Theory of gas-diffusion controlled sensitivity for thin film semiconductor gas sensor
Theory of gas-diffusion controlled sensitivity for thin film semiconductor gas sensor
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DOI：
10.1016/s0925-4005(01)00890-5
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发表时间：
2001-11-20
影响因子：
8.4
通讯作者：
Yamazoe, N
中科院分区：
文献类型：
--
作者：
Sakai, G;Matsunaga, N;Yamazoe, N
本文从理论上研究了气体输运现象对薄膜半导体气敏元件灵敏度的影响。假定可燃气体（目标气体）在薄膜中以努森扩散方式运动，与吸附氧的反应遵循一级反应动力学，建立了扩散方程。通过在稳态条件下求解该方程，推导出膜内的目标气体浓度作为距膜表面的深度（x）、努森扩散系数（D-K）速率常数（k）和膜厚度（L）的函数。由此获得的气体浓度分布允许估计定义为电阻比（R-a/R-g）的气体灵敏度（S），假设在深度x处的膜的薄层电导与那里的气体浓度成线性，具有比例常数（灵敏度系数）a。导出的方程表明，S随着L rootk/D-K的增加而S形地下降到1。此外，通过假设速率常数（k）和灵敏度系数（α）的温度依赖性遵循具有各自活化能的Arrenius型，可以导出涉及温度（T）的S的一般表达式。该表达式表明，当活化能选择适当时，S-T关系会产生一个火山形的关系，其高度随L的减小而增大。因此，基于该方程，可以相当好地模拟S在恒定T下对L的依赖性以及在恒定L下对T的依赖性。(C)2001 Elsevier Science B. V.保留所有权利。
Influences of gas transport phenomena on the sensitivity of a thin film semiconductor gas sensor were investigated theoretically, A diffusion equation was formulated by assuming that an inflammable gas (target gas) moves inside the film by Knudsen diffusion, while it reacts with the adsorbed oxygen following a first-order reaction kinetic. By solving this equation under steady-state conditions, the target gas concentration inside the film was derived as a function of depth (x) from the film surface, Knudsen diffusion coefficient (D-K) rate constant (k) and film thickness (L). The gas concentration profile thus obtained allowed to estimate the gas sensitivity (S) defined as the resistance ratio (R-a/R-g), under the assumption that the sheet conductance of the film at depth x is linear to the gas concentration there with a proportionality constant (sensitivity coefficient), a. The derived equation shows that S decreases sigmoidally down to unity with an increase in L rootk/D-K. Further by assuming that the temperature dependence of rate constant (k) and sensitivity coefficient (a) follows Arrenius type ones with respective activation energies, it was possible to derive a general expression of S involving temperature (T). The expression shows that, when the activation energies are selected properly, the S versus T correlation results in a volcano-shaped one, its height increasing with decreasing L. The dependence of S on L at constant T as well as on T at constant L can thus be simulated fairly well based on the equation. (C) 2001 Elsevier Science B.V. All rights reserved.