Chih-Yao Wang

Characterization on pH sensing performance and structural properties of gadolinium oxide post-treated by nitrogen rapid thermal annealing

A detail investigation on the pH sensing performance of Gd2O3 layer was proposed in this work. Electrolyte–insulator–semiconductor (EIS) structure with Gd2O3 layer deposited directly on silicon by reactive radio frequency sputtering with Gd target was chosen as the testing platform. The postdeposition rapid thermal annealing (RTA), performed at various temperatures for 1 min in N2 ambience, was first used to improve the pH sensing performance of Gd2O3. With RTA treatment at 800 °C, pH sensitivity of Gd2O3 EIS structure can be increased from 35.5 mV/pH to 55 mV/pH. This behavior can be explained by the increase of surface sites, which is supported by atomic force microscopy analysis. With RTA treatment at 700 °C and 800 °C, the drift coefficient for Gd2O3 layer was reduced to 0.03 and 1.2 mV/h, which is resulted from the densification of Gd2O3 layer supported by x-ray photoemission spectrometry. Therefore, Gd2O3 layer with RTA in N2 ambience at 700 °C or 800 °C could be a potential candidate for pH-sensiti...

Chemical sensing properties of electrolyte/SiGe/SiO2/Si structure

To investigate the surface properties of silicon germanium (SiGe) as a chemically sensitive membrane, SiGe layers deposited at Si2H6 and GeH4 ambience by low-pressure chemical-vapor-deposition (LPCVD) at 475 °C were prepared. First, the effect of ac measuring frequency on capacitance–voltage (C–V) curves obtained from a SiGe electrolyte–insulator–semiconductor (EIS) structure was studied. The pH sensitivity of SiGe-EIS structure was 59.8 mV/pH, calculated from reference voltages in the pH range from 10 to 2. A voltage shift was observed in the same pH buffer solution for different measurement loops. To analyze the depth profile of a SiGe membrane, Auger electron spectroscopy (AES) was used. The formation of a native oxidation layer on the surface of SiGe was observed, and the layer had a thickness of 20 A.

The surface site dehydration mechanism for Si/sub 3/N/sub 4/ sensing membrane by post-baking treatment

This work presented a post-baking treatment effect on Si/sub 3/N/sub 4/ sensing membrane for the pH response. Special measurement sequences were proposed to verify the surface site activation and de-hydration. Sensitivity was improved by pH4 buffer solution immersion. However, sensitivities were decreased 3-8.5 mV/pH and 1-2.8mV/pH by first and second baking cycle respectively. Higher baking temperature made the sensitivity decrease more. It was due to ion and surface site exchange and repaired the dangling bond on sensing membrane during buffer immersion. The post-baking treatment broke some active sites by thermal energy. The higher baking temperature provided more thermal energy to break active sites and degrade more sensitivity. A novel physical model was proposed for the activation and dehydration behavior.

Ion sensing improvements of hafnium oxide by nitrogen incorporation

This is the first time that hafnium oxynitride (HfO/sub x/N/sub y/) have been applied to hydrogen ion sensing technology. HfO/sub x/N/sub y/ and HfO/sub 2/ were prepared in different ratio Ar/N/sub 2//O/sub 2/ gas mixture by sputter with hafnium target. The sensitivity for all samples could be improved for at least 3.3mV/pH by 12 hours R.O. water immersion. The optimized condition for HfO/sub x/N/sub y/-EIS was sputtering in the ambient of N/sub 2/ ratio 10% and achieved highest sensitivity (56.64mV/pH) and lowest drift (1.42mV/hr) and hysteresis (1.7mV). This material and process could also improve membrane thermal stability and integrate easily with standard CMOS process.

Nitrogen effects on the sensitivity of tantalum nitride (Ta/sub x/N) for ion sensing devices

A novel approach was proposed in this work for hydrogen ion sensing with tantalum nitride (Ta/sub x/N). Ta/sub x/N sensing membrane was sputtered by mixture gas which gas ratio was modified during the sputtering, from 6 to 20 % with Ar and nitrogen mixture gas for tantalum (Ta) target. The optimized condition for Ta/sub x/N-EIS structure improved the sensitivity to 50.47 mV/pH under 16% nitrogen mixture gas ratio. However sensitivity of all nitrogen ratio conditions could be improved for several mV/pH after 8 hours R.O. water immersion. Hysteresis width also changed with different nitrogen ratio and the minimum hysteresis was 5mV/pH at 12% nitrogen ratio. Due to the large variation of sensitivity and high linearity, the nitrogen ratio modification sputtering is suitable for employ TaN to high sensitivity ISFET and low sensitivity REFET application respectively.