to both effects of ionizing radiation and therefore offer the most promise for use in ionizing radiation environments.     

Total ionizing dose radiation effects on NMOS parasitic transistors in advanced bulk CMOS technology devices

In this paper, total ionizing dose effect of NMOS transistors in advanced CMOS technology are examined. The radiation tests are performed at ⁶⁰Co sources at the dose rate of 50 rad (Si)/s. The investigation''s results show that the radiation-induced charge buildup in the gate oxide can be ignored, and the field oxide isolation structure is the main total dose problem. The total ionizing dose (TID) radiation effects of field oxide parasitic transistors are studied in detail. An analytical model of radiation defect charge induced by TID damage in field oxide is established. The I-V characteristics of the NMOS parasitic transistors at different doses are modeled by using a surface potential method. The modeling method is verified by the experimental I-V characteristics of 180 nm commercial NMOS device induced by TID radiation at different doses. The model results are in good agreement with the radiation experimental results, which shows the analytical model can accurately predict the radiation response characteristics of advanced bulk CMOS technology device.     

Optically induced backgating transients in GaAs FET's

Long-term current transients have been induced with optical pulses in depletion-mode GaAs field-effect transistors (FET's). The millisecond-to-second duration and the bias dependence of the transients are similar to substrate trapping and backgating events initiated by ionizing radiation. A specific region of a FET-the semiconductor region adjacent to the connecting strip between the gate electrode and the gate bonding pad-is particularly sensitive to optical backgating. In this region low-incident optical energies produce a positive current transient; but when the optical intensity exceeds ∼1 mJ/cm², a transient decrease in current is observed. Optical studies promise to be a simple and convenient means of simulating many of the effects of ionizing radiation.     

Laser-assisted simulation of transient radiation effects in heterostructure components based on A<Superscript>III</Superscript>B<Superscript>V</Superscript> semiconductor compounds

The possibility of the simulation of transient radiation effects using laser radiation in microwave heterostructure elements based on A^IIIB^V semiconductor compounds is studied. The results of the laser simulation of transient radiation effects in pseudomorphous high-electron mobility transistors (pHEMTs) based on AlGaAs/InGaAs/GaAs heterostructures are reported. It is shown that, for the adequate simulation of transient effects in devices on GaAs substrates, one should use laser radiation with a wavelength of λ = 880–900 nm taking into account the dominant mechanisms of ionization in the transistor regions.     

Optimization of the parameters of HEMT GaN/AlN/AlGaN heterostructures for microwave transistors using numerical simulation

The numerical simulation, and theoretical and experimental optimization of field-effect microwave high-electron-mobility transistors (HEMTs) based on GaN/AlN/AlGaN heterostructures are performed. The results of the study showed that the optimal thicknesses and compositions of the heterostructure layers, allowing high microwave power implementation, are in relatively narrow ranges. It is shown that numerical simulation can be efficiently applied to the development of microwave HEMTs, taking into account basic physical phenomena and features of actual device structures.     

Study of the effect of the gate region parameters on static characteristics of microwave field-effect transistors based on pseudomorphic AlGaAs-InGaAs-GaAs heterostructures

The results of numerical simulation and experimental study of the effect of the gate region parameters on static characteristics of microwave field-effect transistors based on pseudomorphic AlGaAs-InGaAs-GaAs heterostructures (p-HEMT) are considered. The possibility of correct simulation of static characteristics of actual device structures of p-HEMT transistors using the TCAD software package (SILVACO Inc.) is demonstrated. The essential necessity of using selective gate-groove etching to achieve controllable and reproducible device parameters is shown.     

Microwave-signal generation in a planar Gunn diode with radiation exposure taken into account

Microwave-signal generation in planar Gunn diodes with a two-dimensional electron gas, in which we previously studied steady-state electron transport, is theoretically studied. The applicability of a control electrode similar to a field-effect transistor gate to control the parameters of the output diode microwave signal is considered. The results of physical-topological modeling of semiconductor structures with different diode active-region structures, i.e., without a quantum well, with one and two quantum wells separated by a potential barrier, are compared. The calculated results are compared with our previous experimental data on recording Gunn generation in a Schottky-gate field-effect transistor. It is theoretically and experimentally shown that the power of the signal generated by the planar Gunn diode with a quantum well and a control electrode is sufficient to implement monolithic integrated circuits of different functionalities. It is theoretically and experimentally shown that the use of a control electrode on account of the introduction of corrective feedback allows a significant increase in the radiation resistance of a microwave generator with Schottky-gate field-effect transistors.     

Microwave field-effect transistors based on group-III nitrides

A concept for the design of experimental AlGaN/GaN/AlGaN double heterostructures with a two-dimensional electron channel are discussed, together with their main properties. The structures were formed by ammonia molecular-beam epitaxy on sapphire substrates. The foundations for postgrowth technology are developed for microwave field-effect transistors based on Group-III nitrides, including the formation of a mesa isolation and the preparation stage of nonrectifying contacts and the Schottky barrier. The first field-effect transistors fabricated based on the above heterostructures have a complete set of static characteristics and can operate in a mode of weak microwave signals at a frequency of 8.15 GHz.     

电离辐射前后双极型晶体管统计特性

双极型晶体管性能统计分布在电离辐射之后会发生变化,从辐射前对称的正态分布转化为辐射后非对称的对数正态分布,这一统计特性转化缺乏清晰的物理图像。为了从微观机理层次解释这一转化过程,通过大样本定制晶体管电离辐射效应实验,获得基极电流、界面陷阱电荷辐射前后的统计特性,发现两者统计特性转化具有一致性。基于基极电流的解析物理模型分析发现辐射前后基极电流统计特性转化源自于界面陷阱电荷统计特性转化,并基于中心极限定理给出了界面陷阱电荷辐射前后统计特性转化的物理解释,即界面缺陷面密度的分散性转化源于多个随机变量以乘积形式实现界面缺陷物理过程。     

Synchronization and combining of the radiation powers of active microwave antennas integrated with field-effect transistors

Combining of the powers of microwave generators designed as a array of log-periodic antennas on a dielectric substrate and field-effect transistors as active components is experimentally investigated. Possibilities of a substantial increase in the generation efficiency due to mutual synchronization of radiators are demonstrated, and conditions for formation of the radiation pattern are studied.     

On the intrinsic limits of pentacene field-effect transistors

Performance limits for pentacene based field-effect transistors are investigated using single- and polycrystalline devices. Whereas the charge transport in single crystalline devices is band-like with mobilities up to 10⁵ cm²/V s at low temperatures, temperature-independent or thermally activated charge transport can be observed in polycrystalline thin film transistors depending on the growth conditions. Trapping and grain boundary effects significantly influence the temperature dependence of the field-effect mobility. Furthermore, the device performance of p-channel transistors (mobility, on/off ratio, sub-threshold swing) decreases slightly with increasing trap densities. However, the formation of an electron accumulation layer (n-channel) is significantly stronger affected by trapping processes in the thin film devices. Single crystalline p-channel devices exhibit at room temperature mobilities as high as 3.2 cm²/V s, on/off-ratios exceeding 10⁹, and sub-threshold swings as low as 60 mV/decade. Slightly diminished values are obtained for transistors working as n-channel devices (2 cm²/V s, 10⁸, and 150 mV/decade).     

Simulation of Nonlinear Microwave FET Performance Using a Quasi-Static Model

A technique is described for accurately predicting nonlinear performance of microwave GaAs field-effect transistors in arbitrary circuit embedding. The approach is based on a quasi-static device model which is derived from measured bias and frequency dependence of the small-signal device S parameters. Excellent agreement is demonstrated between experimental and predicted "load-pull" characteristics at X band.     

The effect of dislocations formed during growth on the structure and photoluminescence of i-n −-n-n +-GaAs epilayers and on the related microwave transistors parameters

The structure of two types of GaAs i-n ^?-n-n ⁺ epilayers on GaAs〈100〉 semi-insulating substrates was studied by electron microscopy. The low-temperature photoluminescence spectra were measured and their special features were analyzed. It is shown that the formation of dislocations during growth in such structures significantly affects the photoluminescence spectra and impairs the parameters of microwave field-effect transistors based on these structures.     

Radiation effects in transit-time microwave diodes

There has been considerable progress in the direct generation of microwave power using two-terminal semiconductor devices during the last decade. Permanent and transient radiation effects on bulk (Gunn and LSA) and junction (IMPATT, TRAPATT, and BARITT) transit-time microwave diodes are reviewed. Emphasis is placed upon relating the primary effects of radiation to the physics of device operation. The principal permanent damage is attributed to carrier removal effects, impairing the RF performance of bulk diodes below 10¹⁴neutrons/cm²and junction transit-time diodes at fluences near 10¹⁵neutrons/cm². The principal transient effect is the generation of free carriers by ionizing radiation, affecting the RF performance of bulk diodes above 10⁹rad/s and junction transit-time diodes at dose rates near 10⁸rad/s.     

Radiation-induced leakage currents in n-channel Silicon-on-sapphire MOST's

This paper describes an experimental study of the source-to-drain leakage currents in silicon-on-sapphire n-channel MOS transistors before and after exposure to ionizing radiation. The leakage currents are studied as a function of device geometry and various processing parameters. The effects on the leakage currents of wet and dry gate oxidations, the transistor channel length, and optical (UV) bleaching are described. A model of hole traps in the Al2O3is proposed to explain the radiation-induced leakage currents.     

Theoretical and experimental studies of the current–voltage and capacitance–voltage of HEMT structures and field-effect transistors

The sensitivity of classical n ⁺/n ^– GaAs and AlGaN/GaN structures with a 2D electron gas (HEMT) and field-effect transistors based on these structures to γ-neutron exposure is studied. The levels of their radiation hardness were determined. A method for experimental study of the structures on the basis of a differential analysis of their current–voltage characteristics is developed. This method makes it possible to determine the structure of the layers in which radiation-induced defects accumulate. A procedure taking into account changes in the plate area of the experimentally measured barrier-contact capacitance associated with the emergence of clusters of radiation-induced defects that form dielectric inclusions in the 2D-electron-gas layer is presented for the first time.     

Anomalous nanosecond transient component in a GaAs MODFETtechnology

Modulation-doped field-effect transistors (MODFETs) exhibit transient responses that contain a variety of time constants. The strongest transients observed in the microsecond range are known to be caused by the DX centers. MODFETs also suffer a transient that arises from a source different from that of the DX centers. Preliminary measured characteristics of the nanosecond transient are presented, its effects on circuit performance are described, and its possible origin is inferred     

Electromagnetic energy and food processing

The use of electromagnetic energy in food processing is reviewed with respect to food safety, nutritional quality, and organoleptic quality. The effects of nonionizing radiation sources such as microwave and radio-frequency energy and ionizing radiation sources, e.g. radioactive cobalt-60 and caesium-137, on the inactivation of microbes and nutrients are compared with those of conventional heating processes both in terms of their kinetic behavior and their mechanisms of interaction with foods. The kinetics of microwave and conventional thermal inactivation are considered for a generalized nth-order model based on time and temperature conditions. However, thermal inactivation effects are often modeled by 1st-order kinetics. Microbial and nutrient inactivation by ionizing sources are considered for a 1st-order model based on radiation dose. Both thermal and radiation resistance concepts are reviewed and some typical values of radiation resistance are given for sensitive vegetative bacterial cells, yeasts, and molds and for resistant bacterial spores and viruses. Nonionizing microwave energy sources are increasingly used in home and industrial food processing and are well-accepted by the American public. But, despite recent Food and Drug Administration approval of low and intermediate ionizing radiation dose levels for grains and other plants products and the fact that irradiated foods are sold in more than 20 countries of the world, public fears in the U.S. about nuclear energy may limit the role of ionizing radiation in food processing and preservation and may also limit the use of nuclear fuels as an alternate source of electrical energy.     

Bias-dependent hybrid PKI empirical–neural model of microwave FETs

Empirical models of microwave transistors based on an equivalent circuit are valid for only one bias point. Bias-dependent analysis requires repeated extractions of the model parameters for each bias point. In order to make model bias-dependent, a new hybrid empirical–neural model of microwave field-effect transistors is proposed in this article. The model is a combination of an equivalent circuit model including noise developed for one bias point and two prior knowledge input artificial neural networks (PKI ANNs) aimed at introducing bias dependency of scattering (S) and noise parameters, respectively. The prior knowledge of the proposed ANNs involves the values of the S- and noise parameters obtained by the empirical model. The proposed hybrid model is valid in the whole range of bias conditions. Moreover, the proposed model provides better accuracy than the empirical model, which is illustrated by an appropriate modelling example of a pseudomorphic high-electron mobility transistor device.