Temperature stability is a key to the successful integration of numerous components, including filters and resonators, in wireless and other designs. For example, surface-acoustic-wave (SAW) devices offer superb selectivity, although with performance highly dependent on temperature. For this reason, some designers have sought filters based on alternative technologies, such as larger ceramic filters or more expensive film-bulk acoustic resonator (FBAR) devices. Fortunately, for those in need of the small size, low cost, and high performance of SAW filters (and resonators), Ziptronix (Research Triangle Park, NC) provides a solution in the form of engineered substrates: the company's unique, covalent bonding process yields piezoelectric and other substrates that can be bonded to carriers such as glass for enhanced temperature stability.

Founded in 2000, the company uses its proprietary ZiROCâ„¢ covalent bonding technology at room temperature to perform wafer-to-wafer bonding and die-to-wafer bonding on 4-to-8-in. wafers. The covalent bonding process includes precise polishing of the materials to be bonded to form two materials into one with high bond energy between the two material components. The non-adhesive process is performed at room temperature, without the high processing temperatures that can be destructive to some sensitive semiconductor die and surface-mount components.

Compared to fusion-bonding or anodic-wafer-bonding processes, the ZiROC process is performed at room temperature to create low-stress bonds and materials with minimum defects and low thermal resistance. The process can bond materials with different coefficients of thermal expansion (CTE), supports standard through-bond processing, and enables multilayer circuitry using a three-dimensional interconnect topology.

The company has applied its revolutionary process to create a "standard" line of substrates aimed at developers of SAW filters and oscillators (see figure). Each of these temperature-compensated SAW substrates is actually a wafer pair consisting of a low-cost piezoelectric material, such as lithium tantalite and lithium niobate, bonded to glass, quartz, or other base wafer with low CTE. The resulting engineered wafer exhibits the electrical properties of the piezoelectric top wafer layer with the thermal stability of the base substrate. These new materials will enable designers to create temperature-stable piezoelectric-based components for a variety of functions in communications systems, including resonators, oscillators, and filters. Ziptronix, Inc., Research Triangle Park, NC; Internet: www.ziptronix.com.