Demonstration and characterization of an ambipolar high mobility transistor in an undoped GaAs/AlGaAs quantum well Appl. Phys. Lett. 102, 082105 (2013) Investigation of the charge transport mechanism and subgap density of states in p-type Cu2O thin-film transistors Appl. Phys. Lett. 102, 082103 (2013) Negative gate-bias temperature stability of N-doped InGaZnO active-layer thin-film transistors Appl. Phys. Lett. 102, 083505 (2013) A pH sensor with a double-gate silicon nanowire field-effect transistor Appl. Phys. Lett. 102, 083701 (2013) Extrinsic and intrinsic photoresponse in monodisperse carbon nanotube thin film transistors Appl. Phys. Lett. 102, 083104 (2013) Additional information on Appl. Phys. Lett.

Amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) having several metals, namely Ag, Ti, and Mo, as the source and drain electrodes were characterized. TFTs with Ti and Mo electrodes showed drain current–gate voltage characteristics without fluctuation. However, TFTs with Ag electrodes indicated a low noisy on-state current at a large channel length under a low drain–source voltage condition. The source and drain resistances [R s/d (Ω)] of the TFTs with each of the three metals were calculated from the I DS–V GS characteristics. The R s/d values of the Ag, Ti, and Mo samples reached 4 × 104, 2 × 104, and 1 × 104 Ω, respectively. This implies that a spatial potential barrier exists at the a-IGZO/Ag interface and that the resistance of the potential barrier changes with the application of gate voltage.

Amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors on glass substrates were fabricated, and the density of state (DOS) in TFTs after a negative bias stress (NBS) and negative bias illumination stress (NBIS) was investigated. For a NBIS of −20 V, the threshold voltage (V th ) shifted toward the negative direction but an increase of shallow states expected as positively ionized oxygen vacancies (V o + or V o ++ ) were not observed in the DOS curves. On the other hand, for NBIS of −30 V, changes in the DOS near the conduction band edge before and after applying a bias stress were observed. This suggests that V o + or V o ++ was generated by NBIS but accumulation of holes at the a-IGZO/SiO 2 interface mainly caused the V th shifts.Amorphous indium gallium zinc oxide (a-IGZO) is a transparent amorphous oxide semiconductor and is expected to be used as a channel material in thin film transistors (TFTs) for next-generation displays such as active matrix organic light-emitting diode displays. 1 Due to the electronic structure, a-IGZO TFTs have high electron fieldeffect mobility in spite of the material being amorphous. Moreover, it is easy to control the increase of the superfluous carrier density in a-IGZO TFTs compared to the case for TFTs fabricated from ZnO, which is a similar oxide semiconductor. 2 Moreover, very low off-state current is realizable because holes hardly exist. 3 Although a-Si is deposited by plasma enhanced chemical vapor deposition (PECVD) at approximately 350 • C, a-IGZO can be deposited by sputtering process at room temperature. Since a-IGZO TFTs are promising devices for low-temperature process, the application of a-IGZO TFTs to flexible electronics using a plastic substrate is expected. 4 In addition, TFTs with transparency in the visible wavelength are producible because of the wide bandgap. 5,6 The electrical stability of a-IGZO-TFTs under a positive bias stress (PBS) and a negative bias stress (NBS) has been reported by various researchers for practical applications. 7-14 In recent years, the negative shift of the threshold voltage (V th ) under negative bias illumination stress (NBIS) has been under focus. [15][16][17][18] Since TFTs are continually exposed to light irradiation in displays, for example backlight irradiation in liquid crystal displays, their reliability under illumination is a critical problem. Recently, some groups have reported that positively ionized oxygen vacancies (V olayers increased under NBIS, and these vacancies caused a negative shift in V th . 19 V o ++ and V o + are known as conventional defects in ZnO, a material similar to a-IGZO. 20,21 It has been proposed that V o ++ and V o + in a-IGZO exist shallow levels below the conduction band minimum and are derived from high concentration of natural vacancies (V o , 10 21 cm −3 , Ref. 22) that produce defect states near the valence band maximum.On the other hand, other groups have suggested diffusion of photoexcited holes to the SiO 2 /a-IGZO interface as the reason for the negative V th shift. 23 In addition, anothe...

Local heat produced by an electrical path inside the memory was detected and imaged by the method “Thermal Analysis.” It turned out that the visualized heat spots were conductive filaments (CFs) formed between interlayers of Pt/amorphous InGaZnO (a-IGZO). By using the thermal analysis, the location of CFs and their surface temperature was detected. This method indicated that there was a lot of emitted heat when the memory cell was switched off. It is thought to be accumulated heat causing disruption of the CFs. With great range of measurement, it was found that some memory cells drive with a single CF and others drive with multiple CFs. For the formation of CFs, it is assumed that there are CFs formation sites such as oxygen-related defects, roughness of the layer of a-IGZO, and so on. This method “Thermal analysis” can contribute to detection of the CF's location, the number of CFs, and thermal activity inside the memory devices.

The electronic structures of amorphous indium gallium zinc oxide (a-IGZO) on a SiO2 layers before and after annealing were observed by constant final state X-ray photoelectron spectroscopy (CFS-XPS) and X-ray adsorption near-edge structure spectroscopy (XANES). From the results of angle-resolved CFS-XPS, the change in the electronic state was clearly observed in the a-IGZO bulk rather than in the a-IGZO/SiO2 interface. This suggests that the electronic structures of the a-IGZO bulk strongly affected the thin-film transistor characteristics. The results of XANES indicated an increase in the number of tail states upon atmospheric annealing (AT). We consider that the increase in the number of tail states decreased the channel mobility of AT samples.