VHF microelectromechanical mixer-filters

The recent high demand for portable, low power communication systems has spurred rapid and explosive growth in the area of wireless communications. In conjunction with the issues of lower cost and lower power, portable system manufacturers are also looking into miniaturization of these systems. Efforts to miniaturize such hand-held portable systems is also cater to the convenience and fashion sense of consumers. In the majority handsets today, the active electronics, such as the amplifiers, drivers (i.e., buffers), and baseband signal processing circuits, can be directly integrated on a Si or GaAs substrate. However, many of the components needed in a communication system, such as the surface acoustic wave (SAW) and ceramic filters, and crystal oscillators, are off-chip bulky components, that must be interfaced with the chip-level electronics on the board level. This presents a major bottleneck against miniaturization of the system. Moreover, because these components must interface with the electronics on a board level driver circuits are often needed to impedance-match the chip-level electronics to the external components in order to prevent passband. These driver circuits tend to consume large amounts of power.; This research investigates the possibility of substituting these off-chip modules with equivalent on-chip microelectromechanical (MEMS) versions, with the intention of reducing power, cost, and size. These MEMS-based devices consume zero do power, are largely compatible with integrated circuit (IC) technology, and require orders of magnitude smaller area and volume than their macroscopic counterparts. The first part of this research work focuses on the design and performance of VHF range spring coupled clamped-clamped beam micromechanical (μmechanical) resonators and filters, operating from 10MHz to 70MHz. Current micromachining technology has demonstrated the performance and reliability of these mechanical vibration-based devices from the LF range of 20kHz up to about the mid VHF range of 70MHz, with Quality factors ( Q's) ranging in the tens of thousands. These results suggest that perhaps these devices can ultimately reach the UHF range of about 1GHz, which is needed for wireless applications, with proper mechanical designs and appropriate structural materials. Localized annealing and voltage-based passband tuning techniques required for proper filter operation under non-ideal environments will also be presented.; The second part of the research focuses on utilizing spring coupled filters to perform low-loss frequency translation (i.e., mixing) and highly selective filtering of applied electrical input signals. In particular, successful downconversion of RF signals from 40MHz to 200MHz and subsequent filtering from 27MHz to 35MHz IF with less than 15dB of combined mixing conversion and filter insertion loss has been demonstrated using this single μmechanical device.; The final part of this thesis introduces a technology that demonstrates the use of cold compression bonding to modularly combine platform-supported μmechanical resonators and filters with integrated BiCMOS transistor circuits to form a microsystem. This technology adopts an approach very much similar to Multi Chip Modules (MCM's) commonly used for microprocessors. The MEMS and transistors are built on separate wafers, thus, allowing a completely modular, wafer-scale batch process. Using this process, functional platform-mounted clamped-clamped beam μmechanical resonators and filters with center frequencies up to 40MHz have been demonstrated.