Jun Hyuk Cheon

Active-matrix OLED on bendable metal foil

This brief reports a flexible active-matrix organic light-emitting diode display based on a poly-Si thin-film transistor (TFT) backplane. The p-channel poly-Si TFTs on metal foil exhibited a maximum field-effect mobility of 86.1 cm/sup 2//Vs, threshold voltage of 3.5 V, gate voltage swing of 0.8 V/dec, and the minimum off current of 10/sup -12/ A//spl mu/m at V/sub ds/=-0.1 V. A 4.1-in active-matrix backplane was fabricated with the poly-Si TFT with a conventional pixel circuit consisting of 2 TFTs and one capacitor. The scan driver circuits with PMOS were integrated on the flexible metal foil. The top emission, organic light emitting display having a brightness of 100 cd/m/sup 2/.

54.4: 4.1 inch Top-Emission AMOLED on Flexible Metal Foil

We have developed a 4.1 inch AMOLED display with top emission structure on stainless steel foil. The p-channel TFTs on metal foil exhibited the field-effect mobility of 75.1 cm2/Vs, threshold voltage of −3.9V, and subthreshold swing of 0.9V/dec. Active-matrix back planes were fabricated with the poly-Si TFT with a conventional pixel circuit consisting of 2 TFTs and 1 cap. The scan driver circuits with PMOS were integrated on the metal foil.

Ultrathin Si Thin-Film Transistor on Glass

We have studied the fabrication of ultrathin single-crystalline-silicon thin-film transistors (TFTs) on glass. The single-crystalline Si layer was transferred to glass by hydrogen implantation and anodic bonding. The thickness of the silicon-on-glass (SiOG) was controlled down to 10 nm by dry etching. The p-channel SiOG TFTs with 10-nm-thick Si exhibited the field-effect mobility of 134.9 cm2/Vmiddots, threshold voltage of -1.5 V, and gate voltage swing of 0.13 V/dec. The TFTs were found to be stable against gate bias stress of +30 or -30 V.

Inverted Staggered Poly-Si Thin-Film Transistor With Planarized SOG Gate Insulator

In this letter, we have studied the inverted staggered thin-film transistor (TFT) using a spin-on-glass (SOG) gate insulator and a low-temperature polycrystalline silicon (poly-Si) by Ni-mediated crystallization of amorphous silicon. The p-channel poly-Si TFT exhibited a field-effect mobility of 48.2 cm2/V ldr s, a threshold voltage of -4.2 V, a gate-voltage swing of 1.2 V/dec, and a minimum off-current of < 4 times 10-13A/ mum at Vds = -0.1 V. Therefore, the gate planarization technology by SOG can be applicable to low-cost large-area poly-Si active-matrix displays.

Anomalous Increase of Grain Size in Ni-Mediated Crystallization of Amorphous Silicon

We studied the grain growth in Ni-mediated crystallization of amorphous silicon (a-Si) films with various thicknesses. The Ni particles with density of 3.39 X 10 1 3 cm - 2 was deposited on a-Si and this was annealed at 580°C for 15 min. The grain size of the crystallized poly-Si increases from 25 to 104 μm as the thickness of a-Si increases from 20 to 300 nm. The grain size has a linear relationship with the a-Si thickness. This can be understood on the basis of the cylindrical seed formation and subsequent cylindrical, lateral grain growth. A cylindrical grain was found in atomic force microscope image of a partially crystallized a-Si after the Secco etch of surrounding a-Si phase.

Coplanar Poly-Si TFT on Flexible Metal Foil Using Spin-On Glass as Gate Insulator and Planarization

Methylsiloxane-based spin-on-glass (M-SOG) has been applied to a polycrystalline silicon thin-film transistor (TFT) on a 40 μm-thick flexible metal foil as a gate dielectric and planarization layer as well. Triple spin coatings and curing of M-SOG layers reduce the surface roughness of the metal foil from 800 to 56 A. The p-channel metal-induced crystallization of a-Si using a cap TFT using M-SOG on a metal foil exhibited a field-effect mobility of 51.1 cm 2 /V s, a threshold voltage of -4.3 V, and a minimum off-state current of <1.74 X 10 -12 A/μm at V ds = -0.1 V. The poly-Si TFT was found to be stable against a negative gate-bias stress. Therefore, the low-cost, low-temperature polycrystalline silicon TFT can be applied to make flexible displays.

30.3: Highly Flexible Low Power Consumption AMOLED Displays on Ultra-Thin Stainless Steel Substrates

We present results demonstrating that low power consumption phosphorescent AMOLED displays can be fabricated on ultra-thin (25 μm) stainless steel substrates, combining an amorphous silicon backplane with a top emission phosphorescent OLED frontplane. Preliminary results show the performance of amorphous silicon backplanes adequate to drive AMOLED displays, and flexibility results on these backplanes show that they operate when conformed to a tight diameter of only 5 mm.

Location control of giant silicon grains using organic lenses

We studied the location control of a giant grain of polycrystalline silicon produced by Ni-mediated crystallization of amorphous silicon (a-Si) using a cap layer. An organic lens made of acryl was used for the focusing of light for the seed formation and subsequent crystallization. A single grain 62μm in diameter was made using an 80-μm-square SiNx cap layer on the a-Si. The position of a thin-film transistor (TFT) on a grain can be controlled, so that a single grain TFT can be fabricated at a predetermined position without use of the laser annealing technique.

Reduction of Off-State Currents in Silicon on Glass Thin Film Transistor by Off-State Bias Stress

We have studied the impact of off-bias stress on the performance of thin film transistors (TFTs) fabricated on single crystalline silicon-on-glass substrates. The p-channel TFT transfer characteristics typically exhibit excellent on-state performance with a field-effect mobility of 203 cm 2 /V s and a subthreshold swing of around 200 mV/dec. However, the off-state drain current has increased with increasing gate voltage. This increasing off-state current phenomenon can be significantly reduced by performing an off-state bias for 10 s. The formation of electron traps in the gate oxide near the drain is the main factor that reduces the off-state leakage current.

Effect of Oxygen-Plasma Treatment on Formation of LTPS on SOG by Metal-Mediated Crystallization

We have studied the oxygen-plasma effect on spin-on-glass (SOG) on the growth of low-temperature polycrystalline silicon (LTPS) by metal-mediated crystallization. The SOG buffer was coated on glass, and then it was exposed to oxygen plasma before the deposition of amorphous silicon (a-Si) to turn the SOG surface to hydrophilic. The a-Si on SOG was crystallized by metal-induced crystallization through a cap. The crystalline structure depended on the surface treatment: disk-shaped grains were grown on the O 2 -plasma-treated SOG, but needlelike grains were on the SOG without O 2 -plasma treatment. The p-channel poly-Si thin film transistor using the LTPS on O 2 -plasma-treated surface exhibited a field-effect mobility of 91.1 cm 2 /V s, a threshold voltage of -8.5 V, and a gate voltage swing of 1.2 V/dec.