Microwave performance of pseudomorphic resonant-tunnelling hot electron transistors at 77 K

Describes the first 77 K microwave measurements for resonant-tunnelling hot electron transistors (RHETs) fabricated using GaInAs/AlInAs pseudomorphic heterostructures. A collector current peak-to-valley ratio of 10 is obtained with a peak collector current density of 2*10/sup 5/ A/cm/sup 2/. A current gain cut-off frequency f/sub T/ of 63 GHz and a maximum oscillation frequency f/sub max/ of 44 GHz are measured at 77 K with an emitter current density of 1.1*10/sup 5/ A/cm/sup 2/.<>     

MOS device modeling at 77 K

The state of the art in self-consistent numerical low-temperature MOS modeling is reviewed. The physical assumptions that are required to describe carrier transport at low ambient temperatures are discussed. Particular emphasis is placed on the models for space charge (impurity freeze-out), carrier mobility (temperature dependence of scattering mechanisms at a semiconductor-insulator interface), and carrier generation-recombination (impact ionization). The differences with regard to the numerical methods required for the solution of low-temperature models compared to room-temperature models are explained. Typical results obtained with the simulator MINIMOS 4 are presented. These include comparisons of short-channel effects and hot-electron phenomena such as energy relaxation and avalanche breakdown at 77 K and 300 K ambient temperatures     

Miniaturization of Si MOSFET's at 77 K

Micrometer and submicrometer dimension Si MOSFET's have been studied at liquid nitrogen temperature. The emphasis of the study has been on the changes in the minimum channel length required for long-channel behavior Lmindue to cooling. It is found that there is a reduction in Lminwhich is quite considerable in MOSFET's with low-channel doping. We have shown that this effect is due to a shorter lateral depletion width, and therefore longer effective channel length at low temperatures. A drastic decrease in punchthrough current has also been observed.     

可工作于77 K低温下的CMOS缓冲器

设计了用于制冷型红外读出电路系统的输出缓冲器,该缓冲器能在读出电路5 MHz的读出速度下驱动约20 pF的电容,可以在低温77 K下工作。对运放的增益,频率特性等进行了详细地阐述,并考虑了低温77 K时MOSFET参数的变化带来的影响。最后,给出了修改CMOS常温模型参数后的仿真结果,芯片采用0.35μm,3.3 V CMOS工艺实现,并给出了77 K下的测试结果,满足红外读出电路系统要求。     

Theory of rf SQUIDS operating at 77 K

A comprehensive analytical theory of nonhysteretic rf SQUIDs operating in the adiabatic mode at elevated temperatures, around and above 77 K, is presented. When β≪1 (β is the hysteresis parameter) the theory is applicable also for rf SQUIDs operating in the nonadiabatic mode. In contrast to previous theories which are applicable only if βΓ≪1 (the case of small thermal fluctuations — 4 K), where Γ is the noise parameter, the present theory is valid for βΓ around unity or higher (the case of high thermal fluctuations, 77 K). A good qualitatively agreement with experimental data has been found. Based on this analytical investigation, the superiority at 77 K of rf SQUID over its counterpart, the dc SQUID, is theoretically predicted.     

77K下工作的双层多晶硅发射区RCA器件和电路

研究了掺磷双层多晶硅RCA器件和电路的制备工艺及其温度特性.在工艺中采用自对准双极结构,生长一层RCA超薄氧化层,并用快速热退火处理RCA氧化层.研制的多晶硅发射区RCA晶体管不仅具有较低的电流增益-温度依赖关系,而且还具有较快的工作速度.首次制备出多晶硅发射区RCA ECL静态二分频器在室温下其工作频率为1.1-1.2GHz,在液氮温度下能够正常工作,工作频率可达730MHz.     

77K下工作的双层多晶硅发射区RCA器件和电路

研究了掺磷双层多晶硅 RCA器件和电路的制备工艺及其温度特性 .在工艺中采用自对准双极结构 ,生长一层 RCA超薄氧化层 ,并用快速热退火处理 RCA氧化层 .研制的多晶硅发射区 RCA晶体管不仅具有较低的电流增益 -温度依赖关系 ,而且还具有较快的工作速度 .首次制备出多晶硅发射区 RCA ECL静态二分频器在室温下其工作频率为 1.1— 1.2 GHz,在液氮温度下能够正常工作 ,工作频率可达 730 MHz.     

Low- and high-temperature superconducting microwave filters

Stripline and microstrip filters at X-band were designed and fabricated using low- and high-temperature superconductors in quarter-wave, parallel-coupled section configurations. Low-temperature superconducting niobium thin films, deposited on single-crystal sapphire, were used to build to six-pole stripline filters with adjacent passbands and approximately 3 dB crossovers and 1.2% bandwidth. Four- and six-pole microstrip filters were made with in situ epitaxial YBa₂Cu₃O₇ (YBCO) films on LaAlO₃ substrates. All the YBCO filters showed 77 K passbands with clean skirts and high out-of-band rejection. The six-pole filters had adjacent passbands with -28 dB crossovers and 1.5% bandwidth     

DIBL in short-channel NMOS devices at 77 K

Detailed experimental and two-dimensional numerical simulation results on drain-induced barrier lowering (DIBL) versus channel length at 300 and 77 K in short-channel NMOS devices are presented. It is found that by decreasing the temperature from 300 to 77 K. DIBL in NMOS devices with effective channel lengths (L) from 0.5 to 2.0 μm is improved for the range of L<0.6 μm and L>1.2 μm, but is worse for L between 0.6 and 1.2 μm. The new version of the two-dimensional device numerical simulation program MINIMOS 4.0, which includes device modeling at cryogenic temperatures, was used to investigate this unique characteristic. The measured DIBL characteristics can be explained physically as the transition from surface DIBL through the subsurface DIBL to the bulk DIBL or punchthrough effect at 300 K, but almost a surface DIBL for the whole range of channel length variation at 77 K. Design considerations for the channel doping profile for low-temperature operation based on keeping the same DIBL and V_TH as required for room-temperature operation are briefly discussed     

Switching characteristics of scaled CMOS circuits at 77 K

Performance enhancement of CMOS inverters at room and liquid-nitrogen temperatures are studied. The extent of delay improvement at low temperature is limited by the velocity saturation effect, as the channel lengths are decreased and/or the supply voltage increased. An analytical delay model taking into account velocity saturation is developed that accurately predicts the measured delay of CMOS inverter chains with drawn channel lengths down to 0.5 µm, Compared are the relative merits of CMOS devices operating at 77 K and those scaled for room-temperature operations.     

InAs/GaSb infrared photovoltaic detector at 77 K

The characterisation of an 8 μm infrared photovoltaic detector based on InAs/GaSb superlattices is carried out at 77 K for the first time. The built-in field is established by the Fermi level difference between the superlattice surface and the InAs buffer layer. The photocurrent is from photoexcited carriers traversing through the superlattice conduction miniband. A current responsivity of 0.07 A/W has been obtained, implying that one out of 10 photoexcited electrons has been collected     

50-Å gate-Oxide MOSFET's at 77 K

While hot-carrier-induced degradation is aggravated at cryogenic temperature, a very thin gate-oxide (52-Å) device can still tolerate a 3-V power-supply voltage at 77 K. Hot-carrier-induced degradation may not be the limiting factor in choosing the power-supply voltage and special drain structures may be necessary for very thin gate MOSFET's even at 77 K. However, mobility reduction at high VGis more severe both at lower temperatures and for thinner oxides. Electron mobility appears to be oxide-thickness-dependent at 77 K. The dependence of the electron mobility on the normal field is so strong that it results in unusual I-V characteristics such as negative transconductance at 77 K for an oxide field above 3 MV/cm. The I--V characteristics have been modeled with a mobility dependence on VGSof the form µn ∞ (1 + η(VGS- Vt/Tox)²+ (E/Ec))^-1for 52-Å devices.     

High-field microwave incremental conductivity of cadmium selenide at 77 K

The microwave conductivity of cadmium selenide has been calculated at 77 K assuming a displaced Maxwellian energy distribution function for the electrons. It is found that the microwave conductivity decreases monotonically with the applied electric field and has a lower value for higher impurity concentration. The frequency dependence of the microwave conductivity shows that it is substantially constant up to the millimeter wavelength range of frequencies.     

Compact superconducting coplanar meander line filters

Novel slow-wave coplanar waveguide (CPW) filters using high temperature superconductor (HTS) films are presented. Both half-wavelength and quarter-wavelength resonators are used in the filter topology. The miniaturisation is achieved using meander structure and interdigital grounding lines. A 3-pole Chebyshev bandpass filter has been designed, fabricated and studied. The untuned experimental results are in very good agreement with the simulated responses.     

MOSFET behavior and circuit considerations for analog applications at 77 K

We present an investigation into the behavior of silicon MOS transistors and analog circuits operated at liquid-nitrogen temperature (LNT). Simple scaling rules are used to predict the LNT performance of CMOS operational amplifier circuits designed for room-temperature operation. Measurements show that unity gain frequency and slew rate can be improved by the same amount as the mobility increase with no loss of stability if bias currents are properly controlled. We also show that room-temperature CMOS amplifier circuits can be redesigned for 77-K operation by reducing channel widths and compensation capacitor area, giving performance equal in most respects to that of unscaled circuits at room temperature. However, 1/f noise is degraded by such redesign. Similar considerations of NMOS amplifiers show that such circuits do not benefit greatly from operation at liquid-nitrogen temperature. To aid in studying the temperature dependence of the sheet resistance of diffused resistors, a computer program was developed based on available models for bulk mobility and carrier freeze-out. Accurate predictions require a temperature dependence for lattice scattering that differs from previously reported values.     

Generation-recombination noise at 77°K in silicon bars and JFETs

The theory of generation-recombination noise in silicon bars and in JFETs is extended to the case in which the devices operate in the hot electron regime. It is shown that Nougier et al.'s measurements at 77°K can at least be partly explained as generation recombination noise; as a matter of fact, the theory can provide an almost perfect match for field strengths between 1000 and 3000 V/cm for g-r noise alone. We believe, however, that some hot electron noise with a similar field dependence as g-r noise is present. One can now understand why Kim, van der Ziel and Rucker found an activation energy of only 63 mV for the noise in silicon JFETs around 77°K.     

Spontaneous and stimulated UV luminescence of ZnO:N at 77 K

The spontaneous and stimulated UV luminescence spectra of ZnO:N samples possessing different nitrogen contents are measured at a temperature of 77 K. Luminescence peaks resulting from bound and free excitons, biexcitons, and electron recombination via the nitrogen acceptor level are identified. The optical depth (123 meV) of the N_O impurity acceptor level is determined. It is established that stimulated UV luminescence originating from inelastic exciton interaction sets in as the optical pump power increases.     

Hot-electron-induced interface state generation in n-channel MOSFET's at 77 K

Hot-electron-induced degradation in n-channel Si MOSFET's as a result of stress voltages applied at 77 K was studied. The devices were stressed at 77 K for 48 h with a drain voltage of 5 V and a gate voltage corresponding to that at which maximum substrate current was measured. Comparison of pre-stress and post-stress electrical characteristics for forward and for inverse mode operation at room temperature and at 77 K indicate that the observed degradation was due to the generation of hot-electron-induced acceptor interface states at the drain end of the device approximately 0.09 eV below the Si conduction band edge. No trapped charge resulting from hot-electron injection into the gate oxide was observed. The charge associated with the filled interface states had no observable effect on effective channel electron mobility at room temperature, and reduced that at 77 K by no more than 25 percent of the pre-stress value. Operation of CMOS inverters in either logic state (OFF, ON) resulted in no degradation of either device. Operation in a switching mode at 77 K did result in degradation of the n-channel device but not the p-channel FET. The observed degradation is thought to be correlated with the substrate current generated during the switching transient.     

77K MOSFET计算机模拟增量限制方法

对低温器件计算机模拟方法作了具体的考虑。从求解变量和半导体物理意义出发，数值计算结果事先有一个定性范围，如果每一次循环的迭代初值都修正到这个数值范围内，那么选代过程将以更快的速度接近真解。提出了适用于低温半导体器件计算机模拟的增量限制方法，并且将该方法插入ＭＩＮＩＭＯＳ４．０进行了数值实验。结果表明，设置增量限制能保证低温半导体器件模拟的数值收敛性，并巨有较快的收敛速度。