Hyo-Derk Park

A silicon-based flexible tactile sensor for ubiquitous robot companion applications

We present the fabrication process and characteristics of a 3-axes flexible tactile sensor available for normal and shear mode fabricated using Si micromachining and packaging technologies. The fabrication processes for the 3 axes flexible tactile sensor were classified in the fabrication of sensor chips and their packaging on the flexible PCB. The variation rate of resistance was about 2.1%/N and 0.5%/N in applying normal and shear force, respectively. Because this tactile sensor can measure the variations of resistance of the semiconductor strain gauge for normal and shear force, it can be used to sense touch, pressure, hardness, and slip.

Fabrication and Sensing Behavior of Piezoelectric Microcantilever for Nanobalance

The fabrication and analysis of a cantilever microtransducer were performed for a mass-detecting device. We designed piezoelectric microcantilever arrays with various lengths and shapes to investigate their resonance properties and sensitivity. Finite element method (FEM) simulation was carried out to estimate the resonant property of the microcantilever. A multilayered piezoelectric microcantilever has been successfully fabricated using micro-electromechanical systems (MEMS) processing. The microcantilever employs a sol-gel derived Pb(Zr0.52Ti0.48)O3 (PZT) capacitor fabricated on a low-stress SiNx layer. The microcantilever showed a natural resonant frequency of 16–26 kHz. The microcantilever exhibited a mass sensitivity of 34.1 Hz/ng, which enables its application to nanobalance, i.e., to detect biomolecules or gas molecules in a nanogram regime.

Gas Sensor Application of Piezoelectric Cantilever Nanobalance; Electrical Signal Read-Out

We have fabricated piezoelectric microcantilever transducer for a miniaturized gas sensor, to detect environmental gas molecules, i.e., volatile organic compound (VOC). The microcantilever consist of Pb(Zr, Ti)O 3 (PZT) capacitors and SiNx layer as an actuating and a supporting layer respectively. The fundamental resonant frequency of microcantilever was in the range of 17∼29 kHz. To measure the gas sensitivity, the microcantilever surface was coated with polymethylmetacrylate (PMMA), which is known to have sensibility for primary alcohols. The resonant frequency shift of the microcantilever was measured by complex impedance analysis, which only uses electrical signal output from the microcantilever. As the vapor concentration of the alcohol (ethanol or methanol) increased, the resonant frequency of microcantilever was linearly shifted toward the lower frequency range. The gas sensitivity of microcantilever was 0.03 Hz/ppm for methanol vapor.

Characterization of Sol–Gel Multicoated Thick Pb(Zr0.52, Ti0.48)O3 Films on Platinized Silicon Substrates for Microdevices Applications

The microstructures and electrical properties of thin and thick Pb(Zr0.52, Ti0.48)O3 (52/48 PZT) films for microdevice applications with thicknesses from 480 nm to 2.3 µm on 350 nm Pt(111)/40 nm Ti/300 nm SiO2/Si 525 µm substrates fabricated by a sol–gel multicoating process were investigated. These PZT films showed dense and homogeneous surface microstructures. The crystalline structures of 480-nm-thick PZT films showed a (111) preferred orientation over (100), (200) and (110) orientations. The intensity ratios of (100) and (200) to (111) increased at PZT film thicknesses greater than 480 nm. By Auger electron spectroscopy, small-composition-variation peaks at an interval of approximately 120 nm at interfaces produced by each PZT coating process of 480 nm PZT films were found. Dielectric constants increased from 825 to 880 at 100 kHz and PZT film thicknesses from 480 nm to 2.3 µm. The Pr and Ec of 2.3-µm-thick PZT films were about 30 µC/cm2 and 58 kV/cm, respectively. The e31,f of 1-µm- and 2-µm-thick PZT films was characterized by the fabricated e31,f measurement system before and after poling.

Fabrication of Polymer-based Flexible Tactile Sensing Module with Metal Strain Gauges and Interconnecter

We present fabrication of flexible tactile sensing module with NiCr strain gauge as sensing element and interconnecter for signal treatment by polymer MEMS (micro electro mechanical system) technologies using polyimide materials. The tactile sensor array is composed of 16 times 16 sensing elements with 2 mm times 2 mm cell size and its overall size is 4 cm times 5 cm. Both the tactile sensor array and interconnecter are placed in the sensing module during the fabrication process. The fabricated tactile sensing module is measured continuously in the normal force range of 0~1 N with tactile sensor evaluation system. The variation of resistance is relatively increased linearly in the range of 0~0.6 N and saturated after 0.6 N. The variation rate of resistance is approximately 3%/N in the linear range. In addition, the flexibility of the sensing module is adequate to be placed on any curved surface like cylinder because the matrix consists of polymer and metal thin film.

PIEZOELECTRICALLY DRIVEN MICROTRANSDUCER MASS SENSORS

ABSTRACT Various types of piezoelectrically driven microtransducers which have a similar physical dimension, i.e., microcantilever, microdiaphragm and microbridge, were fabricated by micro electromechanical system (MEMS) technique and are compared on the mass sensing behavior. The diol based sol-gel derived Pb(Zr0.52,Ti0.48)O3 (PZT) thin film capacitors were integrated for the piezoelectric actuation. We have used the resonant frequency change of microtransducer upon mass increase as a sensing mechanism. The resonant frequency of the microtransducer was measured by analysis of electrical signals from microtransducer such as impedance, capacitance, phase and dielectric loss. The fundamental resonant frequencies of the microcantilever, microbridge and microdiaphragm with similar dimension (∼300 μm) were about 26 kHz, 260 kHz and 290 kHz, respectively. The mass sensitivities of bare microtransducers were measured by metallic thin film deposition and analysis of spectral responses from microtransducers. When various microtransducers are compared, the microcantilever exhibited the highest gravimetric sensitivity factor (Δf/Δm×f0 = 694.4 cm2/g), followed by the microbridge and microdiaphragm. However, the microbridge showed the highest mass sensitivity (Δf/Δm = 137.5 Hz/ng) among those transducers.

Fabrication of capacitive absolute pressure sensor using Si-Au eutectic bonding in SOI wafer

A capacitive absolute pressure sensor was fabricated using a large deflected diaphragm with a sealed vacuum cavity formed by removing handling silicon wafer and oxide layers from a SOI wafer after eutectic bonding of a silicon wafer to the SOI wafer. The deflected displacements of the diaphragm formed by the vacuum cavity in the fabricated sensor were similar to simulation results. Initial capacitance values were about 2.18pF and 3.65pF under normal atmosphere, where the thicknesses of the diaphragm used to fabricate the vacuum cavity were 20 µm and 30 µm, respectively. Also, it was confirmed that the differences of capacitance value from 1000hPa to 5hPa were about 2.57pF and 5.35pF, respectively.

Piezoelectrically Driven Self-Excited Microbridge VOCs Sensor

Piezoelectrically driven microbridge gas sensors have been fabricated by MEMS process. We have used the resonant frequency change of the microbridge transducer upon mass increase. The sol-gel derived Pb(Zr0.52,Ti0.48)O3 (PZT) film capacitor as an actuating part was integrated into the thin SiN x bridge structure. The resonant frequency of the microbridge was in the range of 250 kHz to 260 kHz. The microbridge exhibited a mass sensitivity and gravimetric sensitivity factor of ca. 7.27 pg/Hz and 345 cm 2 /g, respectively. With the PMMA polymer sensing layer, the microbridge showed the gas sensitivity of 1.67 ppm/Hz for ethanol vapor.

Trends in recent sensor technology using nano materials-Review

최근 인류의 삶의 질 향상에 따라 건강하고, 쾌적하고, 편안한 삶을 살기 위한 많은 노력이 진행되고 있다. 센서는 이 러한 삶의 질 향상을 위해서 필수불가결한 요소 중 하나이며, 고성능의 지능화된 센서가 요구되고 있어, 앞으로 이에 대 한 수요는 더욱 증대될 것으로 생각된다. 최근의 센서 연구 개발 방향은 센서에 기능을 부여하는 기능성 재료가 중요한 요소로 더욱 부각되고 있으며, 특히, 다양한 성분과 형태로 존재하는 나노 기능 재료는 기존의 벌크 재료와는 차별화된 독특한 물리, 화학, 기계, 광학적 특성을 갖고 있어 더욱 주목받고 있다. 최근 기존의 나노 입자 연구에서 더욱 발전하여 센서로 적용하기 위한 나노선이나 CNT를 포함한 나노튜브, 나노 복합재료 등의 연구가 매우 활발하다. 본 논문에서는 이 러한 나노 재료를 이용한 가스 센서, 수질 센서, 바이오 센서, 광 센서 그리고 물리 센서 등 최신 나노 센서 연구개발 동 향을 살펴보았으며, 미래 센서기술 발전방향 중 하나로서 나노 재료에 의한 센서의 고기능화 및 극소형화가 매우 중요한 부분으로 활용될 것으로 예측되었다.

Gas Sensors Based on Piezoelectric Micro-Diaphragm Transducer

ABSTRACT We have fabricated high sensitive gas sensor based on piezoelectrically driven micro-diaphragm transducers. The micro-diaphragm transducer was fabricated using micro-electro-mechanical-system (MEMS) technique. The diol based sol-gel derived Pb(Zr0.52,Ti0.48)O3(PZT) film was used as a piezoelectric actuating layer. We have used the resonant frequency change of micro-diaphragm transducer upon mass increase as a sensing signal. The resonant frequency values were measured by analysis of electrical signals from the micro-diaphragm transducer. The fundamental resonant frequency of the micro-diaphragm was in the range of 250 to 360 kHz, depending on their physical boundary conditions. The mass sensitivity of bare micro-diaphragm transducer was 66.5 Hz/ng. Two polymer sensing layers such as the polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) films were used to estimate the gas sensing behavior of microtransducers for various vapors of organic compounds. PMMA was used to detect primary alcohols while PDMS was used for toluene and benzene. The resonant frequency of micro-diaphragm transducer was shifted toward lower frequency range as the vapor concentration increased. With PMMA gas sensing layer, the micro-diaphragm showed a gas sensitivity of 0.456 Hz/ppm for ethanol vapor. When the PDMS gas sensing layer was used, the micro-diaphragm showed a gas sensitivity of 0.143 Hz/ppm for toluene vapor. When the test vapors were removed from the reaction chamber, the resonant frequencies of micro-diaphragm sensors were completely recovered to their initial state.