A series of cyclic oligothienoacenes (1, 3, and 4) have been successfully synthesized through a stepped-cyclization synthetic strategy from tetra[3,4-thienylene] (2). Single-crystal X-ray diffraction analysis combined with theoretical calculations elucidated that the molecular configuration transforms from the saddle shape of 2 to the quasi-saddle shape (3b, 3c), then to the quasi-helical shape (4b), and at last to the quasi-plane shape (1, 3a, 4a). Organic field-effect transistors (OFETs) based on 1, 3a, and 4a were fabricated. The field-effect mobilities of 7.5 × 10, 2.6 × 10, and 6.8 × 10 cm V s were obtained for 1, 3a, and 4a, respectively. Compounds 3a and 4a can act as air-stable p-type organic semiconductors, while 1 is sensitive to the air.

Semiconductor temperature sensors have been widely used in medical, industrial, aviation and civil fields due to their advantages such as high sensitivity, small size, low power consumption and strong anti-interference ability. However, most Si-based temperature sensors are not suitable for the application in high-temperature environments. The new AlGaN/GaN heterojunction material not only has a wide band gap, but also has a high two-dimensional electron gas concentration and carrier mobility. Therefore, the device made with it not only has good electrical properties, but also can be applied in ultra-high environments. In this paper, a temperature sensor based on gateless AlGaN/GaN high electron mobility transistor structure was fabricated and its temperature-dependent electrical properties were characterized. The temperature dependence of current-voltage characteristics of the device were tested from 50 to 400 °C. The sensitivity of the device was studied as a function of the channel aspect ratio of the device. The stability of electrical properties was characterized after heating in air and nitrogen at 300—500 °C for 1 hour. The theoretical and experimental results show that as the aspect ratio of the device increases, the sensitivity of the device increases. At a fixed current of 0.01 A, the average sensitivity of the device voltage with temperature changes is 44.5 mV/°C. Meanwhile, the good high temperature retention stability is shown during stability experiments.