Design of a Highly Efficient Broadband Silicon NIR-MWIR-LWIR Light Source Enabled by Phononic MEMS Technology

The high thermal conductivity of silicon has limited its use in thermal radiative devices where minimizing conductive cooling is a priority. Recent advancements in phononic MEMS technology enable a significant reduction in the thermal conductivity of electrically conductive nanowires, achieving extreme thermal isolation for semiconductor applications. This technology can lower thermal conductivity to a nanoWatt/K level approaching the dielectric limit. The nanowires are configured as phononic crystals which increase Bragg scattering of phonons, providing an extreme level of thermal isolation for application devices. This paper reports for the first time a highly efficient silicon broadband infrared light source based on phononic MEMS technology with emission in the near infrared (NIR) - midwave infrared (MWIR) – longwave infrared (LWIR) wavelength range. The thermal light source is fabricated from a starting silicon-on-insulator (SOI) wafer wherein a heated micro-platform and supporting nanowires are released from the surrounding substrate by removing the underlying SiO2 layer. The nanowires are configured with phononic crystal structure. The infrared source is an array of silicon pixels packaged within a vacuum cavity providing broadband infrared NIR-MWIR-LWIR radiation from micro-platforms. The device is called a light-emitting platform (LEP), which differentiates it from a narrowband LED emitter. LEP pixel radiative power efficiency within the vacuum cavity is over 90% with micro-platform temperature as high as 800 ˚C for silicon. The LEP efficiency compares with an Edison incandescent lightbulb at less than 10% for RGB light and 2.5% for uncooled LEDs emitting in the 2.3 µm wavelength range. Applications include MWIR floodlights, spotlights, vehicle headlights, biomedical stimulators, instrumentation light sources, etc.