Joey Doll
PhD Candidate
Dept. of Mechanical Engineering
Stanford University

My Research I'm a PhD student in the Microsystems lab who develops scientific instruments for the study of touch and hearing at the molecular scale. One of the issues with studying these senses is that our bodies are very good sensors - far better than most of the tools that we use to probe them. For example, the hair cells in our ear which allow us to hear can sense forces at the piconewton scale, about the amount of force required to break a hydrogen bond.

The devices I developed are intended to bridge this technical gap. The main focus of my research has been designing and fabricating a better tool for studying the mechanics and kinetics of mammalian hair cells. Performance requirements include a spring constant of about 1 pN/nm, a resonant frequency of 20 to 200 kHz, pN-scale force resolution over that bandwidth and integrated on-chip actuation, all while operating in electrically grounded saline.

In order to achieve this level of performance I developed new methods for the design and thermal modeling of piezoresistive cantilevers. Next I integrated the sensors with on-chip piezoelectric (AlN) and thermal actuators and fabricated them in the Stanford Nanofabrication Facility. The resulting force probes are 300 nm thick, 1-2 microns wide and 30-200 microns long and are mass manufactured using standard silicon micromachining processes. The device and readout circuit are designed to allow simultaneous actuation and sensing, with -100 dB of actuator-sensor crosstalk rejection at 100 kHz. The force resolution of the piezoresistive sensors is within a factor of four of the noise floor set by Brownian motion.

Details of the thermal, mechanical and electrical design of the force probes can be found in my publications. My thesis and a book on piezoresistor design should be completed this summer, which will provide more details. We are currently using the final batch of probes to study mammalian hair cells and will publish additional papers on the probe design and fabrication shortly.

I'm currently looking for a position in industry or at a national lab. Here is my CV and resume. Miscellaneous Here are links to my Google Citations, photos, and personal website.