This dissertation presents a platform structure fabricated from silicon wafers that, once assembled, forms a three-dimensional (3-D) structure that fully houses a microsystem containing sensors and the necessary system electronics including the power supply. The unique design of this platform provides a supporting package in a 3-D form factor, as well as routing capabilities with orthogonal mechanical and electrical connections between the assembled internal sides.
Two different mechanical connector types are investigated to aide in assembly: (i) Hook-Hole snap lock features; and (ii) interdigitated teeth. Both connection types are analyzed to characterize structural strength and identify optimal platform sizes. The results indicate that, under simulated pressures and forces, the platform mechanical strength is enhanced nearly three to five times depending on the connector type. Furthermore, the mechanical strength is orders of magnitude greater for smaller platform sizes.
An example platform is fabricated to realize an autonomous data-logging inertial measurement unit. The unit consists of a programmable microcontroller, Flash memory, a three-axis accelerometer and a three-axis gyroscope. Double-sided polished, 250 µm-thick, (100) and (111) silicon wafers are processed using standard microfabrication techniques to produce the individual platform pieces. The platform pieces are manually assembled and incorporate out-of-plane, orthogonal solder joints to enable stable mechanical and electrical connectivity between the individual platform pieces.
Sensor data, at a rate of 100Hz, is collected via a microcontroller and stored in the on-board flash memory. The platform is mounted on a two-degree-of-freedom rotational stage and manually rotated in 90° increments such that the sensor’s x, y and z-axes experience +1g and/or -1g accelerations. The platform structure can collect reliable and repeatable inertial data. The system electrical properties are characterized including the maximum power consumption of ~16 mW and the duration of data-logging capability which is ~48 hours.
It is envisioned that extensions of this 3-D platform, combined with standard microfabrication techniques, will enable the integration of a variety of heterogeneous materials and devices with a form factor that reduces planar footprint and expands 3-D design space. Through-wafer vias can be used to electrically connect devices fabricated into both wafer surfaces or assembled on these surfaces.