Abstract
A novel wafer-level three-dimensional (3D) encapsulation structure was designed for radio-frequency microelectromechanical system (RF MEMS) infrared detectors and investigated by using the finite element method (FEM) simulation. A subwavelength structure with a circular array of coaxial apertures was designed to obtain an extraordinary optical transmission (EOT) on top of a silicon substrate. For perpendicular incident light, a maximum transmission of 56% can be achieved in the long-wave infrared (LWIR) region and the transmission bandwidth covered almost the full LWIR region. Moreover, the maximum transmission could be further promoted with an increase in the incident angle. The vertical silicon vias, insulated by inserted Pyrex glass, were used to generate electrical contacts. With the optimized structure parameters, a feed-through level lower than −82 dB, and a transmission coefficient of one single via of more than −0.032 dB were obtained at a frequency from 0 to 2 GHz, which contributed to the low-loss transmission of the RF signals. Due to the matched thermal expansion coefficients (TECs) between silicon and Pyrex glass, the proposed via structure has excellent thermal reliability. Moreover, its thermal stress is much less than that of a conventional through-silicon via (TSV) structure. These calculated results demonstrate that the proposed 3D encapsulation structure shows enormous potential in RF MEMS infrared detector applications.
Highlights
In recent years, uncooled radio-frequency microelectromechanical system (RF MEMS) infrared detectors, based on aluminum nitride (AlN) piezoelectric resonators, are attracting increased attention due to their small size, high performance, high thermo-mechanical coupling, high resolution, and complementary metal-oxide-semiconductor (CMOS) compatible process [1,2]
The results indicate that the silicon feedthrough has outstanding electrical performances feedthrough has outstanding electrical performances that are comparable to conventional through-silicon via (TSV), that are comparable conventional
The above results demonstrate that the proposed encapsulation structure has the ability to provide the ability to provide a high fidelity transmission of the RF signal for RF MEMS infrared detectors
Summary
In recent years, uncooled radio-frequency microelectromechanical system (RF MEMS) infrared detectors, based on aluminum nitride (AlN) piezoelectric resonators, are attracting increased attention due to their small size, high performance, high thermo-mechanical coupling, high resolution, and complementary metal-oxide-semiconductor (CMOS) compatible process [1,2]. RF MEMS infrared detectors put forward a higher demand for encapsulation, which is the major concern regarding their commercialization Several factors such as optical transmission, electrical interconnection, thermal stress, and vacuum sealing materials should be considered in particular to maintain their high performance after packaging. The film encapsulation can contribute to the miniaturization of devices, its micro-fabrication process is very complicated Another type is typically based on through-silicon vias (TSVs) and wafer-level bonding [8,9,10,11]. This work presents a novel wafer-level 3D encapsulation structure for RF MEMS infrared detectors that utilizes silicon feedthroughs to transmit electrical signals by inserting Pyrex glass as the electrical insulation and the anodic bonding material. The optical transmission, RF electrical transmission, and thermal stress were systematically studied by theoretical analysis as well as by using the finite element method (FEM) simulation
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