紧凑型激光微水传感器的设计与研究北大核心CSCD

设计研究了一种基于可调谐激光吸收光谱技术的微量水蒸气浓度检测传感器,内置有红外激光器、气体池、探测器、温压传感器、电路板等模块,传感器外形尺寸3 cm×3 cm×20 cm。选用水蒸气在近红外v_(2)+v_(3)谱带内1368.6 nm附近吸收线为待测谱线,结合软件锁相和SG滤波技术,实现对水蒸气的快速、准确测量。搭建了微量水蒸气浓度发生装置及校准测试实验系统,以高精度镜面露点仪为标准表进行校准测试,结果表明,传感器对水蒸气体积比浓度的测量范围达0~2000 ppm,与标准表相比较的相对测量误差在-5.53%~1.84%之间,系统的最小检出限达10 ppm,响应时间小于7 s。该传感器性能指标满足在高压开关、氢冷发电、化工、制药等多个行业对湿度检测的要求,相比于传统湿度检测方法,具有测量准确度高、速度快、结构紧凑等优点,可为相关行业发展提供重要技术手段。     

Pd掺杂SnO2厚膜CO2气体传感器的制备及其气敏特性研究

当前CO_2的过度排放引发了一系列的环境问题,CO_2的检测技术成为气体传感器研究领域的热点。半导体气敏传感器是气体传感器研究的主流方向之一,其中丝网印刷法是制备厚膜传感器的最常见的方法。本文采用纳米SnO_2作为主要的气敏材料,制备了不同Pd掺杂含量的SnO_2浆料,然后采用丝网印刷法制备了SnO_2厚膜CO_2气体传感器。研究发现,当Pd的含量为SnO_2的1%(质量分数)时,传感器在258℃工作温度下,对CO_2有最大的响应值1.98。该传感器能够检测的CO_2浓度下限为1000ppm,其响应值随着CO_2浓度的升高而增大。     

长寿命CO_2激光器

实验证明,要获得长寿命的 CO_2激光器的主要措施有:(1)杜绝慢性漏气;(2)电极材料的选择及氧化处理;(3)减少 CO_2:分子的分解。我们的做法是:激光管不经烘烤,并附加水蒸气,电极材料均经真空除气且充氧氧化,在采用纯银电极、气体组分分别为(1)CO_2-N_2-He-Xe-H_2O;(2)CO_2-CO-He-Xe-H_2O;(3)CO_2-N_2-CO-tte-Xo-H_2O 时,运转寿命分别达(1)10476小时;(2)9185小时(仍在运转);(3)9207小时(仍在运转)。而采用纯镍电极,气体组分为 CO_2-N_2-He-Xe-H_2O,运转寿命达1644小时。     

复合碳酸盐作为二氧化碳电化学传感器的敏感电极

利用碳酸锂-锂钡掺杂氧化碳酸盐所形成的复合物作为敏感电极材料,YSZ作为固体电解质,构建二氧化碳电化学传感器,并通过扫描电镜、XRD、二氧化碳响应等方法,对不同原料配比的传感器性能进行了研究。结果表明,基于碳酸锂-锂钡掺杂氧化碳酸盐的YSZ二氧化碳电化学传感器具有快速和准确的电动势响应,其电子转移数近似为2;随着测试温度的升高,所制传感器对待测气体中CO_2浓度变化的电动势响应更快,稳定状态更好;随着敏感电极中锂钡掺杂氧化碳酸盐量的增加,传感器在350℃下的最高CO_2响应浓度降低,但在400℃时的稳定响应特性变好。     

基于La0.7Sr0.3FeO3的微结构乙醇气体传感器的研制

以La_0.7Sr_0.3FeO₃为敏感材料，设计制成了一种新型的共平面结构气体传感器.基于有限元分析软件Ansys对该传感器结构进行了优化设计.实验测得该传感器对于500ppm浓度乙醇气体的灵敏度为8.0，功耗为261mW，是同种敏感材料烧结型传感器功耗的2/3，响应时间约为1.5s，恢复时间约为2.5s，是一种功耗低、灵敏度高、稳定性好的微结构乙醇气体传感器.     

高灵敏的酞菁铜薄膜NO_2气体传感器

本文采用真空气相物理沉积技术,在平面叉指电极上沉积酞菁铜薄膜制成的气体传感器。该传感器对NO_2有很高的灵敏度和良好的选择性,能检测出空气中1ppm浓度的NO_2,响应时间几十秒、恢复时间几分钟。在320℃下进行退火处理,传感器的稳定性和重复性有明显的改善。     

钌酸铋、铱酸铋厚膜电阻材料

当配比Bi_2Ru_2O_7/玻璃从15/85变化到70/30,850℃烧结后,方阻从1.60MQ/□变到6.28Ω/□,TCR从-60ppm/℃变到200ppm/℃。当配比Bi_2Ir_2O_7/玻璃从20/80变到70/30,780℃烧结,方阻从1.1MΩ/□变到77.9Ω/□,TCR从-274ppm/℃变到269ppm/℃。高温(950℃)煅烧制得的Bi_2Ru_2O_7、Bi_2Ir_2O_7与低温(600℃、700℃)制得的相比,方阻高,TCR较负,前者宜作高电阻膜,后者宜作低电阻膜。掺入Al_2O_3、SiO_2使方阻增大,而TCR和噪声良好,TiO_2使TCR较负。Au粉使方阻急降,但改善TCR。Pt粉对方阻和TCR无明显影响。Bi_2O_3或MnO_2使TCR由正值偏向负值方向。150℃、1000小时热存放后,Bi_2Ru_2O_7低阻变化较大,高阻变化率为±1％;Bi_2Ir_2O_7阻值变化率小于0.8％。Bi_2Ir_2O_7与Bi_2Ru_2O_7相比,噪声低,TCR略大。     

基于中红外DFB-ICL的氨气传感器设计

氨气是主要恶臭物质之一,为了实现工业环境污染源中氨气排放的连续监测,研制了中红外激光气体传感器,与传统近红外氨气传感器受干扰气体影响较大不同的是,该传感器采用中红外分布反馈结构的带间级联激光器(distributed feedback inter-band cascade laser, DFB-ICL)为光源,工作波长在3 μm附近,避免了水和CO2干扰气体的影响,同时以空芯光波导（芯径1 mm、长度5 m）做气体池,采用自制多通道数字锁相放大器,同时解调1f和2f谐波信号,实现免校准测量,获得了传感器的梯度实验结果,线性度高达0.99917,不确定度高达0.9%。Allan方差评价结果显示其稳定性非常出色,在最佳积分时间167 s时,本传感器的检测限低至9.7 ppb。     

基于La0.7Sr0.3FeO3的微结构乙醇气体传感器的研制

以La0.7Sr0.3FeO3为敏感材料,设计制成了一种新型的共平面结构气体传感器.基于有限元分析软件Ansys对该传感器结构进行了优化设计.实验测得该传感器对于500ppm浓度乙醇气体的灵敏度为8.0,功耗为261mW,是同种敏感材料烧结型传感器功耗的2/3,响应时间约为1.5s,恢复时间约为2.5s,是一种功耗低、灵敏度高、稳定性好的微结构乙醇气体传感器.     

基于ZnO纳米结构的H2、NH3气体敏感性研究

通过简单的水热法在金电极上刺备了氧化锌纳米棒,从而制成了气体传感器。研究了氧化锌纳米棒的结构和特性,发现用该材料制成的气体传感器时于500ppm的NH3和H2在150℃下有较灵敏的反应,并探讨了产生传感效应的机理。该传感器制备方法简单、廉价、环保,适合大批量生产,有望应用于工业生产和日常生活的气体探测。     

Performance improvement in tensile-strained In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As metamorphic HEMT

This paper proposes a In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As (x=0.3-0.5-0.3) metamorphic high-electron mobility transistor with tensile-strained channel. The tensile-strained channel structure exhibits significant improvements in dc and RF characteristics, including extrinsic transconductance, current driving capability, thermal stability, unity-gain cutoff frequency, maximum oscillation frequency, output power, power gain, and power added efficiency.     

Very low-noise Al/sub 0.3/Ga/sub 0.7/As/Ga/sub 0.65/In/sub 0.35/As/GaAs single quantum-well pseudomorphic HEMTs

AlGaAs/GaInAs/GaAs pseudomorphic HEMTs with an InAs mole fraction as high as 35% in the channel has been successfully fabricated. The device exhibits a maximum extrinsic transconductance of 700 mS/mm. At 18 GHz, a minimum noise figure of 0.55 dB with 15.0 dB associated gain was measured. At 60 GHz, a minimum noise figure as low as 1.6 dB with 7.6 dB associated gain was also obtained. This is the best noise performance yet reported for GaAs-based HEMTs.<>     

A 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode array

We report a 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode (APD) array. The mean breakdown voltage of the APD was 57.9 V and the standard deviation was less than 0.1 V. The mean dark current was /spl sim/2 and /spl sim/300 nA, and the standard deviation was /spl sim/0.19 and /spl sim/60 nA at unity gain (V/sub bias/ = 13.5 V) and at 90% of the breakdown voltage, respectively. External quantum efficiency was above 40% in the wavelength range from 1.0 to 1.6 /spl mu/m. It was /spl sim/57% and /spl sim/45% at 1.3 and 1.55 /spl mu/m, respectively. A bandwidth of 13 GHz was achieved at low gain.     

Morphological and electrical characterization of SixCryCzBv thin films

Si_xCr_yC_zB_v thin films with several compositions have been studied for integration of high precision resistors in 0.8 μm BICMOS technology. These resistors, integrated in the back-end of line, have the advantage to provide high level of integration and attractive electrical behavior in temperature, for analog devices. The film morphology and the structure have been investigated through transmission electron microscopy analysis and have been then related to the electrical properties on the base of the percolation theory. According to this theory, and in agreement with experimental results, negative thermal coefficient of resistance (TCR) has been obtained for samples with low Cr content, corresponding to a crystalline volume fraction below the percolation threshold.Samples with higher Cr content exhibit, instead, a variation of the TCR as a function of film thickness: negative TCR values are obtained for thickness lower than 5 nm, corresponding to a crystalline volume fraction below the percolation threshold; positive TCR are obtained for larger thickness, indicating the establishment of a continuous conductive path between the Cr rich grains. This property seems to be determinant in order to assure the possibility to obtain thin film resistors almost independent on the temperature.     

Highly linear Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMTs

We report an Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMT with enhanced linearity. By engineering the channel region, i.e., inserting a 6-nm-thick AlGaN layer with 5% Al composition in the channel region, a composite-channel HEMT was demonstrated. Transconductance and cutoff frequencies of a 1 /spl times/100 /spl mu/m HEMT are kept near their peak values throughout the low- and high-current operating levels, a desirable feature for linear power amplifiers. The composite-channel HEMT exhibits a peak transconductance of 150 mS/mm, a peak current gain cutoff frequency (f/sub T/) of 12 GHz and a peak power gain cutoff frequency (f/sub max/) of 30 GHz. For devices grown on sapphire substrate, maximum power density of 3.38 W/mm, power-added efficiency of 45% are obtained at 2 GHz. The output third-order intercept point (OIP3) is 33.2 dBm from two-tone measurement at 2 GHz.     

Al/sub 0.3/Ga/sub 0.7/As/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) doped-channel field-effect transistors (DCFET's)

The properties of both lattice-matched and strained doped-channel field-effect transistors (DCFET's) have been investigated in AlGaAs/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) heterostructures with various indium mole fractions. Through electrical characterization of grown layers in conjunction with the dc and microwave device characteristics, we observed that the introduction of a 150-/spl Aring/ thick strained In/sub 0.15/Ga/sub 0.85/As channel can enhance device performance, compared to the lattice-matched one. However, a degradation of device performance was observed for larger indium mole fractions, up to x=0.25, which is associated with strain relaxation in this highly strained channel. DCFET's also preserved a more reliable performance after biased-stress testings.<>     

Comparison between Pt/TiO2/Pt and Pt/TaOX/TaOY/Pt based bipolar resistive switching devices

Nonvolatile memories have emerged in recent years and have become a leading candidate towards replacing dynamic and static random-access memory devices. In this article, the performances of TiO₂ and TaO₂ nonvolatile memristive devices were compared and the factors that make TaO₂ memristive devices better than TiO₂ memristive devices were studied. TaO₂ memristive devices have shown better endurance performances (10⁸ times more switching cycles) and faster switching speed (5 times) than TiO₂ memristive devices. Electroforming of TaO₂ memristive devices requires~4.5 times less energy than TiO₂ memristive devices of a similar size. The retention period of TaO₂ memristive devices is expected to exceed 10 years with sufficient experimental evidence. In addition to comparing device performances, this article also explains the differences in physical device structure, switching mechanism, and resistance switching performances of TiO₂ and TaO₂ memristive devices. This article summarizes the reasons that give TaO₂ memristive devices the advantage over TiO₂ memristive devices, in terms of electroformation, switching speed, and endurance.     

Broadband microwave noise characteristics of high-linearity composite-channel Al/sub 0.3/Ga/sub 0.7/N/Al/sub 0.05/Ga/sub 0.95/N/GaN HEMTs

We report broadband microwave noise characteristics of a high-linearity composite-channel HEMT (CC-HEMT). Owing to the novel composite-channel design, the CC-HEMT exhibits high gain and high linearity such as an output third-order intercept point (OIP3) of 33.2 dBm at 2 GHz. The CC-HEMT also exhibits excellent microwave noise performance. For 1-/spl mu/m gate-length devices, a minimum noise figure (NF/sub min/) of 0.7 dB and an associated gain (G/sub a/) of 19 dB were observed at 1 GHz, and an (NF/sub mi/) of 3.3 dB and a G/sub a/ of 10.8 dB were observed at 10 GHz. The dependence of the noise characteristics on the physical design parameters, such as the gate-source and gate-drain spacing, is also presented.