Department of Electrical and Electronics Engineering
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Item Nanowire Impregnated Poly-dimethyl Siloxane for Flexible, Thermally Conductive Fan-Out Wafer-Level Packaging(IEEE, 2020) Benedict, SamathaFlexTrate TM , a flexible hybrid electronics (FHE) platform based on fan-out wafer level packaging (FOWLP) has demonstrated low die shift by using room temperature cured poly-dimethyl siloxane (PDMS) as a molding compound. In this paper, we investigate the enhancement of the thermal conductivity in PDMS used in the FlexTrate TM process to allow for better thermal management via microwave welding of commercially available copper nanowires dispersed in an uncured PDMS matrix, followed by a standard curing process. We also evaluate the thermal stability of PDMS, necessary if FlexTrate TM assemblies are to be used in conjunction with commonly used solder reflow processes, and show that PDMS is stable at standard reflow temperatures. Thermal conductivity enhancement using the microwave welding process is shown to be minimal, with a peak enhancement of ~40%.Item A High Spatial Resolution Surface Electromyography (sEMG) System Using Fan-Out Wafer-Level Packaging on FlexTrate™(IEEE, 2020) Benedict, SamathaWe demonstrate a fully integrated wireless surface electromyography (sEMG) system using Fan-Out Wafer-Level Packaging on a flexible biocompatible package with two corrugated high conductivity electroplated Cu wiring levels for efficient routing. The assembly has reliable performance under repeated flexing of >3000 times. The advanced Au capped Cu-based sensing electrode array architecture provides a high spatial resolution sEMG measurement with SNR comparable to standard Ag/AgCl electrodes, allowing for muscle activation signals to be recorded and transmitted wirelessly for off-line post processing. The system, which is compatible with our wireless charging system has a small form factor of 65 mm x 40 mm x 1 mm and light weight of <; 5 gm, making sEMG widely available outside the hospital setting.Item Heterogenous Integration of MEMS Gas Sensor using FOWLP : Personal Environment Monitors(IEEE, 2020) Benedict, SamathaThe exponentially increasing global population has led to environmental pollution which drastically affects human health; emphasizing the need for personal environmental monitoring. This demands the development of wearable devices capable of sensing the local environment and wirelessly transmitting data to cloud for spatial pollution tracking.In this paper, we have demonstrated the integration of MEMS gas sensors on flexible PDMS substrate using the fan out wafer packaging technique called FlexTrate™. One of the main issues in FOWLP involving the integration of MEMS sensors with a released membrane is the stability of the membrane during the molding process which results in poor yield. We have optimized the process for integrating released MEMS devices by protecting the membrane prior to the molding process and thus improving the stability of the released membranes and improving the yield by >80%. If the membrane is not protected, during curing the cavity which is filled by PDMS leads to membrane cracking due to generation of stresses. Simulation studies on the temperature profile of the microheater after protecting the membrane shows that the power consumption for 300 o C of heater temperature is 0.1W as compared to 0.091W where the PDMS fills the cavity of the membrane, which is <; 10% increase. Thus, this proves that the membrane protection process improves stability without affecting the thermal characteristics of the heater. Furthermore, there is an effort to integrate rechargeable flexible batteries to power the system wirelessly. Adding to this, is the capability of wireless communication achieved by integrating a Bluetooth die in the system to transmit data to a mobile phone.The MEMS sensors along with the other electronic components such as transimpedance amplifiers, analog-to-digital converters and Bluetooth will be integrated on the same PDMS platform with interconnect pitches of 40 μm.