Photosensitive OTFT Array And Its Small-Signal Test

In some applied areas such as large area devices and flexible substrate, organic thin-film transistors (OTFTs) are better than inorganic semiconductor transistors, and they are considered to have broad application prospect. But the low carrier mobility of organic semiconductor materials makes the device’s response slow. It becomes the biggest problem hampering them practical application. For detecting the copper phthalocyanine (CuPc) thin film aluminum-gate static induction transistor which our research group prepared, we designed the weak current detection circuit, then test and analysis of its dynamic characteristics, to study the factors that affect the switching speed of the device. This circuit used the type OPA128J high precision op amp as the part of IV conversion. After the circuit assembly completed, we had made an actual test for its detection accuracy. The result is that current accuracy is 0.03nA, cut-off frequency is about 70kHz, and be up to the design requirements.In the course of the study, used of the detection circuit and resistor divider method to detect early samples of the device and the recently one, the dynamic characteristics of the both sample devices have been tested. Test results show that the early components response rise time for the rectangular wave is only 10ms, the rise time of the device recently is 268.1 ns. The device’s response time has obtained a larger increase. Use Keithley4200SCS semiconductor characteristics tester to test a variety of electrical parameters of the device. According to the measured electrical parameters, established a small-signal equivalent circuit to analysis the characteristics of the organic thin film static induction transistor, and the dynamic characteristics of the equivalent circuit have been simulated. The simulation results show that the small-signal equivalent circuit and the actual device can be a good fit, allowing in-depth analysis of the factors that affect the device performance. Then combination of organic semiconductor carrier transport mechanism and the semiconductor and metal contact theory, from the mechanism of device, we analysis the structure impact on the response rate, demonstrated that the vertical structure of the device can effectively enhance the response speed. And came to affect the device response speed of the two main factors: First, the transconductance of the device and second capacitance of gate– source and gate– drain.Based on above-mentioned studies, according to the research group’s test data about photosensitive characteristics of CuPc thin film transistor, and the classical principle of CCD image sensor array, we designed OTFT image sensor array, then the simulation for the dynamic characteristics of light-sensitive array. The simulation results show that the design can be applied to small-scale image sensors. But the actual production of such an organic photosensitive transistor arrays still wait for a breakthrough on Preparation.