Lijuan Zhen

Organic thin-film transistor memory with gold nanocrystals embedded in polyimide gate dielectric

An all-organic memory device based on a copper phthalocyanine (CuPc) thin-film transistor (TFT) using gold nanocrystals embedded in a polyimide gate dielectric is demonstrated. Both the gate dielectric and the active semiconductor layer are organic materials. Discrete gold nanocrystals are adopted as the charge storage medium. Under proper gate bias, gold nanocrystals are charged and discharged, resulting in the modulation of the channel conductance. Current–voltage (I–V) measurements at room temperature show the memory behaviour of the fabricated devices. The detailed programming and erasing operations are discussed. Low fabrication temperature and low cost are two benefits of the fabricated memory devices, which could provide a low-cost solution for the all organic circuits.

Light-induced hysteresis characteristics of copper phthalocyanine organic thin-film transistors

Applying a bidirectional sweeping gate voltage, the white-light illuminated copper phthalocyanine thin-film transistors (CuPc-TFTs) show obvious hysteresis effect and the hysteresis window is 32 V. This effect is dominated by the additional carriers generated by photoirradiation. Although small hysteresis exists in CuPc-TFTs without illumination, light makes the hysteresis more obvious. Thus, CuPc-TFTs are promising to realize light detection and/or light memory in a single organic device for future low-cost, ultrahigh-density organic photoelectric integration.

Detecting the interface state of organic thin-film transistors through hysteresis characteristics

Under white-light irradiation, thin film transistors based on copper phthalocyanine (CuPc) exhibited obvious hysteresis effects when applying bi-directional sweeping gate voltage, the hysteresis window comes up to 32 V. This hysteresis effect is the result of those accumulated photogenerated carriers trapped in the interface, which proposed a feasible way to detect the state of the interface between organic functional materials and the dielectric layer.

Bilayer organic field-effect transistors (OFETs) with better stability

Double active layer OFETs were fabricated, based on two-step vacuum-deposition process. Pentacene deposited at room temperature acted as the active layer, and subsequently, CuPcs was deposited above the pentacene which acted as a protecting layer for the active layer. Due to the same electrical characteristics but different morphology, the bilayer structure was effective to decrease the contamination of impurity and gas, and then improved the devices stability in the air environment.

Reducing threshold voltage of organic field-effect transistor by using ZrO 2 /PMMA as gate dielectric

By depositing a PMMA (poly(methyl methacrylate)) layer on top of an evaporated layer of ZrO2, the leakage has 4 orders of magnitude reducing compared with bare ZrO2 layer. Low roughness of PMMA/ZrO2 surface produces a high quality interface between the organic semiconductor and the combined insulator, thus the device has a significant improvement in performance. The typical field effect mobility, on/off current ratio, and sub-threshold slope of OFETs with bilayer dielectric are 5.6×10-2 cm2/Vs, 1.2×103, and 0.3 V/decade respectively. It is noticeable that the threshold voltage is only 0.1 V.

Copper phthalocyanine thin-film transistors with polyimide as dielectric

Copper phthalocyanine (CuPc) thin-film transistors (TFTs) have been fabricated using 400 nm polyimide (PI) cured at 250degC as gate dielectric. The root-mean square surface roughness of PI films is 30 Aring. An individual bottom gate, staggered structure was selected to study the device performance. The devices showed p-type electrical characteristics with field-effect mobility, threshold voltage and current on/off ratio values around 1.44 times 10-3 cm2V-1s-1, 1.1 V and 12, respectively.