Characterization of On-Foil Sensors and Ultra-Thin Chips for HySiF Integration

The characterization of multiple mechanically flexible passive and active electronic components, namely on-foil temperature sensor, relative humidity sensor, and ultra-thin microcontroller unit (MCU) integrated circuit (IC) is presented. These components are readily available for Hybrid System-in-Foil (HySiF) integration, which combines the merits of the high-performance silicon chips with the large-area electronics. The 60-nm thin-film resistance temperature detector (RTD) is fabricated on different substrates and the extracted temperature coefficient ranges from 0.002 to 0.003(Ω/Ω)/°C. Furthermore, the capacitive relative humidity sensor is fabricated by utilizing a polymeric sensing dielectric material that is compatible with those polyimides used in ultra-thin chip embedding. The 1-μm thick sensor achieves a fast adsorption rise time of 54 ms and a spontaneous desorption fall time of 750 ms. For flexible ICs packaging and HySiF integration, microcontroller chips are back-thinned to a thickness of about 30 μm. The characterization of the MCU after the thinning process step showed undegraded performance of the integrated analog-to-digital converter in terms of linearity. However, a drop in the on-chip temperature sensor sensitivity is observed for the thin chips and significant degradation in the period jitter of the high-frequency RC oscillator is measured. Finally, continuity tests are performed to validate the functionality of the ultra-thin MCUs when embedded using the Chip-Film Patch (CFP) flexible package.