Shiau-Shin Cheng

Anomalous p-channel amorphous oxide transistors based on tin oxide and their complementary circuits

In this article, we report the fabrication of SnO2 thin film transistors (TFTs) fabricated by reactive evaporation. Different from the previous reports, the fabricated TFTs exhibit p-type conductivity in its undoped form. The postdeposition annealing temperature was tuned to achieve p-channel SnO2 TFTs. The on/off ratio and the field-effect mobility were ∼103 and 0.011cm2∕Vs, respectively. To demonstrate inverter circuit, two devices with different threshold voltages were combined and an output gain of 2.8 was achieved. The realization of p-channel oxide TFTs would open up new challenges in the area of transparent electronics.

Dependence of channel thickness on the performance of In2O3 thin film transistors

Bottom gate and top contact thin film transistors were fabricated using In2O3 thin films as active channel layers. Thin films of varying thicknesses in the range 5?20?nm were deposited on an SiO2 gate dielectric by the thermal evaporation process in the presence of high purity oxygen. The results of atomic force microscopy show that all the films exhibit dense grain distribution with a root-mean-square roughness in the range 0.6?8.0?nm. Irrespective of the thickness of the channel layer, the on/off ratio of the device is 104. The channel mobility and resistivity were found to be a strong function of the thickness of the active layer. The Levinson model was used to calculate the trap density and the grain boundary mobility. The low processing temperature shows the possibility of utilizing these devices on flexible substrates such as polymer substrates.

Vertical organic triodes with a high current gain operated in saturation region

The authors report the fabrication of vertical organic triodes operated in the pronounced saturation regions by using two back-to-back pentacene Schottky diodes. The device with an optimized 0.7nm LiF hole injection enhancement layer and a 70nm pentacene emitter can achieve an ultrahigh common-emitter current gain of 48 in the saturation region at a low applied voltage VCE of −4V and a base current density of 0.25mA∕cm2. In addition, the device exhibits a high output current density of 12.1mA∕cm2 and a high on/off current ratio of 103.

Influence of thin metal base thickness on the performance of CuPc vertical organic triodes

In this letter, the characteristics of vertical organic triodes fabricated by using two copper phthalocyanine (CuPc) back-to-back Schottky diodes with different metal base thicknesses are reported. The vertical organic triodes exhibit pronounced saturation regions in the output current-voltage characteristics. The common-emitter current gain reduces with increasing the Al base thickness due to the increase of recombination current at the base end resulted from the reduction of opening voids in the Al metal film. The common-emitter current gain of the device with 4.5nm thick Al base reaches 1.9 at VCE=−6V and JB=2.5mA∕cm2.

Pentacene Thin-Film Transistor with PVP-Capped High-k MgO Dielectric Grown by Reactive Evaporation

Pentacene thin-film transistors operated at low voltages have been realized by employing hybrid dielectrics, poly(4-vinylphenol) (PVP)-capped MgO. The MgO film was deposited by reactive evaporation of magnesium in oxygen. The PVP layer plays a role in modifying the surface morphology of the MgO layer, and the images of atomic force microscopy for the PVP-capped MgO films show a root-mean-square roughness of 1 nm. The hybrid dielectric has a dielectric constant of 7.05 with a dielectric strength. The fabricated pentacene organic thin-film transistors exhibit a mobility of 0.66 cm 2 /V s, a threshold voltage of -2.67 V, and an on/off ratio of 10 3 .

All-organic hot-carrier triodes with thin-film metal base

In this letter, the authors investigate the promising vertical-type triodes based on small organic molecules and the related hot-carrier transport. The devices show transistorlike characteristics, in which output current can be modulated by demanding different input currents on their thin metal base electrodes. By using pentacene for the channel layer material and N,N′-di(naphthalen-l-yl)-N,N′-diphenyl-benzidine for the carrier energy-enhancing layer, the vertical-type hot carrier triodes exhibit a good current saturation with current gain of 2.38 for both the common-base and common-emitter configurations. The mechanism of operation is proposed and examined by the basic electrical measurements.

Evolution of structural order in germanium ion-implanted amorphous silicon layers

High-resolution transmission electron microscopy in conjunction with autocorrelation function analysis have been applied to investigate the evolution of structural order in germanium ion-implanted amorphous silicon (a-Si) layers. A high density of Si nanocrystallites as small as 1 nm in size was detected in as-implanted a-Si layers. The density of embedded nanocrystalline Si was found to diminish in a-Si layers with annealing temperature first then increase. The results are discussed in the context of free energy change with annealing temperature.

POLARITY EFFECT ON FAILURE OF NI AND NI2SI CONTACTS ON SI

Stability of contacts in shallow junction devices against high current density is a reliability issue for very large scale integration technology. We have observed a strong polarity effect on failure at nickel and nickel silicide contacts on both n- and p-type Si under high stress conditions. In a pair of cathode and anode contacts the Ni/n+-Si contact pair fails at the anode, while the Ni/p+-Si pair fails at the cathode. The Ni/Ni2Si/n+-Si and Ni/Ni2Si/p+-Si were found to fail preferentially at the cathode. Microbeam Rutherford backscattering spectrometry and Auger electron spectroscopy depth profiles show that a silicide reaction occurs between Ni and Si during current stressing, especially at the failed contacts. In situ resistance data indicate that the resistance of the failed contact increases with time while that of the other contact in the pair remains constant. Transmission electron microscopy shows that the silicide formation is not uniform at the damaged contacts. A mixture of dominant epitaxia...

Formation of C54–TiSi 2 in titanium on nitrogen-ion-implanted (001)Si with a thin interposing Mo layer

Formation of TiSi 2 in titanium on nitrogen-implanted (001)Si with a thin interposing Mo layer has been investigated. The presence of a Mo thin interposing layer was found to decrease the formation temperature of C54–TiSi 2 by about 100 °C. A ternary (Ti, Mo)Si 2 phase was found to distribute in the silicide layer. The ternary compound is conjectured to provide more heterogeneous nucleation sites to enhance the formation of C54–TiSi 2 . On the other hand, the effect of grain boundary for decreasing transformation temperature was found to be less crucial. For Ti/Mo bilayer on 30 keV BF 2 + or As + + 20 keV, 1 × 10 15 /cm 2 N 2 + implanted samples, a continuous C54–TiSi 2 layer was found to form in all samples annealed at 650–950 °C. The presence of nitrogen atoms in TiSi 2 is thought to lower the silicide/silicon interface energy and/or the silicide surface energy to maintain the integrity of the C54–TiSi 2 layer at high temperatures.

Kinetics of Cu3Ge formation and reaction with Al

Cu3Ge films have been found to have a low resistivity, good adhesion on SiO2, good thermal stability on Si, and good oxidation resistance. It has the potential as an ideal adhesion/barrier/passivation layer for Cu ultralarge scale integration metallization. The kinetics of Cu3Ge formation and the thermal stability of Cu3Ge against Al were studied by in situ resistivity measurement, Rutherford backscattering spectrometry, and transmission electron microscopy. We found that Cu reacted with Ge in the temperature range of 100–200 °C. The activation energy of the Cu–Ge compound formation was found to be 1.1±0.1 eV. The Cu–Ge compound was identified as e-Cu3Ge from transmission electron microscope diffraction patterns. Upon annealing the e-Cu3Ge became unstable on Al at the temperature range of 300–350 °C. In the reaction between Al and Cu3Ge, Cu preferentially reacted with Al to form an e-Al2Cu3 compound. The activation energy of formation of the Al–Cu compound was found to be 2.1±0.1 eV.