Journal of the Korea Academia-Industrial cooperation Society (한국산학기술학회논문지)

The Korea Academia-Industrial cooperation Society (한국산학기술학회)
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The Interdigitated-Type Capacitive Humidity Sensor Using the Thermoset Polyimide

열경화성 폴리이미드를 이용한 빗살전극형 정전용량형 습도센서

  • 홍성욱 (가톨릭 관동대학교 전자공학과) ;
  • 김영민 (멤스칩 연구개발부) ;
  • 윤영철 (가톨릭 관동대학교 전자공학과)
  • Received : 2019.03.21
  • Accepted : 2019.06.07
  • Published : 2019.06.30
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Abstract

In this study, we fabricated a capacitive humidity sensor with interdigitated (IDT) electrodes using a thermosetting polyimide as a humidifying material. First, the number of electrodes, thickness, and spacing of the polyimide film were optimized, and a mask was designed and fabricated. The sensor was fabricated on a silicon substrate using semiconductor processing equipment. The area of the sensor was $1.56{\times}1.66mm^2$, and the width of the electrode and the gap between the electrodes were each $3{\mu}m$. The number of electrodes was 166, and the length of an electrode was 1.294 mm for the sensitivity of the sensor. The sensor was then packaged on a PCB for measurement. The sensor was inserted into a chamber environment with a temperature of $25^{\circ}C$ and connected to an LCR meter to measure the change in capacitance at relative humidity (RH) of 20% to 90%, 1 V, and 20 kHz. The results showed a sensitivity of 26fF/%RH, linearity of < ${\pm}2%RH$, and hysteresis of < ${\pm}2.5%RH$.

본 논문에서는 열경화성 폴리이미드를 정전용량형 습도센서의 감습재료로 사용하여 공정이 간단한 IDT(Interdigitated) 전극을 갖는 정전용량형 습도센서를 제작하고 특성을 측정 및 분석하였다. 먼저 일정한 용량값을 얻기 위하여 용량형 센서의 전극 수, 전극의 두께와 간격 및 폴리이미드 감습막의 두께 등을 최적화하여 마스크 설계 및 제작을 했으며, 실리콘 기판 상에 반도체 공정 장비를 이용하여 정전용량형 습도센서를 제작하였다. 제작된 센서의 면적은 $1.56{\times}1.66mm^2$ 이며, 전극의 넓이와 전극간 폭은 동일하게 각각 $3{\mu}m$, 센서의 감도를 위해 전극 수를 166개, 전극의 길이는 1.294mm로 제작하였다. 그런 다음 센서 특성을 측정하기 위해 PCB상에 패키징 하였다. $25^{\circ}C$ 챔버 환경에 센서를 삽입하고 LCR Meter에 연결하여 1V, 20kHz를 인가한 상태에서 20%RH에서 90%RH까지 습도변화에 대한 용량값 변화를 측정하였다. 제작된 정전용량형 습도센서의 측정 결과 감도는 26fF/%RH, 선형 특성 < ${\pm}2%RH$ 그리고 히스테리시스는 < ${\pm}2.5%RH$를 얻을 수 있었다.

Keywords

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Fig. 1. The key technologies of IoT

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Fig. 2. Schematic of capacitive humidity sensor

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Fig. 3. Schematic of IDT sensor Structure

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Fig. 4. Fabrication Process of the capacitive humidity sensor

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Fig. 5. Photograph of the capacitive humidity sensor

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Fig. 6. Fabrication Process of the capacitive humidity sensor

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Fig. 7. Schematic of the measurement system

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Fig. 8. Capacitance variation vs. relative humidity

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Fig. 9. The hysteresis of IDT capacitive humidity sensor

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