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Fabrication and Characterization of Suspended Microbridge Oxide Infrared Detector
|Authors: ||Yun-Jie Hsu|
|Contributors: ||NTOU:Department of Electrical Engineering|
Bolometer;responsivity;Fabry-Perot;temperature coefficient of resistance
|Issue Date: ||2011-06-22T09:06:40Z
|Abstract: ||本論文為了製作高吸收熱輻射的紅外線熱輻射感測元件，我們採用常見的光學諧振腔結構(Fabry-Perot)。以懸空的方式建構於矽基板之上，其懸空的目的是為了要避免熱敏阻型紅外線熱輻射感測元件(Bolometer)所吸收的紅外線輻射能量經由矽基板直接傳導而損耗。使用此懸空結構的氧化物材料熱容量較低，可以減少熱傳導，並可降低雜訊等效功率(NEP)。 我們採用鋁做為犧牲層，利用濕式蝕刻來定義鋁之圖形及釋放犧牲層。而紅外線感測材料上，考慮溫度電阻係數(TCR)值需越大越好以達到更強的訊號，所以選用了以重量比例27.5%導電氧化物及72.5%絕緣氧化物作為靶材，使用射頻磁控濺鍍系統在Si3N4/Si基板上沉積氧化物薄膜，薄膜成長時的溫度與壓力對於薄膜的形成有很大的影響，溫度與壓力太低或太高都不易形成狀態較好的薄膜，因此我們選擇了溫度120℃、壓力於1.6×10-2 torr的條件來成長薄膜，測量得到在室溫環境下300 K其TCR值為-1.3 %/K。 在元件特性量測方面，使用10 mW的氦氖雷射，遮光器(Shutter)頻率設定為0.1~10 Hz，元件的響應度(responsitivity)在0.1 Hz可達最大值1040.52 (V/W)，隨著遮光器頻率增加成線性遞減。根據上述量測獲得之響應度及雜訊電壓結果，可推知偵測率(D*)最大值為3.478x107 (cm-Hz1/2/W)。使用黑體爐量測其元件響應時間約為48.15 ms。 本實驗將所製作之熱影像感測元件進行初步測試。將光源利用透鏡聚焦後照在感測元件上，搭配讀取電路在電腦上讀出照光前後之電阻值，並轉換成影像。|
This paper is intended to present the design of an infrared thermal radiation sensor (Bolometer) capable of absorbing low- intensity infrared radiation. A Fabry-Perot optical resonant cavity structure is suspended over a silicon substrate to prevent the absorbed infrared radiation energy from depletion through direct conduction via the silicon substrate. Due to the low thermal capacity of the oxide materials and this suspended structure, both thermal conduction and the noise equivalent power (NEP) can be reduced. Aluminum is adopted for the sacrificial layer and wet etching is applied to define the established pattern on the aluminum as well as release the sacrificial layer. In choice of material for infrared detection, as a result of the consideration that the larger the TCR value the stronger the signals, 27.5% conductive oxide and 72.5% insulating oxide, in weight ratio, are used as the target for radio frequency magnetron sputtering to deposit the oxide thin film on the Si3N4/Si substrate. Both temperature and pressure have significant effects on the quality of the thin film. The quality of the thin film will be inferior if they are too low or too high. In consequence, temperature of 120 ℃ and pressure of 1.6×10-2 torr are discovered as the best conditions for the thin film formation. The TCR value measured in room temperature 300 K is –1.3 %/K. For device characteristic measurement, 10 mW helium-neon laser is used as light source with the shutter frequency set at 0.1~10 Hz. At 0.1 Hz, the maximum responsivity of the device achieves 1040.52 V/W, however it decreases progressively as the shutter frequency rises. Use blackbody radiation as heating source the response time of the device is about 48.15ms. Based on the above responsivity and noise voltage obtained from measurement, the maximum detectivity D* is deduced to be 3.478x107 (cm-Hz1/2/W). In this study, the thermal image produced by a preliminary array of 4x4 sensors. Light is focused through a lens and applied on the sensor. A readout circuit is attached to display the resistance before and after application of light and convert resistance changes into image on a monitor.
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