Investigation of a unified LTCC-based micromachining and packaging platform for high density/multifunctional microsystem integration

Abstract

3D system-in-package has recently been considered a major enabler for high density and heterogeneous microsystem integration. We hereby proposed the concept of a unified micromachining and packaging platform based on LTCC (low temperature cofired ceramic) material system and process, which is implemented by first enhancing an existing LTCC hybrid IC fabrication line and then integrating different LTCC micromachining process modules one by one. Hence, the unified process flow can be accomplished within just one single package-test house. The platform has been capable of micromachining basic 3D MEMS (micro electromechanical system) microstructures into LTCC laminates and using them as a packaging substrate for mounting IC/MEMS from other process platforms, realizing self-contained and versatile microsystems of high density. The 3D microstructures formation process consisting of green tape machining, lamination and cofiring are demonstrated. The designing, analysis and fabricated samples of various micro functional structure enabled by the platform are illustrated, including embedded cooling microchannels (capable of lowering substrate temperature by more than 50K), microaccelerometer for harsh environment, micro Pirani gauge for in-situ vacuum level monitoring and THz (tera hertz) vacuum microelectronic devices. Samples of overall packaged MEMS and IC chips with micromachined LTCC substrate are displayed, showing ultra-low leakage (<; 5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> Pa·m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /s) vacuum packaging capability and significantly enhanced device performance. In addition, the platform has demonstrated the potential of stacking several laminates with mounted chips into a 3D frame-like microsystem. In comparison, 3D integration purely based on Si micromachining, e.g. anodic-bonding based in-situ wafer encapsulation, may only support a very limited spectrum of devices/materials and integration density and is somehow too expensive for many MEMS researchers.