Sn-doped α-Fe2O3 patulous nanotubes for high performance formaldehyde sensing

SnO₂-doped α-Fe₂O₃ patulous microtubes (SFPNs) are synthesized by an electrospinning method. The as-synthesized materials are characterized by scanning electron microscope, X-ray powder diffraction and energy dispersive spectroscopy. The gas sensing results show SFPNs possess an excellent sensing property to formaldehyde. The response value of SFPNs gas sensor to 50 ppm formaldehyde is 25.4 at 220 ℃. The lowest detecting limit of 1 ppm formaldehyde is 3.2. Response and recovery characteristic curves of SFPNs gas sensors to 1, 2, 3, 5, 5, 3, 2 and 1 ppm formaldehyde are also tested. The results show a good reversibility and repeatability of SFPNs gas sensors. The sensor exhibits a high selectivity in the presence of acetone, ethanol, toluene, ammonia, hydrogen, carbon monoxide and butane. Moreover, the sensor has a good long-time stability.     

Toluene Sensing Properties of P4VP/Multi-Walle Carbon Nanotubes Multi-Layer Film Sensors

Poly4-vinylphenol (P4VP)/multi-wall carbon nanotubes(MWNTs) multi-layer sensitive films were deposited on interdigitated electrodes by airbrush technology to detect toluene vapor at room temperature.The surface and section morphologies of the multi-layer films were observed by a scanning electron microscope(SEM).It is found that the resistance of the sensor increases when it is exposed to toluene vapor and the response has a good linearity with the concentration of toluene.The results show that the P4VP/MWNTs three-layer film sensors have better sensing properties compared with the two-layer film sensors.The related sensing mechanism is studied in detail.     

Mesoporous tin oxide nanospheres for a NOx in air sensor

Mesoporous tin oxide(SnO₂/with a high surface area of 147.5 m²/g has been successfully synthesized via self-assembly process, combining the driven forces of water-evaporation and molecular interactions. Scanning electron microscope, X-ray diffraction, transmission electron micrograph, Fourier transform infrared and BrunauerEmmett-Teller were employed to analyze the morphology and crystal structure of the as-synthesized mesoporous materials. As a gas sensor, mesoporous SnO₂ shows impressive performances towards NOx gas with high selectivity and stability as well as ultra high sensitivity about 94.3 to 10 ppm NO_x gas at 300℃. The best response time of the sample S-500 is about 3.4s to 10 ppm NO_x at 450℃.     

In基复合半导体氧化物Cl2敏感特性的研究

Aiming at detecting Cl2 gas, this study was made on how to make In-based compound semiconductor oxide gas sensor. The micro-property and sensitivity of In-based gas sensing material were analyzed and its gas sensitive mechanism was also discussed. Adopting constant temperature chemical coprecipitation, the compound oxides such as In-Nb, In-Cd and In-Mg were synthesized, respectively. The products were sintered at 600 ℃ and characterized by the Scanning Electron Microscope （SEM）, showing the grain size almost about 50-60 nm. The test results show that the sensitivities of In-Nb, In-Cd and In-Mg materials under the concentration of 50 × 10^-6 in Cl2 gas are above 100 times, 4 times and 10 times, respectively. The response time of In-Nb, In-Cd and In-Mg materials is about 30, 60 and 30 s, and the recovery time less than 2, 10 and 2 min, respectively. Among them, the In-Nb material was found to have a relatively high conductivity and ideal sensitivity to Cl2 gas, which showed rather good selectivity and stability, and could detect the minimum concentration of 0.5 × 10^-6 with the sensitivity of 2.2, and the upper limit concentration of 500 × 10^-6. The power loss of the device is around 220 mW under the heating voltage of 3 V.     

Formaldehyde gas sensor based on TiO2 thin membrane integrated with nano silicon structure

An innovative formaldehyde gas sensor based on thin membrane type metal oxide of Ti O2 layer was designed and fabricated. This sensor under ultraviolet（UV） light emitting diode（LED） illumination exhibits a higher response to formaldehyde than that without UV illumination at low temperature. The sensitivities of the sensor under steady working condition were calculated for different gas concentrations. The sensitivity to formaldehyde of 7.14 mg/m³ is about 15.91 under UV illumination with response time of 580 s and recovery time of 500 s. The device was fabricated through micro-electro-mechanical system（MEMS） processing technology. First, plasma immersion ion implantation（PIII） was adopted to form black polysilicon, then a nanoscale TiO₂ membrane with thickness of 53 nm was deposited by DC reactive magnetron sputtering to obtain the sensing layer. By such fabrication approaches, the nanoscale polysilicon presents continuous rough surface with thickness of 50 nm, which could improve the porosity of the sensing membrane. The fabrication process can be mass-produced for the MEMS process compatibility.     

Excellent performance of gas sensor based on In2O3-Fe2O3 nanotubes

In₂O₃-Fe₂O₃ nanotubes are synthesized by an electrospinning method. The as-synthesized materials are characterized by scanning electron microscope and X-ray powder diffraction. The gas sensing results show that In₂O₃-Fe₂O₃ nanotubes exhibit excellent sensing properties to acetone and formaldehyde at different operating temperatures. The responses of gas sensors based on In₂O₃-Fe₂O₃ nanotubes to 100 ppm acetone and 100 ppm formaldehyde are 25 (240℃) and 15 (260℃), and the response/recovery times are 3/7 s and 4/7 s, respectively. The responses of In₂O₃-Fe₂O₃ nanotubes to 1 ppm acetone (240℃) and formaldehyde (260℃) are 3.5 and 1.8, respectively. Moreover, the gas sensor based on In₂O₃-Fe₂O₃ nanotubes also possesses an excellent selectivity to acetone and formaldehyde.     

Nano-WO3 film modified macro-porous silicon（MPS） gas sensor

We prepared macro-porous silicon（MPS） by electrochemical corrosion in a double-tank cell on the surface of single-crystalline P-type silicon.Then,nano-WO₃ films were deposited on MPS layers by DC facing target reactive magnetron sputtering.The morphologies of the MPS and WO₃/MPS samples were investigated by using a field emission scanning electron microscope.The crystallization of WO₃ and the valence of the W in the WO₃/MPS sample were characterized by X-ray diffraction and X-ray photoelectron spectroscopy,respectively. The gas sensing properties of MPS and WO₃/MPS gas sensors were thoroughly measured at room temperature. It can be concluded that:the WO₃/MPS gas sensor shows the gas sensing properties of a P-type semiconductor gas sensor.The WO₃/MPS gas sensor exhibits good recovery characteristics and repeatability to 1 ppm NO₂.The addition of WO₃ can enhance the sensitivity of MPS to NO₂.The long-term stability of a WO₃/MPS gas sensor is better than that of an MPS gas sensor.The sensitivity of the WO₃/MPS gas sensor to NO₂ is higher than that to NH₃ and C₂H₅OH.The selectivity of the MPS to NO₂ is modified by deposited nano-WO₃ film.     

MOCVD方法在蓝宝石衬底上生长无应变InAlN/GaN异质结材料研究

In Al N/Ga N heterostructures were grown on sapphire substrates by low-pressure metal organic chemical vapor deposition.The influences of NH3 flux and growth temperature on the In composition and morphologies of the In Al N were investigated by X-ray diffraction and atomic force microscopy.It’s found that the In composition increases quickly with NH3 flux decrease.But it’s not sensitive to NH3 flux under higher flux.This suggests that lower NH3 flux induces a higher growth rate and an enhanced In incorporation.The In composition also increases with the growth temperatures decreasing,and the defects of the In Al N have close relation with In composition.Unstrained In Al N with In composition of 17% is obtained at NH3 flux of 500 sccm and growth temperature of790 °C.The In Al N/Ga N heterostructure high electron mobility transistor sample showed a high two-dimensional electron gas(2DEG) mobility of 1210 cm2/(V s) with the sheet density of 2.31013cm2 at room temperature.     

终端式MEMS微波功率传感器的设计与制作

A terminating type MEMS microwave power sensor based on the Seebeck effect and compatible with the GaAs MMIC process is presented. An electrothermal model is introduced to simulate the heat transfer behavior and temperature distribution. The sensor measured the microwave power from –20 to 20 dBm up to 20 GHz. The sensitivity of the sensor is 0.27 mV/mW at 20 GHz, and the input return loss is less than –26 dB over the entire experiment frequency range. In order to improve the sensitivity, four different types of coplanar waveguide （CPW） were designed and the sensitivity was significantly increased by about a factor of 2.     

Piezoresistive Sensors Based on Carbon Nanotube Films

Piezoresistive effect of carbon nanotube films was investigated by a three-point bending test. Carbon nanotubes were synthesized by hot filament chemical vapor deposition. The experimental results showed that the carbon nanotubes have a striking piezoresistive effect. The relative resistance was changed from 0 to 10.5 X 10-2 and 3.25 X 10-2 for doped and undoped films respectively at room temperature when the microstrain under stress from 0 to 500. The gauge factors for doped and undoped carbon nanotube films under 500 microstrain were about 220 and 67 at room temperature, respectively, exceeding that of polycrystalline silicon (30) at 35 ℃. The origin of the resistance changes in the films may be attributed to a strain-induced change in the band gap for the doped tubes and the defects for the undoped tubes.     

高效太阳电池硅衬底特性对原子层沉积Al2O3薄膜钝化性能的影响

Atom layer deposition （ALD）-Al2O3 thin films are considered effective passivation layers for p-type silicon surfaces. A lower surface recombination rate was obtained through optimizing the deposition parameters. The effects of some of the basic substrate characteristics including material type, bulk resistivity and surface morphology on the passivation performance of ALD-Al2O3 are evaluated in this paper. Surface recombination velocities of 7.8 cm/s and 6.5 cm/s were obtained for p-type and n-type wafers without emitters, respectively. Substrates with bulk resistivity ranging from 1.5 to 4 Ω · cm were all great for such passivation films, and a higher implied Voc of 660 mV on the 3 Ω · cm substrate was achieved. A minority carrier lifetime （MCL） of nearly 10 μs higher was obtained for cells with a polished back surface compared to those with a textured surface, which indicates the necessity of the polishing process for high-efficiency solar cells. For n-type semi-finished solar cells, a lower effective front surface recombination velocity of 31.8 cm/s was acquired, implying the great potential of （ALD）-Al2O3 thin films for high-efficiency n-type solar cells.     

超薄SiO2/HfO2双层栅介质的时变击穿特性和击穿机制的研究

The characteristics of TDDB （time-dependent dielectric breakdown） and SILC （stress-induced leakage current） for an ultra-thin SiO2/HfO2 gate dielectric stack are studied. The EOT （equivalent-oxide-thickness） of the gate stack （Si/SiO2/HfOz/TiN/TiA1/TiN/W） is 0.91 am. The field acceleration factor extracted in TDDB experi- ments is 1.59 s.cm/MV, and the maximum voltage is 1.06 V when the devices operate at 125 ℃ for ten years. A detailed study on the defect generation mechanism induced by SILC is presented to deeply understand the break- down behavior. The trap energy levels can be calculated by the SILC peaks： one S1LC peak is most likely to be caused by the neutral oxygen vacancy in the HfO2 bulk layer at 0.51 eV below the Si conduction band minimum; another SILC peak is induced by the interface traps, which are aligned with the silicon conduction band edge. Fur- thermore, the great difference between the two SILC peaks demonstrates that the degeneration of the high-k layer dominates the breakdown behavior of the extremely thin gate dielectric.     

Synthesis of In2S3 thin films by spray pyrolysis from precursors with different [S]/[In] ratios

Indium sulfide （InzS3） thin films were prepared by chemical spray pyrolysis technique from solutions with different [S]/[In] ratios on glass substrates at a constant temperature of 250 ~C. Thin films were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, atomic force microscopy （AFM）, energy disper- sive X-ray spectroscopy （EDS）, Raman spectroscopy and optical transmittance spectroscopy. All samples exhibit a polycrystalline structure with a preferential orientation along （0, 0, 12）. A good stoichiometry was attained for all samples. The morphology of thin film surfaces, as seen by SEM, was dense and no cracks or pinholes were ob- served. Raman spectroscopy analysis shows active modes belonging to j3-1naS3 phase. The optical transmittance in the visible range is higher than 60% and the band gap energy slightly increases with the sulfur to indium ratio, attaining a value of 2.63 eV for [S]/[In] ： 4.5.     

Ga2O3缓冲层厚度对柔性衬底沉积Cu/ITO薄膜性能的影响

Cu and Cu/ITO films were prepared on polyethylene terephthalate （PET） substrates with a Ga2O3 buffer layer using radio frequency （RF） and direct current （DC） magnetron sputtering. The effect of Cu layer thickness on the optical and electrical properties of the Cu film deposited on a PET substrate with a Ga2O3 buffer layer was studied, and an appropriate Cu layer thickness of 4.2 nm was obtained. Changes in the optoelectrical properties of Cu（4.2 nm）/ITO（30 nm） films were investigated with respect to the Ga2O3 buffer layer thickness. The optical and electrical properties of the Cu/ITO films were significantly influenced by the thickness of the Ga2O3 buffer layer. A maximum transmission of 86%, sheet resistance of 45 Ω/□ and figure of merit of 3.96 × 10^-3 Ω^ -1 were achieved for Cu（4.2 nm）/ITO（30 nm） films with a Ga2O3 layer thickness of 15 nm.     

TiO2 薄膜CMP表面粗糙度的研究

Abstract： Surface roughness by peaks and depressions on the surface of titanium dioxide （TiO2） thin film, which was widely used for an antireflection coating of optical systems, caused the extinction coefficient increase and affected the properties of optical system. Chemical mechanical polishing （CMP） is a very important method for surface smoothing. In this polishing experiment, we used self-formulated weakly alkaline slurry. Other process parameters were working pressure, slurry flow rate, head speed, and platen speed. In order to get the best surface roughness （1.16 A, the scanned area was 10 × 10 μm2） and a higher polishing rate （60.8 nm/min）, the optimal parameters were： pressure, 1 psi; slurry flow rate, 250 mL/min; polishing head speed, 80 rpm; platen speed, 87 rpm.     

不同氧化退火工艺下SiO2/SiC界面特性研究

The effect of the different re-oxidation annealing （ROA） processes on the SiO2/SiC interface charac- teristics has been investigated. With different annealing processes, the flat band voltage, effective dielectric charge density and interface trap density are obtained from the capacitance-voltage curves. It is found that the lowest interface trap density is obtained by the wet-oxidation annealing process at 1050 ℃ for 30 min, while a large num- ber of effective dielectric charges are generated. The components at the SiO2/SiC interface are analyzed by X-ray photoelectron spectroscopy （XPS） testing. It is found that the effective dielectric charges are generated due to the existence of the C and H atoms in the wet-oxidation annealing process.     

一种应用于无线局域网具有3.01-3.82 GHz频率范围和6.29%调谐增益变化的CMOS LC压控振荡器

A wideband low-phase-noise LC voltage-controlled oscillator （VCO） with low VCO gain （Kvco） vari- ation for WLAN fractional-N frequency synthesizer application is proposed and designed on a 0.13-μm CMOS process. In order to achieve a low Kvco variation, an extra switched varactor array was added to the LC tank with the conventional switched capacitor array. Based on the proposed switched varactor array compensation technique, the measured Kvco is 43 MHz/V with only 6.29% variation across the entire tuning range. The proposed VCO provides a tuning range of 23.7% from 3.01 to 3.82 GHz, while consuming 9 mA of quiescent current from a 2.3 V supply. The VCO shows a low phase noise of-121.94 dBc/Hz at 1 MHz offset, from the 3.6 GHz carrier.     

采用Ni/Ti/Ni多层金属在N型4H-SiC衬底改善粘附性和界面的欧姆接触

The Ni/Ti/Ni multilayer ohmic contact properties on a 4H-SiC substrate and improved adhesion with the Ti/Au overlayer have been investigated. The best specific contact resistivity of 3.16 × 10^-5 Ω.cm^2 was obtained at 1050 ℃. Compared with Ni/SiC ohmic contact, the adhesion between Ni/Ti/Ni/SiC and the Ti/Au overlayer was greatly improved and the physical mechanism under this behavior was analyzed by using Raman spectroscopy and X-ray energy dispersive spectroscopy （EDS） measurement. It is shown that a Ti-carbide and Ni-silicide compound exist at the surface and there is no graphitic carbon at the surface of the Ni/Ti/Ni structure by Raman spectroscopy, while a large amount of graphitic carbon appears at the surface of the Ni/SiC structure, which results in its bad adhesion. Moreover, the interface of the Ni/Ti/Ni/SiC is improved compared to the interface of Ni/SiC.     

一款采用跨导增强技术的新型宽带低噪声放大器

A new broadband low-noise amplifier （LNA） is proposed. The conventional common gate （CG） LNA exhibits a relatively high noise figure, so active gin-boosting technology is utilized to restrain the noise generated by the input transistors and reduce the noise figure. Theory, simulation and measurement are shown. An implemented prototype using 0.13 μm CMOS technology is evaluated using on-wafer probing. S11 and S22 are below -10 dB across 0.1-5 GHz. Measurements also show a gain of 18.3 dB with a 3 dB bandwidth from 100 MHz to 2.1 GHz and an ⅡP3 of-7 dBm at 2 GHz. The measured noise figure is better than 2.5 dB below 2.1 GHz, is better than 4.5 dB below 5 GHz, and at 500 MHz, it gets its minimum value 1.8 dB. The LNA consumes 9 mA from 1.5 V supply and occupies an area of 0.04 mm^2.     

The total dose effects on the 1/f noise of deep submicron CMOS transistors

Using 0.18 μm CMOS transistors, the total dose effects on the 1/f noise of deep-submicron CMOS transistors are studied for the first time in mainland China. From the experimental results and the theoretic analysis, we realize that total dose radiation causes a lot of trapped positive charges in STI （shallow trench isolation） SiO2 layers, which induces a current leakage passage, increasing the 1/f noise power of CMOS transistors. In addition, we design some radiation-hardness structures on the CMOS transistors and the experimental results show that, until the total dose achieves 750 krad, the 1/f noise power of the radiation-hardness CMOS transistors remains unchanged, which proves our conclusion.