Myoung-Bok Lee

Applicability of ALE TiN films as Cu/Si diffusion barriers

Abstract Amorphous TiN films were deposited on a p-(100) Si substrate using an atomic layer epitaxy technique that employed TEMAT and NH 3 as precursors at a temperature range between 150 and 220°C. The average deposition rate was approximately 4.5 A/cycle and was in good agreement with the result expected from the layer-by-layer growth mode. The deposited TiN films showed excellent step coverage and uniformity for the trench with a high aspect ratio of h / w — 2.6:0.43 μm. The diffusion-barrier behavior of both as-deposited and post-annealed 45-nm thick TiN films at temperatures between 550 and 700°C were investigated against vacuum-evaporated Cu films using sheet resistance measurements, X-ray reflected diffraction, Auger electron spectroscopy, and scanning electron microscopy. The post-annealing of the ALE TiN films in a vacuum chamber of 2×10 −6 Torr was not found to be a very sensitive parameter for improving the diffusion-barrier function against Cu and Si; TiN films annealed up to 600°C for 1 h maintained the initial composition of both Cu/TiN and TiN/Si interfaces, thereby indicating a negligible interdiffusion of the Cu and/or Si species through the TiN film. However, a further increase of temperature above 650°C triggered Si and/or Cu interdiffusion resulting in a probable composition of Cu 3 Si.

A normally off GaN n-MOSFET with Schottky-barrier source and drain on a Si-auto-doped p-GaN/Si

We have fabricated an enhancement-mode n-channel Schottky-barrier-MOSFET (SB-MOSFET) for the first time on a high mobility p-type GaN film grown on silicon substrate. The metal contacts were formed by depositing Al for source/drain contact and Au for gate contact, respectively. Fabricated SB-MOSFET exhibited a threshold voltage of 1.65 V, and a maximum transconductance(g/sub m/) of 1.6 mS/mm at V/sub DS/=5V, which belongs to one of the highest value in GaN MOSFET. The maximum drain current was higher than 3 mA/mm and the off-state drain current was as low as 3 nA/mm.

Gas sensing characteristics of SnO2 thin film fabricated by thermal oxidation of a Sn/Pt double layer

SnO2 thin film with homogeneously dispersed nano-crystallite Pt particles was reliably prepared via simple thermal oxidation of a Sn/Pt double layer on Si substrate oxidized. Its surface phase and morphology were probed using some surface sensitive tools such as X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The electrical response of SnO2 thin films to the i-C4H10 gas was systematically investigated at a wide range of temperatures and gas concentrations. In particular, a long-term stability test of the fabricated Pt/SnO2 thin films for the i-C4H10 gas proved its applicability as a reliable gas sensor because of its higher sensing stability than the conventional Pt/SnO2 films over a long period of run time.

Growth of Semi-insulating GaN Layer by Controlling Size of Nucleation Sites for SAW Device Applications

Semi-insulating undoped GaN films were grown based on controlling the size of the nucleation sites through a special two-step growth method: First, 16 nm LT-GaN was annealed at 950 ° with a ramping time of 4 min, then the GaN was grown at this temperature for 1 min. Second, the growth temperature was increased to 1020° with a ramping time of 2 min and the GaN layer finally grown at 1020 ° for 40 min. The film grown by this sequence exhibited sheet resistance of up to 10 9 Ω/sq with mirror-like surface morphology. By slow ramping to 950° in the initial phase of growth, smaller grain sizes and higher nuclei densities were formed and the columnar growth mode along the c direction was dominant. The observation of higher resistance in two-step growth is believed due to the increased misorientation of nuclei when the growth proceeds during temperature ramping to 1020°. The fabricated saw filter on semi-insulating GaN exhibited a high velocity of 5342 m/s at center frequencies of 133.57 MHz and an electromechanical coupling coefficient( k 2 ) of about 0.763 %, which was enhanced due to the improvement of surface morphology with high sheet resistance by the two- step ramping technique.

Pt/AlGaN Metal Semiconductor Ultra-Violet Photodiodes on Crack-Free AlGaN Layers

Schotty-type solar-blind ultra-violet photodetectors were designed and fabricated by employing an unintentionally doped AlGaN layer, grown on a sapphire substrate by metal-organic chemical vapor deposition (MOCVD). When a low-temperature grown AlGaN interlayer was inserted between the GaN and AlGaN active layers, it was found to play an important role in decreasing the thermal and lattice mismatch-induced crack density in the active AlGaN layer. The Schottky-type photodetectors fabricated on the crack-free AlGaN layer then exhibited excellent electrical characteristics and UV sensing behavior. Accordingly, the resulting Pt/AlGaN metal semiconductor photodiode had a dark current of 9 nA at -5 V, cut-off wavelength of 310 nm, and quantum efficiency of 65% at 280 nm, plus the UV/visible extinction ratio was ~104 in the band edge, which is one of the highest values recorded for an AlGaN photodetector.

Field activated lateral-type polysilicon emitter with extremely high emission current and very low turn-on voltage

A lateral-type poly-Si field emission device was fabricated by utilizing the local oxidation of silicon (LOCOS) process and a simple and efficient activation technique of the tip end was proposed to achieve a high emission current. The fabricated single field emitter exhibits excellent electrical characteristics such as a very low turn-on voltage of 2 V and an extremely high current of ∼500 μA at anode to cathode voltage of 30 V. These superior field emission characteristics are believed to be due to both an increased enhancement factor (β) by appropriate activation and originally sharpened tip by the LOCOS process.

Fabrication and characteristics of lateral type GaN field-emission arrays using metalorganic chemical vapor deposition

Lateral type GaN field-emission diodes were fabricated by metalorganic chemical vapor deposition. In forming the pattern, two kinds of procedures were proposed: a selective etching method with electron cyclotron resonance-reactive ion etching (ECR-RIE) or a simple selective growth utilizing Si3N4 film as the masking layer. The device fabricated using ECR-RIE exhibited electrical characteristics such as a turn-on voltage of 35 V for a 7 μm gap and an emission current of ∼580 nA/10 tips at an anode-to-cathode voltage of 100 V. The field emission characteristics of GaN tips were attributed to the tip structure, low electron affinity and short distance between the cathode and anode tips.

Superior Characteristics of RuO2/GaN Schottky‐Type UV Photodetector

A RuO 2 /GaN Schottky diode was designed and fabricated for application as a UV photodetector. The fabricated RuO 2 /GaN Schottky diode showed a breakdown at over -50 V, plus a leakage current of 9 nA/cm 2 at -5 V with a good uniformity that was one order of magnitude lower than that of a Pt/GaN Schottky diode under the same epitaxial conditions. The proposed RuO 2 /GaN Schottky photodiode also exhibited a UV-visible rejection ratio of 3 × 10 and responsivity of 0.23 A/W at 330 nm.

Lateral field emitter arrays with high emission currents and wide operation region by high field activation

A lateral-type polysilicon field emission triode, consisting of two symmetric gate tips aligned by a 70° angle with respect to sharp cathode tips, was fabricated by using the local oxidation of polysilicon process. The fabricated device exhibited a low turn-on voltage of 13 V and an emission anode current of 3.6 μA/tip at VAC=50 V and VGC=open. After high field activation treatment, the turn-on voltage was reduced to 2 V and the emission anode current was increased to 9 μA/tip at the same bias condition. With changing gate bias, the emission current showed three different I–V characteristics; a negative resistance region with large transconductance of 200 μS/50 triodes, a positive resistance region with relatively small transconductance, and a zero transconductance region.

Emission behavior of nm-thick Al2O3 film-based planar cold cathodes for electronic cooling

We have fabricated and investigated the emission characteristics of planar cold cathodes which are appropriate for the electronic cooling devices by atomically depositing ultrathin Al2O3 films onto the indium-tin-oxide-coated glass. A diode-type test indicated prominent emission behaviors, such as a low threshold field of 3–5V∕μm for planar cold cathodes and the nonuniform luminescence intensity with localized distribution of emission spots. We propose a resonant Fowler–Nordheim tunneling of electrons transported via the Frenkel traps with a well depth of ϕB=0.8–0.9eV in nm-thick Al2O3 films as a key process for the extraordinary emission properties of Al2O3 film-based planar cold cathodes.