Double Channel Layer Research Articles

Effects of Mg Doping on Double Channel Layer Atmospheric Pressure-Plasma Enhanced Chemical Vapor Deposition Fabricated Amorphous InGaZnO Thin Film Transistors

Amorphous IGZO (a-IGZO) has been proved to be a suitable material for the channel layer in a thin film transistor, showing high mobility even in low temperature fabrication, device electrical characteristic exceeds a-Si or other metal oxide semiconductor materials. In this work, bottom gate top TFT is fabricated. With Atmosphere Pressure-PECVD (AP-PECVD), a-IGZO is deposited as device channel layer. A double channel layer is tested with Mg doping added in the bottom layer. This work focus on how the Mg doping concentration in the bottom layer affects device electrical characteristic. The result for best device characteristics is 5% Mg doping, showing highest mobility, lowest threshold voltage, and nearly 108 in Ion/Ioff. A suitable doping concentration can lower interface defect density and affect grain size, which both leads to a better device characteristics. However, device characteristics show sign of degradation with excess doping concentration.

Enhanced electrical properties of oxide semiconductor thin-film transistors with high conductivity thin layer insertion for the channel region

This study examined the performance and the stability of indium tin zinc oxide (ITZO) thin film transistors (TFTs) by inserting an ultra-thin indium tin oxide (ITO) layer at the active/insulator interface. The electrical properties of the double channel device (ITO thickness of 5nm) were improved in comparison with the single channel ITZO or ITO devices. The TFT characteristics of the device with an ITO thickness of less than 5nm were degraded due to the formation of an island-like morphology and the carriers scattering at the active/insulator interface. The 5 nm-thick ITO inserted ITZO TFTs (optimal condition) exhibited a superior field effect mobility (∼95cm2/V·s) compared with the ITZO-only TFTs (∼34cm2/V·s). The best characteristics of the TFT devices with double channel layer are due to the lowest surface roughness (0.14nm) and contact angle (50.1°) that result in the highest hydrophicility, and the most effective adhesion at the surface. Furthermore, the threshold voltage shifts for the ITO/ITZO double layer device decreased to 0.80 and −2.39V compared with 6.10 and −6.79V (for the ITZO only device) under positive and negative bias stress, respectively. The falling rates of EA were 0.38eV/V and 0.54eV/V for the ITZO and ITO/ITZO bi-layer devices, respectively. The faster falling rate of the double channel devices suggests that the trap density, including interface trap and semiconductor bulk trap, can be decreased by the ion insertion of a very thin ITO film into the ITZO/SiO2 reference device. These results demonstrate that the double active layer TFT can potentially be applied to the flat panel display.

Influence of Double Channel Layers on the Performance of Nitrogen Doped Indium-zinc-oxide Thin Film Transistors

The nitrogen-doped amorphous indium-zinc-oxide thin film transistors with double channel layers (a-IZO/IZON-TFTs) were fabricated by RF magnetron sputtering of IZO target on the thermal oxidized p-type Si substrate. Influence of the double channel layers on the electrical performance and thermal stability of the devices were investigated. It is found that a-IZO/IZON-TFTs have high field effect mobility of 23.26 cm/(Vs) and more positively shifted threshold voltage than that of a-IZO-TFTs. This is ascribed to the doped nitrogen which can help reduce oxygen vacancy in the channel layer, suppress carrier concentration and make the devices have a better threshold voltage. Meanwhile, employing a-IZO thin film can avoid the sharp drop of field effect mobility and drain on current caused by nitrogen doping on a-IZON layer, leading to promoting Ion/Ioff ratio effectively. Besides, according to the transfer characteristics measured at temperatures from 298 K to 423 K, devices with a-IZO/IZON double layers have superior performance and thermal stability to TFTs of single channel layer, which can be ascribed to the protective effect of a-IZON thin film on the channel layers. The doped nitrogen can reduce the adsorption/desorption reaction of oxygen molecules on the back channel layer, leading to a significant improvement on thermal stability of the devices. 746 无 机 材 料 学 报 第 31卷

Low-voltage transparent thin-film transistors with ZnO/ITO double-channel layers

We report an investigation of the effects of thin film transistors (TFTs) using double-channel layers on the electrical properties of transparent ZnO TFTs. TFTs were fabricated at room temperature, which with ZnO channel layers exhibit a performance with an on/off ratio of 105, a subthreshold swing of 0.11 V/decade, and a mobility of 4.6 cm2 V−1 s−1. The field-effect mobility, current on/off ratio, and subthreshold swing of such TFTs with ZnO/ITO double-channel layers were estimated to be 21 cm2 V−1 s−1, 106, and 0.1 V/decade, respectively. The mobility, switching operation, and on/off ratio of the ZnO TFTs were improved considerably after ITO channel deposition.

A strategy for performance enhancement of HfInZnO thin film transistors using a double-active-layer structure

We investigate the electrical performance and negative bias stability of thin film transistors (TFTs) using double active layer. Double active layer is consisting of low oxygen content HfInZnO film as bottom channel and high oxygen content HfInZnO film as back channel. The HfInZnO-TFT with double channel layer shows a high mobility of 6.8cm2/Vs, a low threshold voltage of −0.3V, and a threshold voltage shifts of 0.65V under −20V gate bias for 7200s. The results suggest that HfInZnO with low oxygen content as the bottom channel could provide high carrier concentration and good HfInZnO/Al2O3 interface to improve field-effect mobility and negative bias stress stability. HfInZnO with high oxygen content as back channel can control the conductivity to reduce the off current of TFT. Thus, a double-active-layer structure is an effective way to improve the electrical performance of HfInZnO-TFT.

Spectrum Analysis of 2-D Plasmon in GaN-Based High Electron Mobility Transistors

We have investigated terahertz (THz) resonant absorption spectra in grating-gate GaN high electron mobility transistors. The results indicate that both the symmetrical plasmon mode and the asymmetrical plasmon mode play an important role in the strong absorption of THz waves. The excitation process and dynamic response of these plasmons are investigated in detail. Our results also indicate that the asymmetrical plasmon is induced by the surface polarization field of the electrodes and the resonant strength of this plasmon is reduced significantly by the decay of the polarization field. Variations in the resonant strength of the plasmonic peaks are consistent with the surface resonant layer model showing that the method we used can be utilized for the study of coupling between THz radiation and plasmons in the channel. In order to achieve wider tunability, more advanced device structures can be explored such as a device that contains double channel layers, in which complicated plasmons can be excited.

Electrical properties of top-gate oxide thin-film transistors with double-channel layers

Using ZnO, and three compositional In 2O 3-Ga 2O 3-ZnO (IGZO, In:Ga:Zn=1:1:1, 2:1:2, 2:2:1, atomic ratio) semiconductors, we have made and evaluated several double layered oxide thin-film transistors (TFTs). The drain current was mainly affected by the nearer channel material to a gate insulator. From the positive bias stress (PBS) tests, however, the electrical stability showed a complicated result, depending on both channel structures and post-heat treatments.

Investigation of the effects of interface carrier concentration on ZnO thin film transistors fabricated by atomic layer deposition

Thin films of ZnO were deposited by atomic layer deposition (ALD) at different process temperatures and the resulting chemical and electrical characteristics were investigated. As the process temperature increased, the ZnO film exhibited an increase in carrier concentration from 1.3 × 1015 to 2.1 × 1019 cm−3, and a decrease in resistivity from 6.7 × 103 to 8.2 × 10−3 Ω cm. We utilized this temperature dependence of the electrical properties and fabricated thin film transistors (TFTs) at different temperatures with both single and double channel layers. In the ZnO-TFT with a single channel layer, the overall device performance of the ZnO-TFT, such as the Ion/Ioff ratio and subthreshold swing (SS), was degraded as the entire channel resistance decreased. In contrast, the ZnO-TFT with a double channel layer could control the turn-on voltage and threshold voltage by suppressing the increase in the off-current. The Ion/Ioff ratios were 8.6 × 105, 2.2 × 106 and 4.7 × 105 and the subthreshold swings exhibited 0.60 V/decade, 0.71 V/decade and 0.68 V/decade for the TFT with interface channel layers deposited at 120 °C, 140 °C and 160 °C, respectively. The saturation mobility slightly increased from 1.267 to 1.912 cm V−1s−1 as the process temperature of the interface channel layer increased.