Pekka Rantakari

A 12 MHz micromechanical bulk acoustic mode oscillator

Abstract We demonstrate a bulk acoustic mode silicon micromechanical resonator with the first eigen frequency at 12xa0MHz and the quality factor 180xa0000. Electrostatic coupling to the mechanical motion is shown to be feasible using a high bias voltage across a narrow gap. By using a low-noise preamplifier to detect the resonance, a high spectral purity oscillator is demonstrated (phase noise less than −115xa0dBc/Hz at 1xa0kHz offset from the carrier). By analyzing the constructed prototype oscillator, we discuss in detail the central performance limitations of using silicon micromechanics in oscillator applications.

Square-extensional mode single-crystal silicon micromechanical RF-resonator

A micromechanical 13.1 MHz bulk acoustic mode (BAW) silicon resonator is demonstrated. The vibration mode can be characterized as a 2-D plate expansion that preserves the original square shape. The prototype resonator is fabricated of single-crystal silicon by reactive ion etching a silicon-on-insulator (SOI) wafer. The measured high quality factor (Q=130000) and current output (i/sub MAX/ /spl ap/ 160 /spl mu/A) make the resonator suitable for reference oscillator applications. An electrical equivalent circuit based on physical device parameters is derived and experimentally verified.

Micromechanical bulk acoustic wave resonator

We describe the use of bulk acoustic mode in micromechanical silicon resonators operating at radio frequencies. Based on measured data from the fabricated resonator (f/sub r//spl sim/14 MHz, Q>100 000) we analyze the characteristic impedance and signal levels in such microdevices and compare the values with conventional quartz crystals. We find that the high impedance level of microresonators can be met with integration of the readout electronics and that silicon can accommodate significantly larger vibration energy densities than quartz. Based on the results, we anticipate a wide application range for the micromechanical bulk acoustic wave structures in future wireless communication devices and microsensors.

Low noise, low power micromechanical oscillator

A 180-nm gap micromechanical resonator biased at 20 V and full custom integrated electronics are used to implement a 13-MHz oscillator that has noise floor of -147 dBc/Hz and power consumption of 240 /spl mu/W including both the loop amplifier and the buffer to a 10-pF load. The design of Pierce type MEMS oscillator is discussed in terms of noise, power, and oscillator stability.

Reducing the Effect of Parasitic Capacitance on MEMS Measurements

The use of micromechanical resonant structures in RF electronics possesses often a problem caused by a very low signal amplitude. In order to alleviate the influence of parasitic capacitance we propose here the use of the differential amplifier and demonstrate its use here on the processed electrostatically driven resonators. The component used in verifying the use of differential amplifier is a clamped-clamped beam resonator with Q=8000 and resonant frequency of f 0 = 12.3 MHz. A low-noise high input-impedance amplifier was used as a reference.

Low noise silicon micromechanical bulk acoustic wave oscillator

A 180-nm gap micromechanical resonator biased at 20 V and full custom integrated electronics are used to implement a 13-MHz oscillator that has noise floor of -147 dBc/Hz and power consumption of 240 µW including both the loop amplifier and the buffer to a 10-pF load. The design of Pierce type MEMS oscillator is discussed in terms of noise, power, and oscillator stability. Mixing of 1/f-noise is simulated and nonlinear electrostatic coupling is identified as a significant noise aliasing mechanism.

Silicon Micromechanical Resonators for RF-Applications

The small size and integrability make the silicon micromechanical rf-resonators attractive components for future wireless communication devices. In particular, we show that using the microresonators one can construct oscillators exhibiting low phase noise and good long-term stability. Such compact solutions challenge conventional quartz crystals in frequency reference applications.