超表面结构MEMS红外超窄带光源研究

Study on Metasurface Ultra-narrowband Infrared MEMS Light Source

针对常用的MEMS红外光源是类灰体光源,存在发射光谱范围比较广的问题,提出一种基于表面等离子体的超表面结构,将其覆盖在MEMS光源上实现一种有选择性、高发射率的窄带光源。还提出了一种改进的集总等效电路模型,通过模型能够比较准确地计算出超表面中结构尺寸对光源中心频率、带宽以及发射率的影响,探究了该结构中各个尺寸的改变对光源性能的影响。本文提出的模型计算结果跟仿真结果吻合,使用该模型能够避免耗时的、复杂的数值优化过程。

Devices which meet needs,low cost,miniaturization,low power consumption and so on,has become one of future research directions with the development of the Internet of Things. The development of MEMS technology has made infrared light sources take an important step in miniaturization and low power consumption. In gas sensors,chemical detection and other fields,infrared light sources are required to have a single frequency band,so that the component concentration sensitive to the corresponding wavelength can be identified more accurately. However,the commonly used MEMS infrared light sources are gray body light sources,which have a relatively wide emission spectrum and a relatively low emissivity.A narrow-band,high-emissivity light source can not only improve the sensitivity of detection,but also increase the photoelectric conversion rate and reduce power consumption. Recently the main method to improve the performance of MEMS infrared light source is to attach a layer of micro nano structure on the surface of the light source,which mainly includes nano-silicon structure,photonic crystal,grating,etc.Nano-silicon structure can significantly increase the emissivity,but its spectral distribution range is still wide. Due to their nonresonant nature photonic crystal emitters do not have very sharp bands or high emissivity and therefore do not significantly increase efficiencies. Grating can also achieve selective emission,however its bandwidth is slightly wider. To solve this problem,A metasurface structure based on surface plasmon is proposed in this paper. This metasurface is mainly composed of metal-insulatormetal,and the top layer is a layer of metal with a patterned cross structure. This structure has an electromagnetic resonance response to light,and the electrical response can be achieved by the fine metal periodic array on the top layer. And the size of the material structure can be designed to achieve a magnetic response to electromagnetic waves in the infrared band. When light propagates to the surface of this structure,a part of it will cause a collective oscillation of electrons and photons which is called surface plasmons. When the metasurface is covered on the MEMS light source,the electromagnetic waves of the same frequency propagated by the thermal radiation of the MEMS heating module will resonate and radiate in the metasurface and the electromagnetic waves of other frequency will be reflected by the underlying metal layer. A Narrowband light source with selectivity and high emissivity based on metasurface is made by this principle. Fortunately,the metasurface is perfectly compatible with current CMOS and MEMS processes. However,Previous models do not distinguish metasurface of different shapes so as to have no reference value to design the metasurface. So the design of metasurface is only determined by timeconsuming numerical optimization. To make the design more easily,An improved lumped equivalent circuit model is proposed in this paper,which base on the equivalent circuit theory and equivalent impedance theory. The response of the cross-shaped metasurface to light is converted into a circuit composed of resistance,inductance,and capacitance for analysis in this paper. And the circuit mainly includes the resistance,inductance,and mutual inductance and capacitance of the upper and underlying metals. The impedance of the model is analyzed to obtain the information of light frequency,bandwidth and so on according to the impedance matching theory of electromagnetic waves. Then the influence of the structure size on the center frequency,bandwidth and emissivity of the light source can be calculated accurately. The influence of the change of each size in the structure on the performance of the light source is explored by changing a single variable through the control variable method,and the influence of the change of the corresponding size in the model on the light source is also analyzed. The laws they reflect are basically the same. Using the model,A light source with a wavelength of 4 μm,an emissivity up to99.7%,and a bandwidth of only 87 nm is be designed. The emission spectrum calculated by the model is basically consistent with the simulation results,which proves the predictability of the model,and at the same time it is also testified time-consuming and complex numerical optimization can be avoid during design by using the model.