Wafer-Level Vacuum Packaging of Micromachined Thermoelectric IR Sensors

In the trend towards low-cost, high-performance, and miniaturization, a wafer-level vacuum package is developed for micromachined thermoelectric infrared (IR) sensor. An IR sensor wafer and a cap wafer are bonded together in a vacuum chamber using Au-Au thermocompression bonding, where the cap wafer not only protects the floating thermopile structure but also selects IR light for the sensor. The device fabrication and Au-Au thermocompression hermetic bonding process as well as the packaged IR sensor characterization is presented in this paper. Experimental results show that the wafer-level vacuum packaged IR sensor has a four times higher responsivity and detectivity than the IR sensor with atmosphere pressure package, which confirms the IR performance improvement due to vacuum packaging. IR microscope image of the packaged device proved that the Au-Au thermocompression bonding process is compatible to the handling of fragile micromachined thermopile structure. Average leak rate and shear strength are, respectively, 3.9 × 10^-9 atm cc/s and 16.709 Kgf, which shows that the Au-Au thermocompression hermetic bonding is suitable for the wafer-level vacuum packaging of micromachined thermoelectric IR sensor.