Electric field-enhanced metal-induced lateral crystallization and P-channel poly-Si TFTs fabricated by it

The poly-Si thin film was obtained by electric field-enhanced metal-induced lateral crystallization technique at low temperature. Raman spectra, X-ray diffraction (XRD) and scan electron microscope (SEM) were used to analyze the crystallization state, crystal structure and surface morphology of the poly-Si thin film. Results show that the poly-Si has good crystallinity, and the electric field has the effect of enhancing the crystallization when DC electric voltage is added to the film during annealing. Secondary ion mass spectroscopy (SIMS) shows that the metal Ni improves the crystallization by diffusing into the a-Si thin film, so the crystallization of the lateral diffused region of Ni is the best. The p-channel poly-Si thin film transistors (TFTs) were fabricated by this large-size grain technique. The I_DS−V_DS and the transfer characteristics of the TFTs were measured, from which, the hole mobility of TFTs was 65 cm²/V s, the on and off current ratio was 5×10⁶. It is a promising method to fabricate high-performance poly-Si TFTs at low temperature for applications in AMLCD and AMOLED.     

A study on the leakage current of poly-Si TFTs fabricated by metal induced lateral crystallization

Leakage current of poly-Si TFT fabricated by a metal induced lateral crystallization(MILC) process was investigated in terms of metal contamination and crystallization mechanisms. MILC poly-Si TFTs showed a higher leakage current than those by the solid phase crystallization method at high drain voltages. It turned out that the Ni rich phases in the depleted junction region played the role of trapping and recombination centers to generate the leakage currents and that the leakage current was generated by thermionic field emission. The leakage current could be drastically reduced to 5 pA/μm at V_GS=0 V and V_DS=15 V after the exclusion of the Ni-rich phase from the junction region by a Ni offset MILC process.     

Thermally generated leakage current mechanisms of metal-induced laterally crystallized n-type poly-Si TFTs under hot-carrier stress

Mechanisms of thermally generated leakage current have been systematically studied for metal-induced laterally crystallized n-type polycrystalline silicon thin film transistors under the hot-carrier stress. Various mechanisms of thermally generated leakage current are identified by both forward and reverse modes. The decrease of thermally generated leakage current is attributed to the depletion region modulation effect, which results from its shrinkage. While the increase of thermally generated leakage current is caused by the increase of the donor trap density, its increment relative to the initial one follows the Schottky model in the forward mode. Overall, the depletion region modulation effect dominates and the thermally generated leakage current decreases.     

The metal-induced crystallization of poly-Si and the mobility enhancement of thin film transistors fabricated on a glass substrate

In this study, we report on the fabrication of poly-crystalline silicon (poly-Si) using the metal-induced crystallization (MIC) method and its application to thin film transistors (TFTs). The top gate of the p-type TFTs, whose active layer used MIC poly-Si annealed for 1 h at 650 °C, showed a field effect mobility (μ_FE) of 7.5 cm²/V s. By increasing the crystallization time to 5 h, the quality of the MIC poly-Si was improved. The μ_FE increased from 7.5 to 15 cm²/V s. In order to enhance the channel mobility, the Si dangling bonds, which were produced during the transformation from the amorphous phase to the poly-crystalline phase of silicon (Si), were reduced by using plasma hydrogenation. Measurements show that the μ_FE reached 45 cm²/V s after passivation by an inductively coupled plasma chemical vapor deposition (ICPCVD) system.     

Extraction of trap densities in entire bandgap of poly-Si thin-film transistors fabricated by solid-phase crystallization and dependence on process conditions of post annealing

Trap densities (D_t) in entire bandgaps of poly-Si thin-film transistors (TFTs) fabricated by solid-phase crystallization (SPC) have been extracted by measuring low-frequency capacitance-voltage characteristics and using an extraction algorithm. The extraction algorithm is explained in detail. D_t in the upper and lower halves of the bandgap is extracted from n- and p-type TFTs, respectively. It is found that D_t is very roughly 10¹⁸ cm⁻³ eV⁻¹ near the midgap and becomes tail states near the conduction and valence bands. As a result, D_t is distributed like U shape in the bandgap, but humps appear around the midgap. Moreover, the dependence of D_t on process conditions of post annealing has been evaluated. It is found that the hump can be reduced by increasing annealing temperature and time because crystal defects generated during the SPC are extinguished during the post annealing.     

Device characteristics of amorphous indium gallium zinc oxide thin film transistors with ammonia incorporation

The effect of ammonia gas on amorphous indium gallium zinc oxide thin film transistors is investigated. The ammonia is incorporated into the sputtered a-IGZO film during the deposition process. The results indicate that the sub-threshold swing of the NH₃ incorporated TFTs is significantly improved from 2.8 to 1.0 V/decade, and the hysteresis phenomenon is also suppressed during the forward and reverse sweeping measurement. By X-ray photoelectron spectroscopy analyses, Zn-N and O-H bonds are observed in ammonia incorporated a-IGZO film. Therefore, the improvements in the electrical performance of TFTs are attributed to the passivation of dangling bonds and/or defects by ammonia.     

MoO3修饰氧化石墨烯作为空穴注入层影响研究

研究了MoO₃修饰氧化石墨烯(GO)作为空穴注入层的影响。采用旋涂的方法制备了GO, 再真空蒸镀修饰层MoO₃,得到了空穴注入能力强和透过率高的复合薄膜。MoO₃的厚分 别采用0、3、5和8nm。通过优化MoO₃的厚度发现,当MoO₃的厚为5nm时,复合薄膜 的透过率达到最大值,在 550nm的光波长下透光率为88%,且此时采用 复合薄膜作为空穴注入层制备的结构为 ITO/GO/MoO₃(5nm)/NPB(40nm)/Alq₃(40nm)/LiF(1nm)/Al(100nm)的有机电致发光器件(OLED)性能 最佳。通过对OLED进一步的优化,改变Alq₃的厚度,分别取50、60和70nm,测量其电压 、电流、亮度、色坐标和电致发光(EL)光谱等参数发现,当Alq₃的厚为50nm时器件性能最 佳。最终制备了结构为ITO/GO/MoO₃(5nm)/NPB(50nm)/Alq₃(50nm)/LiF(1nm)/Al(100 nm)的OLED,在电压为10V时,最大电流效率达到5.87cd/A,与GO单独作为空穴注入层制备的器件相比,提高了50%。