大规模电阻阵红外景象产生器件的像素设计研究

Pixel design of large-scale resistor array infrared scene projector

电阻阵作为一种动态红外景象产生器件,在红外半实物仿真领域有着重要的应用。电阻阵可实现的规模与性能与红外微辐射像素列阵的设计有着密切的关系。文中从应用系统对大规模电阻阵器件的要求出发,结合电阻阵的工作原理,提出了像素驱动电路与MEMS结构一体化的设计方案,设计了规模可拓展的高占空比像素结构。通过采用高消光系数材料以及光学谐振腔结构,微辐射元的中波红外和长波红外的表面发射率达0.7。热力学仿真表明,通过合理的薄膜厚度和结构设计,微辐射元阵列的占空比达到51%,升、降温的热响应时间均小于5 ms,0.6 mW功率驱动下应力翘曲小于300 nm,长波红外表观温度可达582 K,中波红外表观温度可达658 K。结合设计方案提出了工艺制备方案,并通过小阵列流片初步验证了设计方案的可行性。该设计研究为国产大规模、高占空比电阻阵的研制指明了方向。

Objective As an infrared scene projector,the resistor array device played an important role in hardware-in-theloop infrared simulation system.Due to the emitted infrared image similar to the real target,it can generate dynamic infrared scene for infrared detectors.Usually,the scale of the infrared detector was 512×512 or 640×480,meaning the scale of the target simulator should be four times larger to ensure high-quality simulations,and developing a 1024×1024 scale resistor array device is necessary.The pixel design is the basis of resistor array and it determines the achievable scale and performance of the resistor array.Therefore,a pixel array that can be scalable to 1024×1024,can operate at 200 Hz,and has an apparent temperature close to 600 K must be achieved.For this purpose,a design scheme for integrating the pixel driving circuit and MEMS structure was proposed,and a scalable high-fill-factor pixel was designed in this paper.Methods A pixel circuit operating in snapshot mode was designed according to the functional requirements of the resistor array device(Fig.2).By investigating the design scheme for integrating the pixel driving circuit and MEMS structure,four key factors influencing the pixel performance were deduced,including fill factor,thermal conductance,heat capacity,and surface emissivity.Using the high extinction coefficient materials and an optical resonator structure,the surface emissivity of the micro emitter in mid-wave infrared and long-wave infrared reaches 0.7(Fig.5).Through proper film thickness design and geometric structure design,the fill factor of the micro emitter array reaches 51%(Fig.4).The thermodynamic simulation was used to assist the design of the micro emitter and evaluate its performance(Fig.6).A MEMS fabrication process was proposed to prepare pixel array sample(Fig.8).Results and Discussions The thermodynamic simulation results of the designed pixel show that the apparent temperature of mid-wave infrared and long-wave infrared at 0.6 mW power drive reaches 658 K and 582 K,respectively(Fig.7).The thermal response time for both heating and cooling is less than 5 ms,meaning the pixel can work at 200 Hz.The displacement of the emitter is less than 300 nm,which benefited from the geometry structure and the materials applied.The 640×410 array sample showed excellent geometry uniformity(Fig.9).The sample pixel was tested in air at 0.6 mW power drive and showed a long-wave infrared apparent temperature of about 400 K.The image result of this sample proved that the pixel design was achievable and functional(Fig.10).Conclusions Aiming at the requirements of developing large-scale resistor array devices,a design scheme for integrating the CMOS driving circuit and the MEMS structure into the pixel was proposed.The pixel driving circuit can work in snapshot mode.Benefiting from the MEMS structure,the fill factor of the micro emitter reaches 51%,which is much higher than that of the traditional resistor array.The thermodynamic simulation results showed that the radiation efficiency of the designed pixel was sufficiently high and capable of being applied in 1024×1024 resistor array device design.An array sample was fabricated using the proposed MEMS process.The test result of this sample proved the pixel design is achievable.The design research indicates the direction for developing domestic large-scale and high-fill-factor resistor array devices.