Contact-based and proximally thermosensitive few-layer graphene Ntc thermistors with highly fast switching behavior

Official URL: https://dx.doi.org/10.1002/aelm.202300723

Patterning graphene onto polymeric materials offers benefits in realizing flexible, stretchable, and wearable multifunctional electrodes. However, the employed integration approaches and use of non-patternable polymers hinder the patterning of graphene at the sub-millimeter (mm) scale. Serpentine-shaped thermally active graphene patterns (thermistors) of 500 × 500 µm2 area are reported by the seamless integration of chemical vapor-deposited graphene (GCVD) into readily available SU-8 polymer with MEMS-compatible cleanroom fabrication processes. The thermistor resistance decreases with an increase in graphene temperature changed by local heat conduction or environmental thermal radiations; hence, exhibits a negative temperature coefficient (NTC) of resistance of 0.0012/°C. Furthermore, very fast resistive switching with 1 s response and 3.2 s recovery time is observed under cyclic heating and cooling. Several application scenarios including, monitoring of surface temperature (e.g., kettle and human body), rapid response (0.25 s) to heat conduction and radiations (0.5 s) from human finger at room temperature for contact and touch-free proximity switching (e.g., turn ON and OFF an LCD display) are demonstrated. Moreover, owing to its small area less than a ceramic resistor enabled to integrate the fabricated thermistor onto a printed circuit board (PCB) to construct a fully packaged thermometer to monitor ambient temperature.