A High-Aspect-Ratio Process with Nylon Membrane Filters for Fabricating Miniaturized Devices
Date Issued
2016
Date
2016
Author(s)
Ma, Cheng-Wen
Abstract
This work proposed a novel lithography process for fabricating a patterned SU-8 mold on a nylon membrane filter. The proposed technique is employed to realize various miniaturized devices, including a flexible tactile and shear sensing array, a supercapacitor, and a highly sensitive tactile sensing array. A flexible tactile and shear sensing array incorporating patterned buckypaper as the sensing elements and presents a novel process for patterning buckypaper at a high aspect ratio. The fabricated sensing device features advantages such as an anisotropic sensing capability, flexibility, ease of fabrication, and a low cost. Analyzing the measured resistance versus applied shear force on a single sensing element revealed that the sensitivity of the element varied along different directions. This anisotropic sensing capability can be employed to improve shear sensing. In addition, the sensing elements exhibited favorable sensitivity and repeatability. Force images were obtained using a 2 × 2 shear-force sensing array when various normal and shear forces were applied. We further proposed a paper-like micro-supercapacitor with in-plane interdigital buckypaper electrodes on a filter membrane substrate in this thesis. A vacuum filtration method assisted by lithography techniques was proposed for patterning the buckypaper. The benefits of the proposed micro-SC include a flexible structure, simple fabrication, easy chip integration, and high specific capacitance. By increasing the aspect ratio of the patterned buckypaper electrodes, the specific capacitance of the micro-SC was effectively enhanced. The specific capacitance measured using cyclic voltammetry was 107.27 mF/cm2 at a scan rate of 20 mV/s. The measured charge–discharge behaviors at various discharge rates revealed the electrochemical stability of the device. The measured leakage current was approximately 9.95 µA after 3600 s. The device exhibited high cycle stability with 96.59% specific capacitance retention after 1000 cycles. Also, we proposed a highly sensitive tactile sensing array. Sensing elements of the array comprise multiwall carbon nanotubes and polydimethylsiloxane polymer. A novel lithography process is proposed for fabricating an SU-8 mold for shaping the sensing cells in the array. In addition, a nylon membrane filter is proposed to serve as a mold for numerous microdome patterns, which were transferred onto a conductive polymer film. The proposed device features advantages, such as ultra-high sensitivity, flexibility, and a simple fabrication process. Tunneling piezoresistive effects of interlocked microdome structures fabricated using membrane filters with different pore sizes were observed. The measured maximum sensitivity and typical response time were approximately −7.73 kPa−1 and 4 ms, respectively. In addition, the measured results show that the patterned polymer composite arranged in a row–column array can effectively eliminate the crosstalk effect. Moreover, measurements for various tactile sensing applications were demonstrated.
Subjects
Carbon nanotube
Buckypaper
Tactile sensor
Supercapacitor
Vacuum filtration
Nylon membrane filter
Conductive polymer
Type
thesis
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