Heterogeneous 3D integration for uncooled infrared bolometer arrays: (a) separate fabrication of ROIC wafer and handle wafer with resistive bolometer material; (b) adhesive wafer bonding; (c) thinning of handle wafer; (d) bolometer definition; (e) via formation; (f) sacrificial etching of polymer adhesive.

In the ICU project, heterogeneous three dimensional (3D) integration is used to integrate the infrared bolometers on the read-out-integrated-circuit (ROIC) wafer. In 3D bolometer integration, the bolometer materials are deposited on a separate handle wafer. The materials are then transferred from the handle wafer to the ROIC wafer using low-temperature adhesive wafer bonding in combination with sacrificial removing of the handle wafer as shown in Figure c. The achievable bolometer dimensions are identical to the ones made with conventional monolithic micromachining techniques. The advantage of 3D bolometer integration is that it allows the use of high-performance mono-crystalline temperature sensing bolometer materials on top of standard ROICs. Additional information on 3D IC integrated MEMS can be found here.