Thermal sensing performances under mild temperature conditions. (a) Transfer (inset: output) curves according to the temperature by heat sources (TA = 25~70 °C) at VD = -20 V and VG = -20 V. (b) Drain current (ID) response according to the distance between the load-like heaters and the flexible PDLC-i-OFET devices. (c) Net drain current change (ΔID) as a function of temperature (TA): The dashed line was fitted with the power-law equation (ΔID ~ TA α) (note that more than sixteen devices were measured).
Full size image
In order to examine the response time, the distance between the heat sources and the flexible PDLC-i-OFET devices was controlled to change between 3 mm and 50 mm. As shown in Fig. 5b, the drain current at VG = -5 V and VD = -1 V was quickly increased as the heat sources approached the PDLC layers of devices for all the temperatures tested in this work. When the heat sources were moved out of the devices, the fast decay in drain current was measured. Here it is worthy to note that the different response between approaching (rise time = ~2.2 s) and receding (decay time = ~8.4 s) of the heat sources can be attributable to the different thermal cycle of heating and cooling for the flexible PDLC-i-OFET devices. Interestingly, as shown in Fig. 5c, the change of peak drain current (ΔID) as a function of approaching temperature (TA) was well fitted with a power-law type equation (ΔID ~ TAα, where α is an exponent).