Sungwook Jung

Fabrication and characterization of metal-oxide-nitride-oxynitride-polysilicon nonvolatile semiconductor memory device with silicon oxynitride (SiOxNy) as tunneling layer on glass

A nonvolatile semiconductor memory (NVSM) device with a metal-oxide-nitride-oxynitride-polysilicon (MONOS) structure on a rough polysilicon (poly-Si) surface was fabricated using a low-temperature process and poly-Si thin film transistor (TFT) technology on glass. For the fabrication of the NVSM device on glass, plasma-assisted oxynitridation was carried out using nitrous oxide (N2O) as a reactive gas, due to the very rough surface of the poly-Si on glass annealed using an excimer laser. The ultrathin SiOxNy films obtained using the N2O plasma have a very uniform distribution on poly-Si and similar contents of oxygen and nitrogen in the peaks and valleys of the grains. The NVSM devices having a MONOS structure with a tunneling layer of ultrathin SiOxNy on glass have suitable switching and charge retention characteristics for data storage. The results demonstrate that the NVSM device made using low-temperature poly-Si TFT technology on glass reported in this paper can be used in various types of display de...

SiO2 Films Deposited by APCVD with a TEOS/Ozone Mixture and Its Application to the Gate Dielectric of TFTs

Silicon dioxide (SiO 2 ) films were deposited using atmospheric pressure chemical vapor deposition (APCVD) with tetraethyl orthosilicate (TEOS) and ozone (O 3 ) as reactant gases. These films were used as the gate dielectric of low temperature polycrystalline silicon (LTPS) thin film transistors (TFTs). 0 3 gas was chosen instead of oxygen (0 2 ) gas because the latter is not compatible with the low temperature processing of LTPS TFTs. SiO 2 films deposited at low temperatures (<450°C) have low Si-OH contents and electrical properties desirable for gate insulator materials. Although the LTPS TFTs were fabricated using low cost SiO 2 films deposited by APCVD as the gate dielectric, the fabricated devices exhibited a field-effect mobility of 49 cm 2 /V s and a subthreshold swing of 490 mV/dec. The results demonstrate that SiO 2 deposited by APCVD with TEOS and 0 3 is a promising material for low cost and high quality gate insulators for LTPS TFTs.

Embedded LTPS flash cells with oxide–nitride–oxynitride stack structure for realization of multi-function mobile flat panel displays

In this paper, embedded flash (eFlash) cells were fabricated for realization of multi-functions, such as systems on panels (SOPs) and threshold voltage (VTH) stabilization of flat panel displays (FPDs). Fabrication was via low temperature polycrystalline silicon (LTPS) thin film transistor (TFT) technology and an oxide–nitride–oxynitride (ONOn) stack structure on glass. Poly-silicon (poly-Si) on glass, which was annealed via an excimer laser, has a very rough surface. To fabricate LTPS eFlash cells on glass with a very rough poly-Si surface, plasma-assisted oxynitridation was performed; nitrous oxide (N2O) served as a reactive gas. LTPS eFlash cells have excellent TFT electrical properties, such as VTH, a high On/Off current ratio and a low sub-threshold swing (S). The results demonstrate that eFlash cells fabricated on glass with a rough silicon surface, via an ONOn stack structure, have switching characteristics suitable for data storage, such as a low operating voltage (<±10 V) suitable for mobile FPDs, a threshold voltage window, ΔVTH, which exceeds 2.3 V, between the programming and erasing (P/E) states, over a period of 10 years, and the capacity to retain the initial ΔVTH over a period of 105 P/E operations.

High performance nonvolatile memory using SiO2/SiOx/SiOxNy stack on excimer laser-annealed polysilicon and the effect of blocking thickness on operation voltage

Silicon-rich SiOx material is a good charge storage candidate for memory applications that promise a large memory window and low operation voltage. Nonvolatile memory (NVM) devices fabricated on excimer laser-annealed polysilicon using SiO2/SiOx/SiOxNy (OOxOn) structure are investigated with SiO2 blocking thicknesses changing from 15 to 20 to 30 nm. The Si-rich SiOx material exposed numerous non-bridging oxygen hole-centre defect sources and a rich silicon phase in the base material. These defects, as well as amorphous silicon clusters existing in the SiOx layer, enhance the charge storage capacity of the device. Retention properties were ensured by 3.2 nm SiOxNy tunnelling layer growth via N2O plasma-assisted oxynitridation. NVM characteristics showed a retention exceeding 85% of the threshold voltage shift after 104 s and greater than 70% after 10 years. Depending on the blocking thickness of 15, 20 or 30 nm, operating voltages varied from ±9 to ±13 V at a programming/erasing duration of only 1 ms. These excellent operating properties of the OOxOn structure make it a potential competitor among the new generation of memory structures on glass.

Memory characteristics of poly-Si using MIC as an active layer on glass substrates

In this paper the electrical properties of nonvolatile memory (NVM) using multi-stack gate insulators of oxide–nitride–oxynitride (ONOn) and an active layer of low temperature polycrystalline silicon (LTPS) were investigated. From hydrogenated amorphous silicon (a-Si : H), the LTPS thin film with a high crystalline fraction of 96% and a low surface roughness of 1.28 nm was fabricated by metal induced crystallization (MIC) with annealing conditions of 650 °C for 5 h on glass substrates. The LTPS thin film transistor or the NVM had a field effect mobility of (μFE) 10 cm2 V−1 s−1 and a threshold voltage (VTH) of −3.5 V. The results demonstrated that the NVM had a memory window of 1.6 V with a programming and erasing (P/E) voltage of −14 V and 14 V in 1 ms. Moreover, retention properties of the memory were shown to exceed 80% after 10 years. Therefore, the LTPS fabricated by MIC has become a potential material for NVM application which is employed for the system integration of panel displays.

Nanocrystalline-Silicon Thin-Film Nonvolatile Memory Devices for Display Applications

Nanocrystalline-silicon (nc-Si) nonvolatile memory (NVM) devices with oxynitride-nitride-oxide stack structures were fabricated with directly deposited nanocrystalline-silicon thin films using a low-temperature process. The fabricated bottom-gate nc-Si NVM devices have a wide memory window with a low operating voltage during programming and erasing due to an effective control of the gate dielectrics. In addition, after ten years, the memory device retains a memory window of over 67% between the programming and erasing states. These results demonstrate that these low-priced nc-Si NVM devices have a suitable programming and erasing efficiency for data storage under low-voltage conditions, in combination with excellent charge retention characteristics.

Embedded NVM Devices with Solid-Phase Crystallized Poly-Si Film on a Glass Substrate for System-on-Panel Applications

Embedded nonvolatile memory (NVM) devices with solid-phase crystallized polycrystalline silicon (poly-Si) films and an oxide-nitride-oxynitride (ONOn) stack structure on a glass panel were fabricated and investigated for system-on-panel applications. Memory-in-pixel and memory blocks are expected to be integrated in display panels as the integration of display systems progresses. Poly-Si thin-film transistor technology and a low temperature method to deposit an ultrathin tunneling layer using plasma-assisted oxynitridation were used to fabricate embedded poly-Si NVM devices on glass panels. A memory window from +2.4 to - 1.72 V was obtained at a low operating voltage with an erasing voltage of +11 V and a programming voltage of - 10 V. Moreover, an extrapolation of the performance of the fabricated poly-Si NVM device suggests that it retains a threshold voltage window of more than 80% between the programming and erasing states up to 10 years. The results demonstrate that the proposed devices with poly-Si layers using solid-phase crystallization and ONOn stack structures have suitable switching and retention characteristics for data storage applicable to real flat-panel display applications.

Embedded nonvolatile memory devices with various silicon nitride energy band gaps on glass used for flat panel display applications

Nonvolatile memory (NVM) devices with a nitride–nitride–oxynitride stack structure on a rough poly-silicon (poly-Si) surface were fabricated using a low-temperature poly-Si (LTPS) thin film transistor technology on glass substrates for application of flat panel display (FPD). The plasma-assisted oxidation/nitridation method is used to form a uniform oxynitride with an ultrathin tunneling layer on a rough LTPS surface. The NVMs, using a Si-rich silicon nitride film as a charge-trapping layer, were proposed as one of the solutions for the improvement of device performance such as the program/erase speed, the memory window and the charge retention characteristics. To further improve the vertical scaling and charge retention characteristics of NVM devices, the high-κ high-density N-rich SiNx films are used as a blocking layer. The fabricated NVM devices have outstanding electrical properties, such as a low threshold voltage, a high ON/OFF current ratio, a low subthreshold swing, a low operating voltage of less than ±9 V and a large memory window of 3.7 V, which remained about 1.9 V over a period of 10 years. These characteristics are suitable for electrical switching and data storage with in FPD application.

Investigation of Aluminum Metallized Source/Drain Thin Film Transistors Using a Self-Aligned Fabrication Process

For a better thin film transistor performance, metal silicide has been studied in order to enhance the conductivity of the source and drain electrodes. Although aluminum does not form a metal silicide with silicon, the two materials interpenetrate in an induced crystallization process. In such a structure, aluminum can act as a p-type dopant in the silicon lattice. In this work, aluminum metallized source/drain thin film transistors with excimer laser-annealed polycrystalline silicon were fabricated using a simple self-aligned process. The source/drain regions were patterned with a lift-off process. The n-channel characteristics of the as-deposited aluminum source/drain were explored and an improvement in the performance was observed after a heat treatment at 250 °C for 1 h. The devices treated at 350 °C for 10 h exhibited p-channel characteristics. The device characteristics were compared with another fabricated p-type doped source/drain structure. A remarkable enhancement in the performance of the aluminum metallized source/drain devices was observed. These structures yielded a peak field effect mobility of about 105 cm2V-1s-1. The simple fabrication process and resulting enhancement in device performance makes this type of structure ideal for use in thin film transistors on glass.

Performance evaluation of coreless axial flux permanent magnet wind generator

Numerical design characteristics of coreless axial flux permanent magnet synchronous generator (AFPMSG) for wind turbine have been investigated in terms of output voltage and current, total harmonic distortion, efficiency, and inductance. The 3 .2 kW coreless AFPMSG is analyzed using 3D nonlinear finite element method.