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The self-consistent technique for extracting density of states [DOS: g(E)] in an amorphous indium gallium zinc oxide (a-IGZO) thin film transistor is proposed and demonstrated. The key parameters are the g(E) of the a-IGZO active layer and the intrinsic channel mobility (μch). While the energy level (E) is scanned by the photon energy and gate-to-source voltage (VGS) sweep, its density is extracted from an optical response of capacitance-voltage characteristics. Using the Vos-dependent μch as another boundary condition, a linearly mapped DOS assuming a linear relation between VGS and E is translated into a final DOS by fully considering a nonlinear relation between VGS and E. The final DOS is finally extracted and verified by finding the self-consistent solution satisfying both the linearly mapped DOS and the measured VGS dependence of μch with the numerical iteration of a DOS-based μch model. The extracted final DOS parameters are NTA = 1.73 x 1017 cm-3 eV-1, NDA = 3.5 x 1015 cm-3 eV-1, kTTA = 0.023 eV, kTDGA = 1.2 eV, and EO = 1.7 eV with the formula of exponential tail states and Gaussian deep states. [ABSTRACT FROM AUTHOR]

A technique for extracting the acceptorlike density of states (DOS) of n-channel amorphous GaInZnO (a-GIZO) thin-film transistors based on the combination of subbandgap op- tical charge pumping and C-V characteristics is proposed. While the energy level is scanned by the photon energy and the gate voltage sweep, its density is extracted from the optical response of C-V characteristics. The extracted DOS shows the superpo- sition of the exponential tail states and the Gaussian deep states (NTA = 2 x 1018 eV' . cm3, NDA = 4 x iO'5 eV' . cm3, kTTA = 0.085 eV, kTDA = 0.5 eV, E0 = 1 eV). The TCAD simulation results incorporated by the extracted DOS show good agreements with the measured transfer and output characteris- tics of a-GIZO thin-film transistors with a single set of process- controlled parameters. [ABSTRACT FROM AUTHOR]

Currently, both high-density 3-D stacking nonvolatile (NV) memory and embedded NV memory in advanced systems on panel (SOPs) urgently demand the assistance of new and functional transition metal—oxide materials. This is to overcome serious fabrication issues encountered in the use of conventional Si or poly-crystalline Si materials, as well as to increase storage density with lower process cost. This paper reports the fully functional NV memory structure operated by an ionic amorphous oxide semiconductor with a wide energy band gap (> 3.0 eV) in a Ga2O3-In2O3-ZnO (GIZO) system under low process temperature (< 400 °C) while being combined with various metal-oxide materials of Al2O3, GIZO, and Al2O3 as the electron charge's tunneling, storage, and blocking layers, respectively. The different methods of memory programs and, especially, the unique erase characteristics caused by a much wider band gap than Si were intensively being investigated, and as a result, excellent electrical results of a large program/erase window over 3.8 V at a pulse time of 10 ms are achieved. [ABSTRACT FROM AUTHOR]

Amorphous Gallium-Indium-Zinc-Oxide (GIZO) thin film transistors with short channels of 50 nm were successfully fabricated by e-beam lithographic patterning. The GIZO thin film transistors showed a high mobility of 8.2 cm2/V · s with on-to-off current ratios up to 108. Excellent short channel characteristics were also obtained with a small shift of the threshold voltages and no degradation of subthreshold slopes as VDS increased, even with short channel lengths of less than 100 nm. These promising results indicate that the GIZO thin film transistors could be a candidate for selection transistors in 3-D cross point stacking memory. [ABSTRACT FROM AUTHOR]

Short channel device performance of deep-submicron gate length oxide thin film transistor (TFT) with amorphous InGaZnO (a-IGZO) active semiconductor is presented. Remarkable electrical properties of short channel oxide TFT were achieved utilizing crucial structure and material optimization such as self aligned gate structure with homo junction, multi-channel with rounded corners, and high-κ gate dielectric. It was found that various device performance parameters of short channel-oxide TFTs were significantly influenced by materials, processes, and structural geometry, which should be more carefully designed. [ABSTRACT FROM AUTHOR]

An extraction technique for subgap density of states (DOS) in an n-channel amorphous InGaZnO thin-film transistor (TFT) by using multifrequency capacitance-voltage (C-V ) characteristics is proposed and verified by comparing the measured I-V characteristics with the technology computeraided design simulation results incorporating the extracted DOS as parameters. It takes on the superposition of exponential tail states and exponential deep states with characteristic parameters for NTA=1.1×1017 cm-3 ·eV-1, NDA=4×1015 cm-3 ·eV-1, kTTA=0.09 eV, and kTDA=0.4 eV. The proposed technique allows obtaining the frequency-independent C-V curve, which is very useful for oxide semiconductor TFT modeling and characterization, and considers the nonlinear relation between the energy level of DOS and the gate voltage VGS. In addition, it is a simple, fast, and accurate extraction method for DOS in amorphous InGaZnO TFTs without optical illumination, temperature dependence, and numerical iteration. [ABSTRACT FROM AUTHOR]

The density of states (DOS)-based DC I-V model of an amorphous gallium-indium-zinc oxide (a-GIZO) thinfilm transistor (TFT) is proposed and demonstrated with selfconsistent methodologies for extracting parameters. By combining the optical charge-pumping technique and the nonlinear relation between the surface potential (4g) and gate voltage (VGS), it is verified that the proposed DC model reproduces well both the measured VGS-dependent mobility and the IDS-VGS characteristics. Finally, the extracted DOS parameters are NTA = 4.4 x 1017 cm-3 ∙ eV-1, NDA = 3 x 1015 cm-3∙eV-1, kTTA = 0.023 eV, kTDGA = 1.5 eV, and Eo = 1.8 eV, with the formulas of exponential tail states and Gaussian deep states. [ABSTRACT FROM AUTHOR]

Bipolar ac stress-induced instability of amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors is comparatively investigated with that under a positive dc gate bias stress. While the positive dc gate bias stress-induced threshold voltage shift (ΔVT) is caused by the charge trapping into the interface/gate dielectric as reported in previous works, the dominant mechanism of the ac stress-induced ΔVT is observed to be due to the increase in the acceptorlike deep states of the density of states (DOS) in the a-IGZO active layer. Furthermore, it is found that the variation of deep states in the DOS makes a parallel shift in the IDS-VGS curve with an insignificant change in the subthreshold slope, as well as the deformation of the CG-VG curves. [ABSTRACT FROM AUTHOR]

Abstract-The source/drain region of amorphous GaInZnO thin-film transistor with self-aligned top-gate structure was defined by simple NH[sub3] plasma treatment instead of complicated processes, such as ion implantation and activation. When the source/drain region of active layer was exposed to NH[sub3] gas plasma, the series resistance of the transistor decreased considerably. It exhibited electrical properties, such as a field-effect mobility of 6 cm[sup2]/V s, a threshold voltage of 0.21 V, and a subthreshold swing of 0.23 V/dec. [ABSTRACT FROM AUTHOR]

A fully transparent nonvolatile memory with the conventional sandwich gate insulator structure was demonstrated. Wide band gap amorphous GaInZnO (a-GIZO) thin films were employed as both the charge trap layer and the transistor channel layer. An excellent program window of 3.5 V with a stressing time of 100 ms was achieved through the well-known Fowler–Nordheim tunneling method. Due to the similar energy levels extracted from the experimental data, the asymmetrical program/erase characteristics are believed to be the result of the strong trapping of the injected negative charges in the shallow donor levels of the GIZO film. [ABSTRACT FROM AUTHOR]

We fabricated gallium-indium-zinc oxide (GIZO) thin film transistors (TFTs) having a double-gated (DG) structure and studied the back gate effect on device performance. DG GIZO TFTs showed better threshold voltage (Vth), swing factor (S), and on/off current than those with a single gate. With the variation in back gate bias, the device performance significantly changes due to the modification of field distribution near the GIZO channel. It is believed that our DG structure is an effective way to improve the performance of GIZO oxide transistors and suppress the formation of an accumulation layer at the back surface. [ABSTRACT FROM AUTHOR]

We have demonstrated a self-aligned top-gate amorphous gallium indium zinc oxide thin film transistor (a-GIZO TFT). It had a field effect mobility of 5 cm2/V s, a threshold voltage of 0.2 V, and a subthreshold swing of 0.2 V/decade. Ar plasma was treated on the source/drain region of the a-GIZO active layer to reduce the series resistance. After Ar plasma treatment, the surface of the source/drain region was divided into In-rich and In-deficient regions. The a-GIZO TFT also had a constant sheet resistance of 1 kΩ/□ for a film thickness of over 40 nm. The interface between the source/drain Mo metal and the Ar plasma-treated a-GIZO indicated a good Ohmic contact and a contact resistivity of 50 μΩ cm2. [ABSTRACT FROM AUTHOR]

Amorphous-gallium-indium-zinc-oxide (a-GIZO) thin filmtransistors (TFTs) are fabricated without annealing, using processes and equipment for conventional a-Si:H TFTs. It has been very difficult to obtain sound TFT characteristics, because the a-GIZO active layer becomes conductive after dry etching the Mo source/drain electrode and depositing the a-SiO2 passivation layer. To prevent such damages, N2O plasma is applied to the back surface of the a-GIZO channel layer before a-SiO2 deposition. N2O plasma-treated a-GIZO TFTs exhibit excellent electrical properties: a field effect mobility of 37 cm2/V s, a threshold voltage of 0.1 V, a subthreshold swing of 0.25 V/decade, and an Ion/off ratio of 7. [ABSTRACT FROM AUTHOR]

In this letter, we investigated the effects of source/drain series resistance on amorphous gallium-indium-doped zinc-oxide (a-GIZO) thin film transistors (TFTs). A linear least square fit of a plot of the reciprocal of channel resistance versus gate voltage yields a threshold voltage of 3.5 V and a field-effect mobility of about 13.5 cm² / V · s. Furthermore, in a-GIZO TFTs, most of the current flows in the distance range of 0-0.5 µm from the channel edge and shorter than that in a-Si:H TFTs. Moreover, unlike a-Si:H TFTs, a-GIZO TFTs did not show an intersection point, because they did not contain a highly doped ohmic (n+) layer below the source/drain electrodes. [ABSTRACT FROM AUTHOR]