Low temperature operation of UHF power static induction transistors

This paper describes the results of recent experiments with high power surface gate static induction transistors (SITs) operated at and near liquid nitrogen temperatures. The temperature dependence of important large signal and small signal device parameters over a wide range of operating temperatures is described. UHF power performance of liquid nitrogen cooled SIT power amplifiers is described as well. At 425 MHz, a single transistor power amplifier has been fabricated which exhibits output power levels > 350 W with 8 dB gain and nearly 80% drain efficiency. Smaller test devices have been used in an 850 MHz amplifier, which exhibits 30 W c.w. with 7.8 dB gain and 64% drain efficiency.     

Impurity ionization in MOSFETs at very low temperatures

The physics of freeze-out in conventionally doped silicon is examined. A dynamic equilibrium theory, similar to that used in deep level transient spectroscopy, is developed to describe the time dependence of thermal ionization. The theory is extended to include field-dependent ionization, which accounts for impurity ionization at very low temperatures. The specific mechanisms (Poole - Frenkel ionization and tunnelling) are discussed, and the temperature and field dependences of the mechanisms are described. It is then shown that MOS capacitors and MOSFETs have very different behaviour at very low temperatures. Experimental results are examined, showing a distinct change in the behaviour of long term current transients at very low temperatures, as predicted by the model. The theoretical model developed here, when used in a simple one-dimensional simulation, agrees with substrate current measurements. Finally, some implications for very low temperature MOSFET operation are considered.     

N-channel accumulation layer MOSFET operating at 4 K

An accumulation layer n-channel MOSFET that operates at 4 K has been fabricated. Sharp hysteretic current kinks in the I–V characteristic are observed, where the transistor switches discontinuously between two well defined states. The kinks are modelled in terms of changes in the device potential configuration due to holes generated by avalanche breakdown in the high electric field region near pinch off. Noise measurements which elucidate the physical mechanisms causing the current kinks are presented.     

Device performance of p-Ge MOSFETs at liquid nitrogen temperature

The device performance of p-channel Ge MOSFETs at liquid nitrogen temperature is reported and initial results of room temperature irradiation with 2-MeV electrons on the cryogenic device performance is described. It is shown that at 77 K an increase of the drain current and g_m is observed. This increase of the g_m can be explained by considering the balance between reduced phonon scattering on the one hand and increased Coulomb scattering by interface states, on the other. After irradiation, a slight negative shift of the threshold voltage and a decrease of the drain current for input and output characteristics have been observed together with a decrease of the transconductance (g_m).     

对低温丙烯贮罐预冷操作的探讨

对低温丙烯罐的预冷工艺进行了较为仔细深入的研究,提出了较为科学、合理的预冷操作方法,确保了丙烯贮罐内罐基本维持每小时温降1℃.罐内任意两点温差不超过10℃的操作条件,对刚刚维修之后的低温丙烯贮罐起到了保障作用.     

液氦温区国际温标的转换

概括介绍液氦温区国际实用温标的发展情况,系统地给出温标T24,T29,T32,T37,TBS,T48,T55E,TL55,T58,T62,T68,T76以及目前正在采用的T90之间的转换关系,为此编写了计算机程序,可直接用于以上各温标间的数值转换.     

液氮罐内低温氮气的温度场研究

对装有少量液氮的液氮罐内的温度分布进行了系统研究,提出了相应的温度分布模型.研究表明,在10 L容积的液氮罐内注入少量液氮时,罐内温度可保持低于-130℃持续约25天,适用于多种场合的超低温保存.通过调节距离液氮面的高度,可选择保存样品的温度范围并控制样品的升降温速度.理论计算的温度分布与测量的结果符合较好,证实了所建立模型的合理性和有效性.     

AlN/玻璃复合材料的低温烧结和性能

用热压方法在850～1000℃制备出低温烧结AlN/硼硅酸盐玻璃复合材料。研究了玻璃的高温行为及其对AlN的润湿能力,分析了颗粒配比对复合材料烧结致密化的影响,探讨了影响复合材料热导率的因素。结果表明:引入对AlN润湿良好的硼硅酸盐玻璃,可将烧结温度降低到1000℃以下;采用适当的AlN和玻璃粉体的粒径比有利于提高复合材料的烧结致密化程度。具有均匀显微结构的低温烧结AlN/玻璃复合材料具有良好的导热性能,其热导率高于10W/(m·K)。     

液氮温度下JX-6型椰壳炭的性能测试

活性炭是NBI低温吸附泵吸附面的关键组成部分,其性能是决定NBI低温泵抽气性能的关键因素之一.本文选取JX-6型椰壳活性炭,用全自动比表面积及孔径分析仪(ASAP2020)在液氮温度下对其性能进行了测试,并对实验数据进行了分析.实验结果表明,该活性炭具有良好的孔隙结构和较强的吸附性能,其最大吸附量达到252 cm3/g STP.为进一步研究NBI低温泵的低温吸附抽气提供了理论依据.     

Behaviour of power MOSFETs at cryogenic temperatures

In this paper an investigation is reported on Siemens-power-metal-oxide-semiconductor (SIPMOS) transistors of both p and n channel types, for their suitability for cryogenic applications. The drain characteristics, temperature dependence of R_ds(on) and switching behaviour have been studied in the temperature range 4.2 – 300 K in BSS91 and BSS92 MOSFETs. The experiments reveal that these types of power transistors are well suited for operations down to ≈ 30 K. However, below 30 K the operating characteristics make them unsuitable for application. This arises because of carrier freeze-out in the n⁻ region on the substrate, which forms a drain.     

Eight channel pressure measuring system for cryogenic use in the European Transonic Wind-tunnel over the temperature range 78 – 300 K

After three years' development of cold-electronic systems at the University of Southampton, a prototype eight channel (four pressure, four temperature) computer controlled data logger with 16 bit A/D converter and optical fibre lead-out has been constructed, all operating at temperatures between 300 and 78 K with a precision of +0.05%.     

非真空条件下柔性多层材料高低温绝热性能实验测量

制作了柔性绝热被,设计和搭建了高温、低温环境测试系统,通过测量多层绝热被内外两侧及外侧附近空气的温度变化,衡量不同配置下多个多层绝热被样品的综合绝热性能。考察了厚度、多层配置方式、气密性等对柔性多层材料在常压下的高低温隔热作用和符合-100℃至+135℃高低温环境应用的柔性多层绝热被的最佳厚度及配置方式。     

高压低温制备硅材料的性能研究

研究了用高压低温法制备的硅材料的性能。进行了不同的温度条件下制备陶瓷硅材料的实验研究．获得了最佳的制备条件。用XRD分析了材料的物相;阿基米德法测量了制备材料的密度;对材料的电阻率和硬度进行了测量。结果表明：用高压低温方法可以制备出无氧化相存在的陶瓷硅材料,其最佳的烧结温度为600℃;样品具有较好的机械强度和硬度,获得了适于制备多晶硅薄膜的衬底材料。     

基于液氦温区测试高真空多层绝热性能的量热器设计

设计了一个用于测试液氦温区的多层绝热材料的量热器平台,对量热器进行了结构设计、力学分析和理论漏热计算以验证平台可靠性。力学分析的结果表明,量热器最大的位移变形量为0.16 mm,位于下保护胆底部封头;应力最大为49 MPa,位于液氮冷屏的顶部封头处。理论漏热计算的结果表明,当稳定测试时间为8 h时,所设计的容器容量均满足需求。基于力学分析和理论漏热计算的结果,得知所设计的量热器满足测试多层绝热性能的要求。     

磁控溅射低温制备ZnO:Al透明导电薄膜的正交设计

采用锌铝(2%(质量分数))合金靶,保持真空腔在50℃低温下,结合正交试验表,运用直流反应磁控溅射法制得ZnO∶Al(ZAO)薄膜.通过分光光度计、半导体霍尔效应测试等手段对薄膜各项性能进行了表征.通过正交分析法对所得样品相关特征指标进行分析,在少量的9组实验下,得到溅射功率、时间、靶基距和氧流量百分比4个独立工艺参数对薄膜特性影响的同时,得出直流反应磁控溅射法制备ZAO薄膜的最优组合工艺为:溅射时间20min,靶基距6cm,溅射功率80W,氧流量百分比7%;对应样品的Фic值达4.1050×10-2/Ω,电阻率为3.9×10-4Ω·cm,载流子浓度达1.09×1021/cm3.     

范德瓦尔斯氮气的低温热力学性质研究

采用热力学方法,根据实验测得的氮气的维里系数,导出了氮气的范德瓦尔斯系数a、b.结果表明,实验方法得到的范德瓦尔斯系数与临界参数(Vc,Tc,Pc)确定的范德瓦尔斯系数有明显差异,在低温(90 K-250 K)区,范德瓦尔斯系数随温度改变有显著变化,这些变化对低温氮气的状态方程和热容量等重要热力学性质的影响是显著的.如果不考虑这些变化,可能导致不合理的错误结果.     

国产石墨薄膜低温导热系数测量

在90-350K温度范围内,设计了1套实验装置,用以测量一种国产石墨薄膜的导热系数.介绍了实验装置的结构和原理,以及相关的数据处理方法.最终利用该装置得出了石墨薄膜导热系数与温度的关系.结果表明,该石墨薄膜在低温下可以作为铜的理想替代材料.     

冷绝缘高温超导电缆用绝缘材料PPLP在液氮中拉伸状态下的冲击绝缘击穿强度

对聚丙烯复合纤维纸(PPLP)在液氮中拉伸状态下的冲击绝缘击穿强度进行了实验研究,用韦伯概率分布的方法进行数据处理,得出不同拉伸应力下0.1%击穿概率的冲击绝缘击穿强度。根据实验结果,结合相关的设计方法,对110 kV冷绝缘高温超导电缆本体用PPLP绕包时的绕包厚度和绕包层数进行了设计。     

一种可用于材料在低温环境下放气的测试系统

总结了材料放气测试的各种方法：压力上升率法、收集法、称重法和气体流量法。开发了一种基于气体流量法的新法,不仅可以用于常温和较高温度,而且可以用于材料在低温环境下放气的测试,最低测试温度可以达到100K左右。此系统方便实用,具备较高的测试精度。     

低温青藏高原土壤中镁合金阳极的电化学性能

为评价低温土壤对镁合金阳极电化学性能的影响,通过极化曲线、交流阻抗和电流效率实验方法,研究了4种镁合金阳极在-4℃和4℃的模拟低温青藏高原土壤中的电化学性能.研究表明:镁合金中加入Mn、Al和Zn元素可与杂质元素形成阴极作用较弱的金属间化合物,降低了镁合金的自溶解倾向,提高了电流效率;镁合金阳极在低温青藏高原土壤中呈活性溶解状态,溶解活性和反应活性由强到弱顺序为MGAZ63B镁合金、MGAZ31B镁合金、MGM1C镁合金和高纯镁;4种镁合金阳极中MGAZ63B的电流效率最高,-4℃和4℃时分别为54.39%和61.77%;4℃土壤中氧的扩散速率比-4℃时高,故镁合金阳极在青藏高原土壤中4℃时溶解活性和电流效率均优于-4℃时.