High resolution MEMS strain sensors for vibration detection on hard disk drive instrumented suspensions

As data densities in computer hard disk drives increase, airflow-induced vibration of the disk drive suspension becomes a major barrier to positioning the read-write head with sufficient precision. The overall system performance is limited both by the bandwidth of the position error signal and the positioning capability of the conventional voice coil motor.; Dual stage actuation has been proposed and implemented which utilizes an additional actuator on the suspension to achieve vibration compensation beyond the voice coil motor bandwidth. To fully exploit the dual-stage configuration, a dedicated sensor system is required on the suspension arm to detect vibration directly which enables high-frequency sampling and modal selectivity. The real time vibration information ensures better coordination between the two actuators resulting in higher efficiency and accuracy.; Using micro-electro-mechanical systems (MEMS) techniques, ZnO piezoelectric strain sensors are directly fabricated on silicon for characterization and on steel substrates, which is transformed into suspensions for testing. The sensors are intended to be used as point sensors for vibration sensing without putting extra burden on the host structures. An efficient method is used for identifying the optimal position and shape of the piezoelectric strain sensor on the steel suspension of a hard disk drive.; The experimental data indicate that the overall sensor system is capable of resolving better than 40.3 nano-strain time domain signal at frequencies above 2 kHz. The corresponding noise floor is lower than 200 femto-strain per root Hertz. The sensitivity, defined as the sensor voltage output over strain input, is calculated to be 340 V/&egr;. Micro ZnO piezoelectric sensors fabricated on steel hard disk drive suspensions also show excellent results. The sensor not only has a better signal-to-noise ratio but also detects more vibration information than the combination of two laser-Doppler-vibrometer (LDV) measurements in different directions.