熱型微感測元件之熱參數測量

Abstract

獲得熱參數對於熱型微感測元件的功能評估十分重要,由此可以了解感測 之靈敏度及速度.本論文中以兩種不同的實驗方法,探求熱感元件之熱導與 環境氣壓關係,即:利用交流入射光求得的輻射計量法;與利用直流偏壓下 之熱能需求的直流電功率法.實驗的結果顯示,輻射計量法與電功率法所獲 得的數據在高度真空的條件下,相當吻合.但在接近大氣壓的範圍時,兩者 之一致性僅在高電功率的條件下方成立;低電功率的狀況下,直流偏壓所顯 示的熱導值則有明顯的增加與變異性.此結果顯示,在大氣中由於氣體熱流 的影響,以直流電功率法量度元件之熱導值必須謹慎考慮其準確性.又由兩 實驗方法的結果可一併求得熱感元件之熱容值與等效放射率.這些熱參數 的獲得,對於元件的熱傳物理的了解,以及電熱(Electro-thermal)SPICE模 擬程式的應用皆有相當的助益.此外本論文亦探討熱型微感測元件之截止 頻率時,定電流及定偏壓電路所獲得的電壓反應率皆具有一抑制之奇異點( Singularity),更高頻時則反常的增高,當外加之驅動功率越低時,此現象 越顯著. Obtaining thermal parameters of thermal microsensors is very important for evaluating the sensor performances. For example, thermal conductance of a thermal sensor is detrimental to its sensitivity. Two experimental methods are introduced in this report to study the relationship between the thermal conductance and the ambient pressure of a fabricated micro- sensor. The electrical power method which measures the balance heat required by the sensor under d.c. bias condition. The results of experiments show that, under high vaccum condition, the two methods have consistent thermal conductance. However, in the atmospheric regime the consistence appears only when the bias power is high. The measured conductance is obviously increased, owing to the gas-flow influence. It indicates that the measurement accuracy in the atmosphere with electrical power method must be carefully evaluated. In addition to the thermal conductanve parameter, the heat capacity and the effective emissivity can be derived from the two experiments. These obtained parameters are useful to the understanding of heat-transfer physics as well as electro-thermal SPICE simulation of thermal sensors. The high-frequency spectral responsity of a microbolometer is also investigated. Anomaly was observed when the input frequency is higher than the normal thermal cutoff frequency. Resposivity enhancement is prounced when the self-heating power of the bolometer is low. Interpretation of the abmormal effect is current under investigation in our laboratory.