Woon Choi

Direct observation of electron emission site on boron-doped polycrystalline diamond thin films using an ultra-high-vacuum scanning tunneling microscope

Surface morphology characteristics and electron emission properties of boron-doped polycrystalline diamond thin films grown by microwave plasma-assisted chemical-vapor deposition were investigated using an ultra-high-vacuum scanning tunneling microscope. Small secondary grains with average size less than 10 nm were observed to be on top of the isolated crystal surfaces. The current imaging tunneling spectroscopy (CITS) study revealed that high electron emission occurred at some crystalline facets while others showed relatively no measurable electron emission. The CITS study at high magnification also indicated that the electron emission was initiated at the grain boundaries rather than at the top of the grains. This observation suggests that the electrons transport through the grain-boundary conductive channels and preferentially emit at the low electron affinity facets.

Influence of uniaxial mechanical stress on the high frequency performance of metal-oxide-semiconductor field effect transistors on (100) Si wafer

The effects of uniaxial mechanical stress on the radio frequency performance of n- and p-metal-oxide-semiconductor field effect transistors (MOSFETs) are investigated up to 10 GHz. Under tensile stress, the gate transconductance (gm) increases in the n-MOSFETs while it decreases in the p-MOSFETs, whereas the results were vice versa for compressive stress. The total gate capacitance (CG) extracted from scattering parameters increases (decreases) under tensile (compressive) stress for both n- and p-MOSFETs, which is explained by the variation in the effective mass perpendicular to the Si/SiO2 interface. The cut-off frequency (fT) varies in inverse proportion to the CG variation.

AlGaAs/GaAs NpnP Depleted Optical Thyristor Using Bottom Mirror Layers

A novel fully depleted optical thyristor (DOT) using quarter wavelength reflector stacks (QWRS) is proposed. QWRS are employed as bottom mirrors to enhance the emission efficiency as well as optical sensitivity. To analyze their switching characteristics, s-shapes nonlinear current–voltage curves were simulated and the reverse full-depletion voltages (Vnegs) of DOTs were obtained as a function of semiconductor parameters using a finite difference method associated with a current-oriented method. The fabricated DOTs show sufficient nonlinear s-shaped current–voltage (I–V) characteristics, and switching voltage changes with and without bottom mirrors are 1.82 V and 1.52 V, respectively. Compared to a conventional DOT, this device with the bottom mirror shows about 20% and 20–50% enhancement in switching voltage changes and spontaneous emission efficiency, respectively.

Field-Emission Activation on Boron-Doped Chemical-Vapor-Deposited Polycrystalline Diamond Films

Spatial variation of field-emission currents in boron-doped polycrystalline diamond thin films grown by microwave plasma-assisted chemical-vapor deposition was investigated. Random distribution of electron emission sites was observed in microscale and the electron emission was inhomogeneous. Electron emission current was significantly increased for the higher boron-doping concentration and decreased in the thicker films. Activation of electron emission in the low electron emission area was observed. Threshold electric field was significantly decreased after a voltage-stressed activation process. These activated electron emission sites were stable and showed reproducible electron emission. The electron emission activation was possibly due to the diamond surface phase transformation and/or formation of conductive channels at the grain boundaries.

Evaluation of through-silicon-via process using scanning laser beam induced current (SLBIC) system

The manufacturing process of through-silicon-via (TSV) for 3D integration is complicated, and the high yield for each process is required. The relationship between the depth of the barrier/seed layer and the electroplating copper fill is investigated by using the scanning laser beam induced current (SLBIC) method. After reactive etching of via holes with diameters ranging from 50 μm to 150 μm, copper seed layer is deposited by sputtering, and then the electroplating of copper is performed. From the back surface of the sample, the infrared laser beam with wavelength of 1064nm was scanned, and the induced current between copper layer and silicon back surface is measured in order to obtain the current image. By changing the focus point of laser beam, the location of TSV failure is analyzed in depth direction.

Electron and laser beam-induced current measurements of diamond-like carbon films modified by scanning probe method

A nitrogen-doped diamond-like carbon (DLC) film deposited on n-type silicon is modified by applying an electric field in a vacuum between a tungsten tip and the DLC film surface using a scanning probe field emission current method. The resistance decreases and a Schottky barrier is formed between the modified DLC and the silicon surface, while micro-Raman measurements show a slight nano-crystalline graphitization. The electron beam induced current from the modified area is measured without any metal contact deposition. An infrared laser beam with a wavelength of 1400 nm is scanned across the backside of the silicon, and the induced current from the DLC modified area is measured. It is shown that both infrared laser and electron beam induced current measurements were possible for the modified DLC film on silicon structures.

Scanning laser induced current measurements on silicon wafer with through silicon via structure

The scanning laser beam induced current is measured on a silicon wafer with through silicon via (TSV) structure. The current image is obtained by changing the focused point of the infrared laser from the surface to the inside of silicon. The current contrast due to the defect of the insulating layer is obtained, and the defect point in the via hole is estimated from the brightness of the image versus distance from the surface.

Impacts of uniaxial mechanical stress on high frequency performance of MOSFETs

The effects of uniaxial mechanical stress on the radio frequency (RF) performance of n- and p-metal-oxide-semiconductor field effect transistors (MOSFETs) fabricated on (100) Si wafer are investigated up to 10 GHz. Uniaxial mechanical stress is applied to the MOSFETs parallel to the direction of drain current flow using a four-point bending fixture. Under tensile stress, the gate transconductance (gm) increases in the n-MOSFETs while it decreases in the p-MOSFETs, whereas the results were vice versa for compressive stress. These tendencies are same to the effects of uniaxial mechanical stress on direct current (DC) transconductance of the MOSFETs, therefore, it is considered that the gm with RF is dependent on stress-induced sub-band splitting of Si. The total gate capacitance (CG) extracted from scattering parameters increases (decreases) under tensile (compressive) stress for both n- and p-MOSFETs, which is explained by the variation of the effective mass perpendicular to the Si/SiO2 interface. The cut-off frequencies (fT) estimated from the gm and the CG varies in inverse proportion to the gate capacitance variation.

Evaluation of Spiral Inductors Embedded in Low Temperature Co-Fired Ceramic Substrates

In order to obtain full information on the high frequency performance of embedded passive elements, we design test elements group (TEG) substrates and compare the simulation result with measured data. S-parameters of spiral inductors embedded in low temperature co-fired ceramic (LTCC) substrates are simulated using high frequency structure simulator (HFSS), microwave studio (MWS) and advanced design simulator (ADS). Then effective inductance and Q factors are calculated from S-parameters after de-embedding process. Measurements of S-parameters are performed using a vector network analyzer in the frequency range up to 15 GHz. The simulation result with dimensional data measured by laser microscope and X-lay microscope is in good agreement with the experimental result. It is suggested that the simulation results can be applied to the design of system-in-a-package (SiP) substrate directly without making TEG.© 2005 ASME

Effects of Reactive Gas Compositions on the Magnetic Properties and Microstructures of FeTaNC Films

Soft magnetic properties and microstructure evolutions of FeTaNC films were investigated, and compared with those of FeTaN and FeTaC films. Effects of substrate species (glass vs. CaTiO 3 ) on the magnetic properties were also investigated. Co-addition of N and C enhances the grain refinements and soft magnetism compared with N or C only addition. Good soft magnetic characteristics of coercivity of 0.17 Oe, permeability of 4000 (5 MHz), and magnetic flux density of 17 kG can be obtained in the FeTaNC films with the relatively wide process ranges. While these values appear to be similar to those of FeTaN films on glass substrate, the most distinctive difference between FeTaNC and FeTaN (or C) films is the effects of substrate. Whereas FeTaNC films show good magnetic characteristics on both glass and CaTiO 3 substrates, FeTaN (or C) films show substantial degradation on the CaTiO 3 substrate.