高空湿度探测用加热式湿度传感器的研制

为实现高空高湿环境下对湿度的准确测量,本文设计和研究了集成加热功能的湿度传感器,在探空仪进行高空湿度探过程中利用两只加热式湿度传感器进行轮流加热除湿和湿度测量。通过对聚酰亚胺湿敏材料进行改性和合成,设计和制作了加热式的电容型湿度传感器,其灵敏度为0.2195 pF/%RH、响应时间小于1 s、湿滞为4.8%RH、半年漂移量在±0.3%RH以内。通过分析不同温度下的加热恢复时间,制定了加热式湿度传感器轮流工作的机制,轮流加热时间和周期分别为2s和120 s。并利用数据采集电路以及GPS探空仪对加热式湿度传感器进行了地面静态性能和高空动态性能测试,其高空湿度探测结果与VA SALA RS92的显示出较好的一致性和较低的湿度误差。本文研制的加热式湿度传感器能具有良好的地面性能,实现了交替加热除湿和湿度测量的功能,具有高空湿度探测的应用潜力。     

Nano-grass polyimide-based humidity sensors

This paper deals with a micro-capacitive-type relative humidity sensor with nano-grass polyimide as a dielectric sensing material. Our humidity sensor achieves key performance indices such as quick response, high sensitivity, and stability enabled by the modification of polyimide into nano-grass morphology where the dimension of a typical individual pillar is 387 nm × 40 nm. A low hysteresis operation is also achieved by integrating a micro-heater in the sensing area. The nano-grass morphology is created with an oxygen plasma treatment on polyimide surface which increases surface to volume ratio by more than 280 times larger than that of a simple flat-film. This amplification of the surface to volume ratio leads to the rapid adsorption and desorption of water into the sensing material. Furthermore the oxygen plasma treatment introduces a carbonyl group that facilitates an enhanced affinity of the polyimide surface to water molecules. XPS analysis is used to confirm the emergence of carbonyl groups as a result of the treatment. The total response time of a nano-grass sensor is 11 s which is improved by about 2.5 times than a normal flat-film sensor. The sensitivity of the nano-grass sensor is 0.08 pF/%RH (relative humidity) which is improved by 8 times compared with the flat-film one. In stability test for 200 h, the signal of the nano-grass sensor is fluctuated ±1.0%RH. Theoretical models employing the Looyenga and Dubinin equations are used to explain the behavior of the nano-grass sensor.     

MEMS-based humidity sensor with integrated temperature compensation mechanism

This study applies conventional micro-electro-mechanical systems (MEMS) techniques to develop a novel low-cost humidity sensor comprising a silicon substrate, a freestanding cantilever and an integrated resistive thermal sensor. The cantilever has a composite structure comprising a thin layer of platinum (Pt) deposited on a silicon nitride layer and then covered with a polyimide sensing layer. The cantilever deflected in the upward direction as water molecules absorbed by the polyimide sensing layer. The humidity sensor chip caused a measurable change in the resistance of the platinum layer. By compensating the change in the measured resistance by the ambient temperature, the absolute value of the relative humidity can be directly derived. The experimental results show that the sensor has a time-response of 0.9 s when exposed to a sudden humidity change of 65%RH to 95%RH. The sensitivity of the sensors decreases as the temperature increases. Furthermore, the sensor with the longest Pt resistor has the greatest sensitivity. In additions, the temperature-calibrated resistance signal generated by the sensor varies linearly with the ambient humidity.     

Fast response resistive humidity sensitivity of polyimide/multiwall carbon nanotube composite films

In this study, the fast response resistive humidity sensing properties of polyimide/multiwall carbon nanotube (PI/MWNT) composite films were demonstrated. A composite film with a loading of 3 wt% MWNTs possesses a very linear response nature, a linearity correlation (R²) of 0.99157 and a sensitivity of 0.00146/%RH. The response time was less than 5 s and the resistance changed synchronously with different humidities. The recoverable and repeatable resistive responses affirmed the high efficiency of this film for fast humidity detection. A negative temperature effect was found and proper temperature compensation should be considered in the future applications. Moreover, the humidity sensing properties were presented as a bulk effect owing to water penetration. The stability of the films was proven, which further confirmed that the films could be used as reliable sensor materials. The surfaces of the films were found as an organized structure with nano-size dimples, which is helpful for absorption of water molecules. The proposed sensing mechanisms are related with tunnel effects, doping of MWNTs by water and a barrier effect between MWNTs.     

基于MEMS工艺的压阻式湿度传感器的设计制作

提出用硅-硅直接键合的SOI片制作压阻式湿度传感器.它是利用涂覆在硅膜上聚酰亚胺膜吸湿发生膨胀,导致双膜结构发生弯曲产生应力的原理进行工作的.为了确定传感器结构、优化尺寸,采用ANSYS软件进行了模拟计算、设计了MEMS湿度传感器的制造工艺,对制作的微湿度传感器进行了测试,其灵敏度为0.21 mV%RH,最大湿滞为8%RH.     

基于LCP衬底的柔性湿度传感器研究

介绍了一种新型柔性电容式湿度传感器.该柔性电容式湿度传感器采用液晶高分子聚合物(LCP)作为衬底,金属铜(Cu)作为叉指电极,聚酰亚胺(PI)作为湿度传感器的湿敏介质.LCP衬底的应用使得该传感器具有良好的柔性和可弯曲性.该柔性湿度传感器与传统硅基湿度传感器相比较具有成本低廉、结构简单、制作方便等优点.该柔性湿度传感器在25℃下的平均灵敏度为0.04%pF/%RH,最大回滞为±4.16%RH,其平均灵敏度在25℃~70℃范围内受温度影响较小.在25℃下其响应时间和恢复时间分别为36 s和39 s.该柔性湿度传感器可以应用于环境湿度检测、人工电子皮肤系统和可穿戴设备等领域.     

High relative humidity measurements using gelatin coated long-period grating sensors

A long-period grating (LPG) coated with gelatin was developed as a high relative humidity (RH) sensor. The resonance dip or coupling strength of the LPG spectrum varies with RH. Experimental investigations on the sensor yield a sensitivity of 0.833%RH/dB with an accuracy of ±0.25%RH, and a resolution of ±0.00833%RH. The LPG RH sensor also offers repeatability, hysteresis and stability errors of less than ±0.877, ±0.203 and ±0.04%RH, respectively. In addition to the characterization of the LPG RH sensor, further studies were conducted to determine the effect of grating periodicities on the sensitivity of the sensor. Results show that higher order cladding modes from smaller grating periods enable the sensor to achieve higher sensitivity to humidity. This method is proposed to be more cost effective as compared to more complex spectroscopic methods based on wavelength detection. This sensor can also help to solve problems in measuring high humidity with existing relative humidity measurement systems.     

A high-sensitivity polyimide capacitive relative humidity sensorfor monitoring anodically bonded hermetic micropackages

This paper presents the design, fabrication and complete characterization of a high-sensitivity polyimide-based humidity sensor for monitoring internal humidity level in anodically bonded hermetic micropackages. This capacitive sensor is 1 mm on a side and utilizes CU1512 polyimide film with a thickness in the range from 300 Å to 1200 Å sandwiched between two metal electrodes to sense moisture. The measured sensitivity for a sensor with a 1200-Å-thick film is 0.86 pF/%RH, and for a 300-Å-thick sensor is 3.4 pF/%RH. The sensor has been exposed to and survived a one-hour test at 400°C, which is the temperature typically used to perform anodic bonding. Measurements show a drift of less than 1% RH at 50% RH and 37°C for 48 h, and a hysteresis of <2% RH over a range from 30 to 70% RH for a 1200-Å-thick polyimide film sensor. The measured breakdown voltage of the sensor (1200 Å thick) exceeds 20 V and agrees well with other results     

基于MWCNTs/Nafion复合膜的高性能声表面波湿敏传感器研究

湿度检测广泛应用于工业、医疗等各个领域,对高性能湿度传感器的需求日趋迫切。首先对声表面波传感器敏感机理进行了深入的分析,得到影响其性能的主要因素。在此基础上研制出一种以多壁碳纳米管(MWCNTs)和Nafion复合材料为湿敏膜,高频声表面波谐振器为换能元件的高性能湿敏传感器。实验表明,制得的湿敏传感器在宽湿度范围内(1...     

Capacitive humidity sensors based on a newly designed interdigitated electrode structure

This paper presents a study of capacitive humidity sensors constructed based on a newly designed interdigitated electrode (IDE) structure with a polyimide (PI) sensing layer fabricated using micro-electro-mechanical system (MEMS) technology. The humidity sensors use an IDE with increased height, formed by the surface micromachining of a silicon substrate. The fabricated sensors showed higher sensitivity in variable ambient relative humidity (RH) when compared with the humidity sensors of a conventional IDE since the horizontal electric field lines, generated between the thick electrodes, are confined to the PI sensing layer. The effect of the thickness of the PI layer was also investigated. The fabricated sensors with a 4-μm-thick PI layer showed a higher sensitivity of 37.1 fF/%RH when compared with those of a 2- and 3-μm-thick PI layers, indicating that the properties of the sensors depend on the thickness of the PI layer. This is because the amount of the fringing electric field lines passing through the PI is determined by the PI thickness. In addition, the sensor with the 4-μm-thick PI showed very slight hysteresis with a maximum of 2.87%RH and displayed high stability with a variation range of 0.06 pF.     

基于金属有机框架化合物修饰的QCM湿度传感器

提出一种基于自行合成的钴金属框架化合物Co2(oda)2(4,4’-bipy)修饰的石英晶体微天平(QCM)的新型湿度传感器,研究了其制备条件、不同溶剂和不同修饰量对传感器性能的影响。实验结果表明:水在1.2×10-6～20×10-6范围内与频率变化量呈良好的线性关系,其相关系数为0.99903,检测灵敏度可达到87.40 Hz/10-6,检测限为0.16×10-6(信噪比为3∶1)。将此传感器在实际环境中对11%～95%RH进行了检测,结果显示频率对数变化logΔf与%RH呈良好的线性关系,其线性方程为logΔf=1.414 2+0.018 18%RH,R=0.999 65。该湿度传感器具有制备简单、体积小、选择性好、灵敏度高、稳定性好等特点,为湿度检测提供了一个新的方法。     

片上加热电容式湿度传感器研究

提出了一种集成加热结构的电容式湿度传感器结构。对传感器的稳态加热特性进行了分析,并利用红外线热成像技术对传感器加热过程以及稳态温度响应进行了研究。在5 V电压信号的加热下,传感器温度上升约30℃,且温度分布均匀,传感器敏感区域温差<4℃。在加热与不加热条件下,分别对传感器的湿度敏感特性与响应时间特性进行了测试。不加热时,传感器的灵敏度为0.00913 pF/%rH,回滞≈0.12 pF,响应时间约120.8 s;以5 V脉冲信号加热后,传感器灵敏度为0.00903 pF/%rH,最大回滞≈0.025 pF,响应时间约75.2 s。加热后传感器性能有了显著提高。     

Optical humidity sensor using porphyrin immobilized Nafion composite films

A Nafion–TMPyP composite film was used in an optical humidity sensor. The composites were prepared with various molar ratios between the sulfonic groups and TMPyP molecules, R = [–SO₃H]/[TMPyP]. The UV–vis measurement of the composite films suggested that the TMPyP molecules were well dispersed at in the range of R = 60–100, but formed aggregates at R ≤ 20. Furthermore, the FTIR indicated that sulfonic group interacted with TMPyP. The reflectance change with relative humidity (%RH) occurred at 426.4 and 465.4 nm with the isosbestic point at 437.5 nm, and also in the Q-band region. The sensors of R = 30 and 40 sensitively responded to humidity in the lower humidity region (10–20%RH), but saturated or even decreased with further increase in humidity. At R = 60, the sensitivity slightly decreased but a measurable range was extended to around 70%RH. Remarkable deterioration in sensitivity occurred at R = 100. The TMPyP molecules were stably immobilized on a Nafion matrix, even in liquid water, without solving out.     

Measurement of the thermal conductivity anisotropy in polyimidefilms

Polymer films are playing an important role in the development of micromachined sensors and actuators, fast logic circuits, and organic optoelectronic devices. The thermal properties of polyimide films govern the temporal response of many micromachined thermomechanical actuators, such as ciliary arrays. This work develops three experimental techniques for measuring both the in-plane and the out-of-plane thermal conductivities of spin-coated polyimide films with thicknesses between 0.5 and 2.5 μm, which are common in MEMS. Two of the techniques use transient electrical heating and thermometry in micromachined structures to isolate the in-plane and out-of-plane components. These techniques establish confidence in a third, simpler technique, which measures both components independently and uses IC-compatible processing. The data illustrate the anisotropy in the thermal conductivity of the polyimide films investigated here, with the in-plane conductivity larger by a factor between four and eight depending on film thickness and temperature. The anisotropy diminishes the time constants of thermal actuators made from polyimide films     

Thick films of copper-titanate resistive humidity sensor

The humidity-sensitive TiO₂-Cu₂O-Na₂O thick films were prepared by screen printing on alumina substrates and subsequent firing. Pastes for screen printing were obtained by adding an organic vehicle and binder to TiO₂-Cu₂O-Na₂CO₃ powders. The microstructure of the films changed with the content of the sodium oxide and the firing temperatures. When the resistance characteristics of the sensors obtained from TiO₂-Cu₂O-Na₂O, 10-2-1 were measured, the resistance changed linearly in its semi-logarithmic graph. The resistance varied from 10⁷ to 10⁴ Ω between 20 and 95%RH, which was required for a common humidity sensor. Temperature dependence, frequency dependence and response time were also measured and estimated.     

WO_3/Si-NPA复合薄膜的电容湿度传感性能研究

制备了基于硅纳米孔柱阵列(Si-NPA)的WO3/Si-NPA复合薄膜,并对其表面形貌进行了表征,研究了其电容湿度传感性能和基点电容的温度漂移。研究表明:WO3/Si-NPA继承了衬底Si-NPA规则的阵列结构的表面形貌特征,WO3的沉积形成了连续的WO3薄膜,WO3/Si-NPA是一种典型的纳米复合薄膜。室温下,WO3/Si-NPA的电容值随测试频率的增加而单调减小,但其灵敏度则在100 Hz时达到最大值。在此测试频率下,当环境的相对湿度从11%RH增加到95%RH时,元件的电容增量高达16 000%,显示WO3/Si-NPA对环境湿度有较高的灵敏度。同时,电容的湿度响应曲线显示出很好的线性。对其基点电容的温度稳定性研究表明:WO3/Si-NPA用作湿度传感的最佳工作温度区为15~50℃。     

一种电压输出型CMOS集成电容湿度传感器

设计一种湿度传感器。该传感器选用聚酰亚胺作为湿度传感器的感湿介质,采用叉指电容式结构以增加感湿灵敏度,以电荷转移电路为微电容测量电路,用0.35μm多晶硅栅进行设计,形成单片集成湿度传感器。整个组成电路均与CMOS工艺兼容。仿真结果表明:在测量激励方波激励下,片上湿度传感器在27℃下模拟显示出较好的直流电压输出特性。     

Fabrication of micro sensors on a flexible substrate

Flexible micro temperature and humidity sensors on parylene thin films were designed and fabricated using a micro-electro-mechanical-systems (MEMS) process. Based on the principles of the thermistor and the ability of a polymer to absorb moisture, the sensing device comprised gold wire and polyimide film. The flexible micro sensors were patterned between two pieces of parylene thin film that had been etched using O₂ plasma to open the contact pads. The sacrificial Cr spacer layer was removed from the Cr etchant to release the flexible temperature and humidity sensors from the silicon substrate. Au was used to form the sensing electrode of the sensors while Ti formed the adhesion layer between the parylene and Au. The thickness of the device was 7 ± 1 μm, so the sensors attached easily to highly curved surfaces. The sensitivities of the temperature and humidity sensor were 4.81 × 10⁻³ °C⁻¹ and 0.03 pF/%RH, respectively. This work demonstrates the feasibility and compatibility of thin film sensor applications based on flexible parylene. The sensor can be applied to fuel cells or components that must be compressed.     

多孔硅相对湿度传感器的设计

基于对三明治型与平铺型两种多孔硅湿度传感器结构的灵敏度分析与比较,结合两种结构的优点,设计出新的传感器的结构。通过对该结构湿度传感器的性能测试,得出该传感器的灵敏度为1.1 pF/RH%,响应时间为73 s,温度湿度系数为0.5%RH/℃,该湿度传感器适用于在中低湿环境中测量,在每隔20 d的时间对传感器跟踪测试,证明该传感具有较好的稳定性。此外为了传感器可以自解吸附,该传感器采用多晶硅为传感器加热除湿,在金属电极上溅射一层钝化层以防止电极被水汽腐蚀。     

Thin polymer film based rapid surface acoustic wave humidity sensors

Polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) thin films, deposited on the surface of glass slides, were studied using transmission FTIR spectroscopy upon varying relative humidity (RH) from 2 to 70%. The obtained data revealed fast dynamics of water vapor adsorption-desorption with responses on the order of several seconds. Based on the fast FTIR signal intensity changes versus RH, it was proposed that a similar rapid response can be achieved for PVA and PVP coated SAW devices due to changes in mass-loading and film viscoelastic properties upon absorption of water vapor in the films. Sub-micron thickness films were spin-coated onto the surface of LiNbO₃ SAW substrates. Both PVA and PVP based humidity sensors revealed prompt reversible response to variations in humidity, although PVP-based device demonstrated better sensor parameters with total insertion loss variation of about 50 dB over the studied RH range and response time 1.5 s for the humidity step 5-95% (recovery time - 2.5 s), representing one of the fastest SAW-based humidity sensors reported to date.