RF MEMS packaging based on LTCC technology and applications

Abstract

Low Temperature Cofired Ceramics (LTCC) has been a popular multi-layer ceramic (MCM) packaging material for many electronic applications. The main advantage with LTCC would be its ability to embed a major part of the electronic circuit within itself, apart from its enhanced RF functionality as against many lossy materials used. The advantages of LTCC in terms of frequency response, cost, ease of fabrication, etc. over many other packaging materials are presented. The applicability of LTCC as a packaging material, circuit mounting material, substrate material or a base material for micro devices is discussed. Low temperature co-fired ceramics (LTCC) is a key technology assets for MEMS/ MOEMS/RF-MEMS packaging. The tolerance of device alignment is the key issue of integration. In order to be able to use mass-manufacturing tools, the primary aim is to process 3D structures, such as, grooves, cavities, holes, bumps and alignment fiducials, which can be used for the passive alignment of devices. The tolerances of LTCC structures are typically ±5μm and in some specific cases ±2μm. Thermal management by the use of thermal vias in LTCC is a well-established technique, and liquid cooling channels in the LTCC substrate provide efficient additional means for high-power laser cooling. When targeting for thermally controlled systems, thermal bridge structures can be used to isolate critical devices from main structures. LTCC provides inherently hermetic substrate allowing for the possibility to hermetic encapsulation. Hermetic fiber feed throughs and transparent windows can be integrated in LTCC structures. Cavities, channels and sealed gas cells can be fabricated, also. RF antennas and coil structures for electro-magnetic field control can be integrated in the LTCC substrate. Therefore, 3D packaging of MEMS and RF MEMS is enabled by LTCC.