Miniature, low-cost, 200 mW, infrared thermal emitter sealed by wafer-level bonding

Infrared (IR) thermal emitters are widely used in monitoring applications. For autonomous systems, miniaturized devices with low power consumption are needed. We have designed, fabricated and tested a novel device design, packaged on the wafer level by Al-Al thermo-compression bonding. 80 mu m wide Aluminium frames on device and cap wafers were bonded in vacuum at 550 degrees C, applying a force of 25 kN for 1 hour. The bond force translated to a bond pressure of 39 MPa. Subsequent device operation showed that the seals were hermetic, and that the emitters were encapsulated in an inert atmosphere. The emitters were optimized for radiation at lambda = 3.5 mu m. Emission spectra by Fourier Transform Infrared Spectroscopy showed high emissivity in the wavelength range 3 -10 mu m at 35 mA driving current and 5.7 V bias, i.e. 200 mW power consumption. The emitter temperature was around 700 degrees C. The rise and fall times of the emitters were below 8 and 3 ms, respectively. The low thermal mass indicates that pulsed operation at frequencies around 100 Hz could be realized with about 90 % modulation depth. The measured characteristics were in good agreement with COMSOL simulations. Thus, the presented devices have lower power consumption, an order of magnitude higher modulation frequency, and a production cost reduced by 40 -60%(1-4) compared to available, individually packaged devices. The patented device sealing provides through-silicon conductors and enables direct surface mounting of the components.