BS IEC 62951-2:2019 pdf download – Semiconductor devices – Flexible and stretchable semiconductor devices Part 2: Evaluation method for electron mobility, sub-threshold swing, and threshold voltage of flexible devices.
4.2 Test of electrical characteristics before bending The stability test of a flexible TFT is carried out using four kinds of biased evaluation. The negative-bias-stress (NBS) test is carried out witha VGs of -20 V at a fixed Vos of 10 V under dark and the substrate temperature is maintained at200Cand60C.The negative-biasillumination-stress (NBIS) test is carried out with a ‘Gs of -20 V at a fixed Vos of 10 V under ilumination with a white light-emitting diode of 300 cd/m2 brightness and the substrate temperature is maintained at 20 °C and 60 °C. The positive-bias-stress (PBS) test is carried out with a Vgs of +20 V at a fixed Vos of 0,1 V under dark and the substrate temperature is maintained at 20 0C and 60。C. The positive-bias-illumination-stress (PBIS) test is carried out with a ‘cs of +20 V at a fixed Vps of 0,1 V under ilumination with a white light-emitting diode of 300 cd/m2 brightness and the substrate temperature is maintained at 20°C and 60 °C.
4.3 Test of electrical characteristics under bending To characterize the effects of mechanical stress on flexible TFTs, strain is applied on the TFTs by bending the device convexly (i.e., inducing a tensile strain on the active devices) or concavely (i.e., inducing a compressive strain on the active devices) with varied radius of curvature R as shown in Figure 3. The bending direction is parallel or perpendicular to the drain-to-source current path. The TFTs are first bent to the maximum R for 1 min and then released to the flat state and are measured. This test cycle is repeated at decreasing R down to the minimum R. After each mechanical bending, the TFT on-current, the off-current and the gate leakage current are monitored.
The four kinds of test shall proceed under the bending state. To obtain the results of negative- bias-stress under the bending state (i.e., at different R), the NBS stability test is carried out with a VGs of -20 V at a fixed Vs of 10 V under dark, and the substrate temperature is maintained at 20 °C and 60 oC. The test of negative-bias-illumination-stress under the bending state is carried out with a VGs of -20 V at a fixed Vos of 10 V under ilumination with a white light-emitting diode of 300 cd/m2 brightness, and the substrate temperature is maintained at 20 °C and 60 °C. Under the mechanical bending state, the positive-bias-stress stability test is carried out with a VGs of +20 V at a fixed Vos of 0,1 V under dark and the substrate temperature is maintained at 20 0C and 60 °C. The value of positive-bias-illumination-stress under the bending state stability test is also carried out with a ‘Gs of +20 V ata fixed Vos of 0,1 V under ilumination with a white light-emitting diode of 300 cd/m2 brightness, and the substrate temperature is maintained at 20 °C and 60 C. 4.4 Test report The test report shall include the following elements: a) reference to IEC 62951-2; b) the layer materials including gate, insulator, active, source and drain of the tested device; c) test conditions: ●ilumination, in test case of NBIS and PBIS; ●gate and drain voltage; ●drain current; ●time under bending state; ●bending radius of the tested device; ambient temperature. d) test results: ●threshold voltage; ●sub-threshold swing.