Amorphous ultra-wide bandgap ZnOx thin films deposited at cryogenic temperatures

Crystalline wurtzite zinc oxide (w-ZnO) can be used as a wide band gap semiconductor for light emitting devices and for transparent or high temperature electronics. The use of amorphous zinc oxide (a-ZnO) can be an advantage in these applications. In this paper we report on X-ray amorphous a-ZnOx thin films (~500 nm) deposited at cryogenic temperatures by reactive magnetron sputtering. The substrates were cooled by a nitrogen flow through the copper substrate holder during the deposition. The films were characterized by X-ray diffraction (XRD), Raman, infrared, UV-Vis-NIR spectroscopies, and ellipsometry. The a-ZnOx films on glass and Ti substrates were obtained at the substrate holder temperature of approximately -100 oC. New vibration bands at 201, 372, and 473 cm-1 as well as O-H stretch and bend absorption bands in the a-ZnOx films were detected by FTIR spectroscopy. Raman spectra showed characteristic ZnO2 peaks at 386 and 858 cm-1 attributed to the peroxide ion O22- stretching and libration modes, respectively. In addition, the films contain neutral and ionized O2 and O2- species. The a-ZnOx films are highly transparent in the visible light range (approx. 87%) and exhibit a refractive index of 1.68 at 2.25 eV (550 nm). An optical band gaps is 4.65 eV with an additional band edge absorption feature at 3.50 eV. It has been shown that the deposition on actively cooled substrates can be a suitable technique to obtain low temperature phases that cannot be deposited at room temperature.Comment: 24 pages, 8 figure

A Very Low-Complexity 0.3-4.4 GHz 0.004 mm2 All-Digital Ultra-Wide-Band Pulsed Transmitter for Energy Detection Receivers

This paper presents a very low-complexity all-digital IR-UWB transmitter that can generate pulses in the band 0-5 GHz, requiring a silicon area lower than a PAD for signal I/O. The trans- mitter, suited to non-standardized low data rate applications, is prototyped in a 130 nm RFCMOS technology and includes analog control signals for frequency and bandwidth tuning. Center fre- quency is linearly selected with voltage supply, 0.5 V for the range 0-960 MHz and 1.1 V supply for the higher 3.1-5 GHz range. The architecture is based on the same delay cell for both baseband and radio frequency signal generation and pulses fractional bandwidth remains constant when voltage supply and control voltages scale. At 420 MHz center frequency, the transmitter achieves 7 pJ/pulse, and for 4 GHz center frequency pulses, it achieves 32 pJ/pulse ac- tive energy consumption. The OOK/S-OOK transmitter occupies an area of 0.004 mm . For ASK modulation, the system includes a separate on-chip capacitor bank connected to the output of the transmitter for an overall size of 0.024mm2. For pulse rates below 100 kpps, the generated pulses meet the FCC indoor mask with an off-chip DC block capacitor. The paper also presents over-the-air measurements using a planar monopole antenna operating in the 1.5-3.7 GHz frequency rang

Reactive pulsed direct current magnetron sputtering deposition of semiconducting yttrium oxide thin film in ultralow oxygen atmosphere: A spectroscopic and structural investigation of growth dynamics

An experimental investigation was conducted to explore spectroscopic and structural characterization of semiconducting yttrium oxide thin film deposited at 623 K (+/- 5K) utilizing reactive pulsed direct current magnetron sputtering. Based on the results obtained from both x-ray diffraction and transmission electron microscope measurements, yttrium monoxide is very likely formed in the transition region between {\beta}-Y2O3 and {\alpha}-Y2O3, and accompanied by the crystalline Y2O3. Resulting from either the low energy separation between 4d and 5s orbitals and/or different spin states of the corresponding orbitals' sublevels, the stability of monoxide is most presumably self-limited by the size of the crystal in thermodynamic terms. This behavior develops a distortion in the structure of the crystal compared to the metal oxide cubic structure and it also effectuates the arrangement in nanocrystalline/amorphous phase. In addition to this, spectroscopic ellipsometry denotes that the semiconducting yttrium oxide has the dominant, mostly amorphous, formation character over crystalline Y2O3. Our purpose, by means of the current findings, is to advance the understanding of formation kinetics/conditions of yttrium with an unusual valency (2+)