Novel capacitance-type humidity sensor based on multi-wall carbon nanotube/SiO2 composite films

A novel capacitance-type relative humidity (RH) sensor based on multi-wall carbon nanotubc/SiO2 (MWCNTs/SiO2) composite film is reported.Details of the fabrication process,possible sensing mechanism and sensing characteristics,such as linearity and sensitivity,are described.The capacitance of the MWCNTs/SiO2 composite film shows typical concentration percolation behavior with increasing MWCNT loading.At loadings below the percolation threshold (1.842wt％),the sensor capacitance increases obviously with increasing MWCNTs.The water condensed in the MWCNTs/SiO2 layer can lower the percolation threshold and increase the sensor capacitance.The sensor with MWCNT concentration of 1 wt％ has the best properties.The sensor has a humidity sensitivity of about 673 pF/％ RH and a linearity correlation of 0.98428.The response time of the sensor to RH is about 40 s and the recovery time is about 2 s.     

Resistive humidity sensor based on vanadium complex films

A resistive-type relative humidity （RH） sensor based on vanadium complex （VO2（3-f[）） film is reported in this study. Gold electrodes were deposited on the glass substrates in a co-planar structure. A thin film of vanadium complex was coated as a humidity-sensing material on the top of the pre-patterned electrodes. The humidity-sensing principle of the sensor was based on the conductivity change of coated sensing element upon adsorption/desorption of water vapor. The resistance of the humidity sensor measured at 1 kHz decreased linearly with increasing the humidity in the range of 35%-70% RH. The overall resistance of the sensor decreases 11 times. An equivalent circuit for the VO2（3-fl） based resistive-type humidity sensor was developed. The properties of the sensor studied in this work make it beneficial for use in the instruments for environmental monitoring of humidity.     

CO2 detection with CNx thin films deposited on porous silicon

In recent years, porous silicon (PSi) has attracted a great deal of attention for sensing applications. However, the high reactivity of PSi surfaces causes serious problems of stability. In this work, we developed new thin films that can serve as stabilizer of PSi for CO₂ gas sensors development. PSi surface was coated with carbon nitride (CN_x) film which is one of the most important interfering to stabilize the PSi layer. CN_x film was deposited by pulsed laser ablation. The effect of CO₂ gas on the sensor response was investigated for different polarization voltages. The electrical properties of (Al/CN_x/PSi/Si) structure were modified in the presence of the gas. The device shows a high sensitivity against CO₂ gas. Furthermore, the current variation of the sensor as a function of time has been investigated. The results show that the Al/CN_x/PSi/Si structure becomes stable after the first two weeks.     

CMOS工艺聚酰亚胺电容型湿度传感器的研究

以正胶光刻和干湿刻蚀方法,结合CMOS工艺制备了聚酰亚胺电容型湿度传感器.研究了硅基、钼-铝栅条状电极湿度传感器的结构及亚胺化温度对其性能的影响.结果表明:相对湿度(RH)为20%～80%发生准静态变化时,该传感器的湿度-电容曲线具有较好的线性度;外界相对湿度在12%和92%间发生阶跃变化时,响应时间约为40 s.     

Biological reaction signal enhancement in porous silicon Bragg mirror based on quantum dots fluorescence

In this paper, we mainly study the preparation of an optical biosensor based on porous silicon (PSi) Bragg mirror and its feasibility for biological detection. The quantum dot (QD) labeled biotin was pipetted onto streptavidin functionalized PSi Bragg mirror samples, the affinity reaction between QD labeled biotin and streptavidin in PSi occurred, so the QDs were indirectly connected to the PSi. The fluorescence of QD enhanced the signal of biological reactions in PSi. The performance of the sensor is verified by detecting the fluorescence of the QD in PSi. Due to the fluorescence intensity of the QDs can be enhanced by PSi Bragg mirror, the sensitivity of the PSi optical biosensor will be improved.     

多孔硅可见光发射研究

用常规电化学方法制备了发射高效可见光的多孔硅样品。对样品进行了光谱研究。用非化学方法从样品表面得到了粉末状荧光物质(非多孔硅膜研磨产物),光谱测定证实它的光致发光光谱与原多孔硅样品光致发光光谱相同,粉末进一步研磨后仍能发出同样的可见光。多孔硅样品还可以实现阴极射线激发发出同样的高效可见光,但易因电子束的轰击而发光强度较快减弱。用扫描电镜(SEM)对多孔硅样品的形貌、结构、荧光粉末的形状、尺寸、多孔硅样品阴极荧光发射区域进行了系统的研究。实验结果表明多孔硅样品一般可分为三层结构:表面层、多孔层和单晶硅衬底,样品荧光是来源于其表面层的。对样品表层组分的x射线光电子谱(XPS)分析表明,此时的多孔硅表层有大量非硅元素存在,如:C、O、F(没考虑H),硅元素的原子个数比只占30％～50％。用同样的电化学方法在单晶硅未抛光面上和多晶硅未抛光面上制得了均匀发射可见光样品。上述实验结果说明,多孔硅的高效可见光发射是来源于样品制备过程中在其表面层中形成的粉末状荧光物质。     

一种新型的CMOS集成湿度传感器

利用MEMS技术 ,对一种新型CMOS湿度传感器进行理论分析、模拟以及结果讨论。该湿度传感器采用标准CMOS工艺制造 ,采用梳状铝电极结构、梳状多晶硅加热结构 ,衬底接地 ,感湿介质采用聚酰亚胺 ,利用商业软件Coventor进行模拟绘制出敏感电容与相对湿度的曲线图。接口电路采用开关电容电路 ,输出可测电压信号 ,利用Microsim公司的Pspice模拟电路得到相对湿度与输出电压曲线关系     

复合钒钛酸干凝胶薄膜的湿敏特性研究

采用sol-gel法制备了复合钒钛酸干凝胶(H2V10Ti2O30-y·nH2O)薄膜,并对其湿敏特性进行了研究。结果表明:该薄膜为层状结构。用此薄膜制备的湿敏元件,在RH为11%～95%的范围内,感湿特性曲线线性好,其响应、恢复时间分别为5s和20s,湿滞为RH2%,感湿温度系数为RH0.45%/℃,并具有良好的稳定性。H2V10Ti2O30-y·nH2O干凝胶薄膜湿敏元件的灵敏度和湿滞均优于复合钒酸(H2V12O31-y·nH2O)干凝胶薄膜湿敏元件。     

Integration of a Chemical‐Responsive Hydrogel into a Porous Silicon Photonic Sensor for Visual Colorimetric Readout

The incorporation of a chemo‐responsive hydrogel into a 1D photonic porous silicon (PSi) transducer is demonstrated. A versatile hydrogel backbone is designed via the synthesis of an amine‐functionalized polyacrylamide copolymer where further amine‐specific biochemical reactions can enable control of cross‐links between copolymer chains based on complementary target–probe systems. As an initial demonstration, the incorporation of disulfide chemistry to control cross‐linking of this hydrogel system within a PSi Bragg mirror sensor is reported. Direct optical monitoring of a characteristic peak in the white light reflectivity spectrum of the incorporated PSi Bragg mirror facilitates real‐time detection of the hydrogel dissolution in response to the target analyte (reducing agent) over a timescale of minutes. The hybrid sensor response characteristics are shown to systematically depend on hydrogel cross‐linking density and applied target analyte concentration. Additionally, effects due to responsive hydrogel confinement in a porous template are shown to depend on pore size and architecture of the PSi transducer substrate. Sufficient copolymer and water is removed from the PSi transducer upon dissolution and drying of the hydrogel to induce color changes that can be detected by the unaided eye. This highlights the potential for future development for point‐of‐care diagnostic biosensing.     

SnO_2-LiZnVO_4系湿敏元件电容特性分析

采用共沉淀法制备SnO2-LiZnVO4系湿敏材料,研究了LiZnVO4的掺杂量对材料湿敏电容的影响。结果表明:LiZnVO4的掺杂量,环境的相对湿度(RH)、测试信号频率对湿敏电容有较大影响。当x(LiZnVO4)为10%时,可使材料具有合适的低湿电容和灵敏度。在100Hz下,当环境的RH从33%上升到93%时,SnO2-LiZnVO4系湿敏材料制备的湿敏元件的电容增量可达起始值的2300%,显示出较高的电容湿度敏感性。湿敏元件的电容响应时间约为54s,恢复时间约为60s。湿滞约为RH6%。     

基于倾斜光纤光栅的相对湿度传感器

提出了一种基于倾斜光纤光栅(TFBG)的包层上覆盖着聚乙烯醇(PVA)的空气相对湿度传感器,成功实现了对相对湿度在20～98%RH范围内的监测。研究发现,TFBG的透射功率在20～74%RH和74～98%RH2个相对湿度区域内分别呈现不同的线性变化,敏感度分别为2.52 dBm/%RH和14.95 dBm/%RH,并且在高湿度区有更高的敏感性。     

A label-free single photonic quantum well biosensor based on porous silicon for DNA detection

The single photonic quantum well (PQW) structures are successfully fabricated on p-type silicon wafer by electrochemical etching process, and are used for DNA detection firstly. The red shift of resonance peak is caused by the changing refractive index of PSi layer, which results from coupling of organic molecules into pores. When the porous silicon (PSi) based single PQW biosensors are immersed in complementary deoxyribonucleic acid (DNA) with different concentrations ranging from 0.625 μM to 10.000 μM, a good linear relationship is observed between the red shift of resonance peak and the complementary DNA concentration. Experimental results show that the detection sensitivity of PSi-based single PQW biosensors is 3.04 nm/μM with a detection limit of 32 nM for 16-base pair DNA oligonucleotides.     

Relative Humidity Sensor Based on Tilted Fiber Bragg Grating With Polyvinyl Alcohol Coating

A relative humidity (RH) sensor based on tilted fiber Bragg grating (TFBG) is proposed by utilizing polyvinyl alcohol (PVA) as the sensitive cladding film. RH increasing in the PVA coating will result in reduction of refractive index. Due to the TFBG's sensitivity to ambient refractive index, the spectral properties of PVA-coated TFBG are modified under exposure to different ambient humidity levels ranging from 20% to 98% RH. The transmission power of TFBG has different linear behaviors for two different humidity ranges (20%–74% RH and 74%–98% RH), and the sensitivity for each humidity range reaches as high as 2.52 and 14.947 dBm/%RH, respectively. Combining the advantages of optical fiber grating and PVA as a smart material, this design involves simple configuration, low cost, compactness, a small degree of hysteresis, stability, and wide dynamic sensing range as well. Therefore, the sensor could be applied in real-time RH monitoring for normal as well as extremely humid environments.      

Formation of two-layer composite-on-insulator structures based on porous silicon and SnO x . Study of their electrical and gas-sensing properties

The objective of this work is to fabricate and study multilayer “composite-on-insulator” sensor structures based on porous silicon and nonstoichiometric tin oxide. Two-layer structures “macroporous silicon-mesoporous silicon” on single-crystal silicon with sharp geometrical boundaries are grown. Test “composite-on-insulator” structures are fabricated. Oxide on macroporous silicon walls and a buried layer of oxidized mesoporous silicon play the role of the insulator. Nonstoichiometric tin oxide deposited onto the extended surface of oxidized macroporous silicon by chemical vapor deposition (CVD) is the sensitive layer. The gas sensitivity is studied upon exposure to NO₂ and degassing in air at room temperature. The sensitivity of the por-Si/SnO _x composite structures is higher than the sensitivity of tin-oxide film samples.     

Nano-photonic crystal formation on highly-doped n-type silicon

We present a novel electrochemical technique for the fabrication of nano-photonic crystal structures. Based on a specially designed electrolyte, porous silicon(PSi) layers with different porosities are possible to be produced on highly-doped n-type silicon substrate by varying the applied current density which determines the size and the morphology of pores. By applying an alternative current density modulation during anodization, porous silicon photonic crystals are obtained using HF-containing electrolyte without oxidizing components. The current burst model(CBM) is employed to interpret the mechanism of the formation of the macropore porous silicon.     

Experimental research of optical fiber hydrogen gas sensing system based on palladium-silver alloy

A novel optical fiber hydrogen sensing system based on palladium (Pd) and sliver (Ag) is proposed. By direct current (DC) magnetron process, Pd/Ag alloy ultra-thin films were deposited on the substrate to eliminate the hydrogen embrittlement of sensor based on pure Pd. Several samples with different thin film thicknesses were fabricated at different substrate temperatures and tested in the optical fiber hydrogen sensor setup. We do a series of experiments for obtaining optimum sputtering parameters, such as optimum sputtering temperature and thickness of Pd/Ag alloy film. The humidity effect and reliability experiment for the optical fiber hydrogen gas sensor are reported in detail. The testing results demonstrate the Pd/Ag alloy is a promising material for optical fiber hydrogen gas sensor.     

一种新型CMOS兼容湿度传感器

给出了与CMOS工艺兼容的一种新型梳齿状湿度传感器的结构、工艺流程及其测试结果.利用Coventor软件对这种新型结构进行了理论分析,对制备出的湿度传感器的性能如灵敏度、滞回特性、重复性、响应时间等进行了测试并讨论.结果表明文中提出的CMOS湿度传感器工艺简单、响应时间快、成本低、灵敏度高,有望在实际中得到应用.     

Effect of gamma irradiation on the photoluminescence of porous silicon

The effect of gamma irradiation on the luminescence properties of porous silicon produced by the electrochemical technique is studied. Changes in the photoluminescence intensity between irradiation doses and over a period of several days after the last irradiation are recorded. The quenching of photoluminescence at low irradiation doses and recovery after further irradiation are registered. It is found that porous silicon is strongly oxidized after gamma irradiation and the oxidation process continues for several days after irradiation. It is conceived that the change in the photoluminescence spectra and intensity of porous silicon after gamma irradiation is caused by a change in the passivation type of the porous surface: instead of hydrogen passivation, more stable oxygen passivation is observed. To stabilize the photoluminescence spectra of porous silicon, the use of fullerenes is proposed. No considerable changes in the photoluminescence spectra during irradiation and up to 18 days after irradiation are detected in a porous silicon sample with a thermally deposited fullerene layer. It is shown that porous silicon samples with a deposited C₆₀ layer are stable to gamma irradiation and oxidation.     

Specific features of the sol-gel formation and optical properties of 3d metal/porous silicon composites

The composition and optical properties of composite materials based on porous silicon with iron, cobalt, and nickel deposited by the sol-gel technique are studied. It is shown that the deposition of metal-oxide films onto the surface of porous silicon enables stabilization of the photoluminescence and an increase in its intensity, as well as the storage of hydrogen in the porous layer.     

共轭聚合物PFTQ/多孔硅复合膜的光致发光研究

为了实现硅基光电子集成,在多孔硅衬底上制备有机发光器件是一种很有优势的方法.采用匀胶机涂布法在多孔硅中嵌入了新型共轭有机聚合物聚(9,9-二辛基)-2,7-芴-co-N-(4-(2-苯基喹喔啉)苯)-4,4'-二苯胺(PFTQ),对比研究了多孔硅,PFTQ/多孔硅,PFTQ/硅以及PFTQ在甲苯溶液中的光致发光特性.实验结果表明:PFTQ/多孔硅复合膜光致发光强度是PFTQ/硅的2倍,而且相比在甲苯溶液中的PFTQ和PFTQ/硅,发光峰值有所红移,分析认为这是由于共轭聚合物在固态时有效共轭程度增加所致,并且与多孔硅中的激发载流子转移到聚合物分子上形成复合发光有关.