The Development Of A Fingertip Implantable Mems Tactile Sensing System
This thesis explores the development of a fingertip implantable MEMS tactile sensing system to provide tactile sensing capabilities for paralyzed people using a brain machine interface (BMI) technology. With BMI-controlled stimulation, paralyzed people are able to restore hand movement with their native hand without sensation. However, sensory feedback for these BMI-controlled stimulators is still missing. To overcome this barrier, development of a tactile sensing system is necessary. In previous studies, multiple approaches have been exploited to realize fingertip tactile recognition for wearable electronics, prosthetics, and robotics. Compared with these existing tactile sensors with wearable devices or robotic arms, we are interested in combining tactile sensing with implantable MEMS technologies. With this purpose, our goal is to build an implantable tactile sensing system with wireless power and signal transmission capabilities to provide somatosensory feedback in an improved BMI system. One of the most important factors in a successful biomedical MEMS implant is the biocompatible package. In this work, a fused silica package with good hermeticity to moisture, biocompatibility, CMOS compatibility, as well as multiple feedthroughs for electronic access was developed and characterized. A localized fusion bonding technology based on carbon dioxide (CO2) laser assisted machining was proposed to achieve simultaneous bonding and dicing of fused silica wafer stacks, while maintaining temperatures inside the package sufficiently low that electronics are not damaged. To demonstrate an implantable tactile sensor, a capacitive force sensing technology based on the packaging technology was developed to satisfy hermetic and biocompatible requirement for implantation applications. The performance of this tactile sensor is investigated with quantitative static and dynamic loading measurements. In addition, both an in vitro study with the sensor embedded under a skin-phantom, and an in vivo study with implantation of the sensor in a monkey hand are examined. Successful experimental results verify the feasibility of the sensing technology. To further develop an implantable tactile sensing system with wireless communication capability, a multilayer fused silica structure incorporating the capacitive force sensor, an ASIC for wireless power and data communication, and the hermetic package technology for encapsulating the electronics is fabricated. The development of an inductive coil integrated with the system both for energy harvesting and wireless data transmission was presented and fabrication process of the system is discussed. To characterize the tactile sensing system, a customized experimental setup is employed and static loading measurement with dynamic loading analyzer is performed verifying that both the pressure sensing and wireless transmission of the system are functional. This wafer level technology will be very useful for other implantable pressure sensing and micro-opto-electro-mechanical systems (MOEMS) applications.