Fabrication and Electrical characteristic of quaternary ultrathin HfTiErO thin films for MOS devices grown by rf sputtering

Ultra-thin Ti and Er co-doped HfO2 films were grown on Si substrate by RF sputtering at different compositions and subjected to rapid thermal annealing at 500?°C and 700?°C in nitrogen ambient for 60 s. Dielectric properties of ultrathin co doped with Tritium and Erbium into hafnium oxide (HfO2) with rapid thermal annealing (RTA) have been investigated. Ti and Er different contents doped HfO2 thin films about (5 to 10) nm thicknesses have been employed for Au/HfTiErO/Si/Au metal oxide semiconductor (MOS) structures fabrication. The fabricated MOS (Au/HfTiErO/Si/Au) structure has been used for extracting electrical properties such that, dielectric constant, effective charge carriers, flat band voltage, interface trap density and doping concentration through capacitance voltage measurements. The films compared at different contents used for Ti and Er doped with HfO2 on growth parameters, which could not showed excellent properties due to small thickness and other several defects during the depositions. While, the film annealed at 500?°C has the improved microstructure and electrical characteristics. Furthermore Atomic force microscopy and X-ray photo electron microscopy analysis verified the microstructure of HfTiErO gate oxide for future MOS devices.   Keywords: high-k, HfTiErO, Thin films, rf Sputterin

Plasma-nitrided Ga2O3(Gd2O3) as interfacial passivation layer for InGaAs metal-oxide-semiconductor capacitor with HfTiON gate dielectric

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Novel Semiconductor Materials for Mid-Infrared Optoelectronic Application

Thin film gallium antimony bismuth (GaSbBi) grown on GaSb substrate via molecular beam epitaxy (MBE) have been explored in this thesis by characterising the films electrical, physical and optical properties. From these wafers Schottky diodes, and metal-semiconductor-metal photodetectors (MSM-PDs) have been investigated. Another promising material for infrared photodetectors is InAs, in this work the use of high-k based dielectrics has been investigated to improve the passivation of InAs avalanche photodiodes (APDs). Initially, the influence of postgrowth thermal annealing on GaSbBi Schottky barrier diodes has been investigated. The I-V characteristics indicated a better ideality factor and less leakage current at the reverse bias, as the annealing temperature increased up to 500 °C for a duration of 30 min. X-ray diffraction and scanning transmission electron microscope measurements were performed to verify that the bismuth composition was unaffected during the annealing process. Energy dispersive x-ray analysis indicated that Sb clustering occurs at high annealing temperatures, resulting in a concomitant degradation in the electrical performance. The optimum electrical characteristics of the diode were obtained with an annealing temperature of 500 °C for 30 min, resulting in an ideality factor of 1.3 being achieved. The optimised GaSbBi and GaSbN samples were then fabricated into MSM-PDs and verify the viability of using GaSbBi and GaSbN as active layers in photodetector. The cut-off wavelength extended to 1950 nm (2.9% Bi), 1990 nm (3.8% Bi), 2080 nm (4.5% Bi) and 2190 nm (1.5% N) have been observed, demonstrating the viability of using Bi and N for mid-infrared sensing. The comparison of different geometry on the photo spectral response indicating Bi incorporation increase the lattice expansion, which reduce the carrier concentration of the devices. Optimization of InAs based APDs are reported in this thesis. The use of high-k dielectric material as a passivation layer to improve the performance of InAs APDs are discussed. Three potential passivation layers, including ZnO, Al2O3 and MgO have been identified, all of which enables the suppression of surface leakage in smaller sized InAs APDs with a radius of 50 ìm and at lower temperatures of 175 K compared to a reference SU8 device. The influence of repeated temperature cycling on these layers has also been investigated with ZnO observed clear degradation after ten cycle, MgO shows almost a 10% higher current at a constant voltage after ten temperature cycles and Al2O3 passivated device, exhibiting no change in performance after temperature cycles. Suggesting Al2O3 as an effective and stable material for InAs APDs

Towards A Graphene Chip System For Blood Clotting Disease Diagnostics

Point of care diagnostics (POCD) allows the rapid, accurate measurement of analytes near to a patient. This enables faster clinical decision making and can lead to earlier diagnosis and better patient monitoring and treatment. However, despite many prospective POCD devices being developed for a wide range of diseases this promised technology is yet to be translated to a clinical setting due to the lack of a cost-effective biosensing platform.This thesis focuses on the development of a highly sensitive, low cost and scalable biosensor platform that combines graphene with semiconductor fabrication tech-niques to create graphene field-effect transistors biosensor. The key challenges of designing and fabricating a graphene-based biosensor are addressed. This work fo-cuses on a specific platform for blood clotting disease diagnostics, but the platform has the capability of being applied to any disease with a detectable biomarker.Multiple sensor designs were tested during this work that maximised sensor ef-ficiency and costs for different applications. The multiplex design enabled different graphene channels on the same chip to be functionalised with unique chemistry. The Inverted MOSFET design was created, which allows for back gated measurements to be performed whilst keeping the graphene channel open for functionalisation. The Shared Source and Matrix design maximises the total number of sensing channels per chip, resulting in the most cost-effective fabrication approach for a graphene-based sensor (decreasing cost per channel from £9.72 to £4.11).The challenge of integrating graphene into a semiconductor fabrication process is also addressed through the development of a novel vacuum transfer method-ology that allows photoresist free transfer. The two main fabrication processes; graphene supplied on the wafer “Pre-Transfer” and graphene transferred after met-allisation “Post-Transfer” were compared in terms of graphene channel resistance and graphene end quality (defect density and photoresist). The Post-Transfer pro-cess higher quality (less damage, residue and doping, confirmed by Raman spec-troscopy).Following sensor fabrication, the next stages of creating a sensor platform involve the passivation and packaging of the sensor chip. Different approaches using dielec-tric deposition approaches are compared for passivation. Molecular Vapour Deposi-tion (MVD) deposited Al2O3 was shown to produce graphene channels with lower damage than unprocessed graphene, and also improves graphene doping bringing the Dirac point of the graphene close to 0 V. The packaging integration of microfluidics is investigated comparing traditional soft lithography approaches and the new 3D printed microfluidic approach. Specific microfluidic packaging for blood separation towards a blood sampling point of care sensor is examined to identify the laminar approach for lower blood cell count, as a method of pre-processing the blood sample before sensing.To test the sensitivity of the Post-Transfer MVD passivated graphene sensor de-veloped in this work, real-time IV measurements were performed to identify throm-bin protein binding in real-time on the graphene surface. The sensor was function-alised using a thrombin specific aptamer solution and real-time IV measurements were performed on the functionalised graphene sensor with a range of biologically relevant protein concentrations. The resulting sensitivity of the graphene sensor was in the 1-100 pg/ml concentration range, producing a resistance change of 0.2% per pg/ml. Specificity was confirmed using a non-thrombin specific aptamer as the neg-ative control. These results indicate that the graphene sensor platform developed in this thesis has the potential as a highly sensitive POCD. The processes developed here can be used to develop graphene sensors for multiple biomarkers in the future

Effects of Ti content and wet-N2 anneal on Ge MOS capacitors with HfTiO gate dielectric

Thin HfTiO gate dielectric is deposited by reactive co-sputtering method followed by wet or dry N2 anneal. The effects of Ti content on the performance of HfTiO gate dielectric are investigated by using different sputtering powers for the Ti target. Experimental results indicate that as the Ti content increases, the dielectric constant (κ) can increase up to 40 for a Ti content of 28%. However, when the Ti content is too high, the interface properties and gate leakage properties are deteriorated. On the contrary, results show that owing to the hydrolyzable property of GeOx, the wet-N2 anneal can greatly suppress the growth of unstable low-κ GeOx interlayer, resulting in lower interface-state density and gate leakage current, in addition to larger κ value. In this study, when the sputtering power of the Ti target is 80 W together with a 25-W power for the Hf target and a post-deposition anneal (PDA) in wet-N2 ambient at 500 °C for 300 s, excellent device performance is achieved: equivalent oxide thickness of 0.72 nm, equivalent dielectric constant of 39, interface-state density of 6.5 × 1011 eV-1 cm-2 and gate leakage current of 5.7 × 10-4 A/cm2 at Vg = 1 V. Therefore, in order to obtain high-quality HfTiO gate dielectric for small-scaled Ge MOS devices, not only should the Ti content be optimized, the PDA should also be done in a wet-N2 ambient. © 2007 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex