Linfeng Zhang

The Electrical Behavior of Pd/AIN/Semiconductor Thin Film Hydrogen Sensing Structures

The device on Si substrates behaves as an MIS capacitor and the response to hydrogen is given by a shift of the capacitance vs. bias profile along the bias voltage axis, whereas the device on SiC behaves as a rectifying diode and the presence of hydrogen causes a shift of the forward current vs. voltage plot. The relatively large forward current, in both cases, indicates that there is measurable electrical transport across the AlN layer, but at the same temperature the turn on bias is different. Either structure contains two rectifying contacts in series, namely a Schottky contact between Pd and AlN and a heterojunction between AlN and the substrate.

The sensing mechanism and the response simulation of the MIS hydrogen sensor

The pure Pd and Pd alloy gated metal-insulator-semiconductor (MIS) hydrogen sensors have been studied. The chemical state of palladium in Pd and Pd alloy gated devices is similar and Pd alloy devices show a wide dynamic range. According to the hydrogen induced capacitance-voltage ( CV) shift and the response from a refreshed sensor, a new sensing mechanism is proposed that the hydrogen response is due to the protons on the metal/insulator interface and some of the protons take a long time to be desorbed from the interface. Based on this mechanism, a one-dimensional model is constructed with the consideration of the series resistance and fixed positive charges to simulate the CV/GV curves and hydrogen response from the Pd-Cr gated device.

The Sensing Mechanism and the Response Simulation of the MIS Hydrogen Sensor

The pure Pd and Pd alloy gated metal-insulator-semiconductor (MIS) hydrogen sensors have been studied. The chemical state of palladium in Pd and Pd alloy gated devices is similar and Pd alloy devices show a wide dynamic range. According to the hydrogen induced capacitance-voltage ( CV) shift and the response from a refreshed sensor, a new sensing mechanism is proposed that the hydrogen response is due to the protons on the metal/insulator interface and some of the protons take a long time to be desorbed from the interface. Based on this mechanism, a one-dimensional model is constructed with the consideration of the series resistance and fixed positive charges to simulate the CV/GV curves and hydrogen response from the Pd-Cr gated device.

Residual Stresses in TiO 2 Anatase Thin Films Deposited on Glass, Sapphire and Si Substrates

Anatase-TiO2 films (thickness 100-1000 nm) were grown on glass, sapphire, and Si(100) substrates using pulsed dc-magnetron reactive sputtering. By measuring the curvature of substrates before and after the thin film deposition, the residual stresses were determined. These results clearly show that the bi-axial stresses are compressive type and decreases with the increasing film thickness. The Raman spectra of these films were measured with two different excitation wavelengths (514 and 785 nm) and the thickness dependent shifts of Eg phonon mode were studied. The dominant 144 cm -1 Eg mode in TiO2 anatase clearly shifts to a higher value by 0.45 to 17.4 cm -1 depending on the type of substrate and the thickness of the film. Maximum shift was seen for the films on glass substrate indicating a higher bi-axial compressive stress in agreement with the curvature measurements. The excitation wavelength dependent shift of Eg mode clearly shows that the bi-axial stress increases along the film depth, being larger at the film/substrate interface.