The Conference on High Temperature Electronics

The status of and directions for high temperature electronics research and development were evaluated. Major objectives were to (1) identify common user needs; (2) put into perspective the directions for future work; and (3) address the problem of bringing to practical fruition the results of these efforts. More than half of the presentations dealt with materials and devices, rather than circuits and systems. Conference session titles and an example of a paper presented in each session are (1) User requirements: High temperature electronics applications in space explorations; (2) Devices: Passive components for high temperature operation; (3) Circuits and systems: Process characteristics and design methods for a 300 degree QUAD or AMP; and (4) Packaging: Presently available energy supply for high temperature environment

Design and characterisation of millimetre wave planar Gunn diodes and integrated circuits

Heterojunction planar Gunn devices were first demonstrated by Khalid et al in 2007. This new design of Gunn device, or transferred electron device, was based on the well-established material system of GaAs as the oscillation media. The design did not only breakthrough the frequency record of GaAs for conventional Gunn devices, but also has several advantages over conventional Gunn devices, such as the possibility of making multiple oscillators on a single chip and compatibility with monolithic integrated circuits. However, these devices faced the challenge of producing high enough RF power for practical applications and circuit technology for integration. This thesis describes systematic work on the design and characterisations of planar Gunn diodes and the associated millimetre-wave circuits for RF signal power enhancement. Focus has been put on improving the design of planar Gunn diodes and developing high performance integrated millimetre-wave circuits for combining multiple Gunn diodes. Improvement of device design has been proved to be one of the key methods to increase the signal power. By introducing additional δ-doping layers, electron concentration in the channel increases and better Gunn domain formation is achieved, therefore higher RF power and frequency are produced. Combining multiple channels in the vertical direction within devices is another effective way to increase the output signal power as well as DC-to-RF conversion efficiency. In addition, an alternative material system, i.e. In0.23Ga0.77As, has also been studied for this purpose. Planar passive components, such as resonators, couplers, low pass filters (LPFs), and power combiners with high performance over 100 GHz have been developed. These components can be smoothly integrated with planar Gunn diodes for compact planar Gunn oscillators, and therefore contribute to RF power enhancement. In addition, several new measurement techniques for characterising oscillators and passive devices have also been developed during this work and will be included in this thesis

Doped Metal Oxide High-K Gate Dielectric for Nonvolatile Memory and Light Emitting Applications

The zirconium-doped hafnium oxide (ZrHfO) high-k thin film has excellent gate dielectric properties, such as a higher crystallization temperature, a lower defect density, and a larger effective k value. As a promising high-k material, ZrHfO has been utilized for both nonvolatile memory (NVM) and light emitting applications. Replacing the polycrystalline Si floating gate, the discrete nanocrystals embedded ZrHfO gate dielectric can achieve promising NVM performance. On the other hand, warm white light can be emitted from the thermal excitation of nano-resistors form from the dielectric breakdown of the ZrHfO Metal-Oxide-Semiconductor (MOS) capacitor. This novel solid state incandescent light emitting device (SSI-LED) unveils a new concept for the lighting device evolution. Nanocrystalline cadmium sulfide (nc-CdS) embedded ZrHfO high-k NVMs have been fabricated to reduce the frequency dispersion problem caused by defects at the nanocrystal/dielectric interface. The nc-CdS embedded device can retain about 53% of originally trapped holes for 10 years and exhibit outstanding memory function at low operation voltage. The study on the nc-CdSe embedded ZrHfO NVMs shows that the high temperature enhances the hole trapping but decreases the electron trapping. Based on the different temperature dependences, the stored electrons release faster than stored holes. The raised temperature accelerates the dielectric breakdown process by increasing defect densities and defect effective conduction radii. The post deposition annealing (PDA) atmosphere is critical to the electrical and light emission characteristics of ZrHfO SSI-LEDs. It affects the dielectric breakdown, light emission intensity and efficiency by changing compositions of the high-k stack and the nano-resistor. The electrical properties, i.e., effective resistances and Schottky barrier heights of nano-resistors have been estimated. The nano-resistor behaves neither like a conductor nor like a semiconductor. Moreover, the barrier height inhomogeneity is observed due to the random and complicated nano-resistor formation. The embedding method and the heavily doped p-Si substrate have been employed to enhance the light emission from ZrHfO SSI-LEDs. Lastly, extensive applications of this novel nano-resistor device for on-chip optical interconnects and as diode-like anti-fuses have been discussed

Advanced III-Nitride Technology for mm-Wave Applications

Within wireless communication, there is a continuously growing need for more bandwidth due to an increasing number of users and data intense services. The development within sensor systems such as radars, is largely driven by the need for increased detection range and robustness. In such systems, power amplification and generation at high frequency are of importance. High-electron mobility transistors based on gallium nitride (GaN HEMTs) offer efficient generation of high output power at high frequency. This is enabled by the unique characteristics of GaN and its heterostructures, with a large breakdown field, related to the wide bandgap, and excellent electron transport properties. Due to this, it is today used in high-performing radar, telecommunications, as well as power electronic systems. Despite substantial progress over the last decade, the GaN HEMT is still the subject of intense research to reach its full potential. \ua0Recent development within epitaxy has significantly improved the quality of III-nitride semiconductors, and enabled indium aluminum nitride (InAlN) and InAlGaN as alternatives to AlGaN in the conventional AlGaN/GaN heterostructure. The higher polarization charge in these materials allows for considerable downscaling of the barrier layer thickness with a sustained high sheet carrier density. \ua0This has opened new possibilities for optimization of the high frequency performance. \ua0\ua0In this work, HEMTs with downscaled InAl(Ga)N barrier layers have been developed with the goal to optimize the devices for power amplification in the mm-wave range. Electron trapping and short-channel effects have been addressed in the design of the epi and in the optimization of the process modules. Different surface passivation layers and deposition methods have been evaluated to mitigate electron trapping at the surface. The output power density of a HEMT increased from 1.7 to 4.1 W/mm after passivation with a SiNx layer. The deposition method for Al2O3 passivation layers showed to have a profound impact on the electron trapping. A layer deposited by plasma-assisted atomic layer deposition (ALD) exhibited superior passivation of the surface traps as compared to the layer deposited by thermal ALD, resulting in an output power at 3 GHz of 3.3, and 1.9 W/mm, respectively. The effect of the channel layer thickness (50 – 150 nm) in InAlGaN/AlN/GaN HEMTs with and AlGaN back barrier demonstrated a trade-off between short-channel effects and deep-level electron trapping in the back barrier. The maximum output power was 5.3 W/mm at 30 GHz, obtained for a GaN layer thickness of 100 nm. To further enhance the high frequency performance, the ohmic contacts were optimized by the development of a Ta-based, Au free, metal scheme. Competitive contact resistance of < 0.2 Ωmm was achieved on both AlGaN/GaN and InAlN heterostructures with a Ta/Al/Ta metal stack. The contacts are annealed at a low temperature (550 – 575 \ubaC) compared to more conventional contact schemes, resulting in a smooth morphology and good edge acuity.\ua0 The implementation of microwave monolithic integrated circuits (MMICs) based on III-nitride HEMTs facilitate the use of III-nitride HEMTs in a system where frequency and compactness are key requirements. Thin film resistors (TFRs) are one of the passive components required in MMICs. In this work, a low-resistance titanium nitride (TiN) TFR was developed as a complement to the higher resistance tantalum nitride (TaN) TFR and mesa resistor in the in-house MMIC process. The developed TiN TFR exhibits a sheet resistance of 10 Ω/□, compared to 50 and 200-300 Ω/□ of the TaN TFR and semiconductor resistor, respectively. The critical dissipated power in the TFR showed a correlation to the footprint area, indicating that Joule-heating was the main cause of failure. TiN- and TaN films exhibit different signs of the thermal coefficient of resistance. This feature was used to demonstrate a temperature compensated TFR (TCR = -60 ppm \ubaC) with application in MMICs operating in a wide temperature range

Doped Metal Oxide High-K Gate Dielectric for Nonvolatile Memory and Light Emitting Applications

The zirconium-doped hafnium oxide (ZrHfO) high-k thin film has excellent gate dielectric properties, such as a higher crystallization temperature, a lower defect density, and a larger effective k value. As a promising high-k material, ZrHfO has been utilized for both nonvolatile memory (NVM) and light emitting applications. Replacing the polycrystalline Si floating gate, the discrete nanocrystals embedded ZrHfO gate dielectric can achieve promising NVM performance. On the other hand, warm white light can be emitted from the thermal excitation of nano-resistors form from the dielectric breakdown of the ZrHfO Metal-Oxide-Semiconductor (MOS) capacitor. This novel solid state incandescent light emitting device (SSI-LED) unveils a new concept for the lighting device evolution. Nanocrystalline cadmium sulfide (nc-CdS) embedded ZrHfO high-k NVMs have been fabricated to reduce the frequency dispersion problem caused by defects at the nanocrystal/dielectric interface. The nc-CdS embedded device can retain about 53% of originally trapped holes for 10 years and exhibit outstanding memory function at low operation voltage. The study on the nc-CdSe embedded ZrHfO NVMs shows that the high temperature enhances the hole trapping but decreases the electron trapping. Based on the different temperature dependences, the stored electrons release faster than stored holes. The raised temperature accelerates the dielectric breakdown process by increasing defect densities and defect effective conduction radii. The post deposition annealing (PDA) atmosphere is critical to the electrical and light emission characteristics of ZrHfO SSI-LEDs. It affects the dielectric breakdown, light emission intensity and efficiency by changing compositions of the high-k stack and the nano-resistor. The electrical properties, i.e., effective resistances and Schottky barrier heights of nano-resistors have been estimated. The nano-resistor behaves neither like a conductor nor like a semiconductor. Moreover, the barrier height inhomogeneity is observed due to the random and complicated nano-resistor formation. The embedding method and the heavily doped p-Si substrate have been employed to enhance the light emission from ZrHfO SSI-LEDs. Lastly, extensive applications of this novel nano-resistor device for on-chip optical interconnects and as diode-like anti-fuses have been discussed

Electrical properties and device applications of atomic layer deposited ZnO and GaN thin films

Ankara : The Department of Electrical and Electronics Engineering and The Graduate School of Engineering and Science of Bilkent University, 2014.Thesis (Master's) -- Bilkent University, 2014.Includes bibliographical references leaves 65-69.Zinc oxide (ZnO), a semiconducting material with a wide band gap of 3.37 eV, has become a promising material for wide range of electronic and optoelectronic applications. One of the most important properties of this material is its large exciton binding energy of 60 meV, which makes ZnO a strong candidate for ultraviolet light emitting diodes and lasers. In addition, potentially high electron mobility and the transparency in the visible region strengthen the future of the ZnO based transparent electronics. Although several applications of ZnO have taken their places in the literature, use of ZnO in the thermal imaging applications is yet to be explored. In the parts of this thesis related to ZnO, the temperature coefficient of resistance and electrical noise together with resistivity and contact resistance properties of atomic layer deposition based ZnO are investigated. Due to its remarkably high temperature coefficient of resistance value and suitable 1/f noise corner frequency, this material is proposed as an alternative material to be used in the active layers of uncooled microbolometers. GaN is another wide gap semiconductor which has been intensely investigated throughout the last decades for its potential usage in both optical and electrical applications. Especially, high saturation velocity of the electric carriers of this material has made it a strong candidate to be used in high power applications. Furthermore the high electron mobility transistors based on the 2-dimensional electron gas region formed between the AlGaN and GaN, have found wide range of applications in radio frequency (RF) electronics area. Currently, most commonly used techniques for growing GaN, are metal organic chemical vapor deposition and molecular beam epitaxy. Both of these techniques offer single crystalline layers; however, the process temperatures used in the growth of the GaN disable the use of this material in low temperature flexible electronic/optoelectronic applications. In order to solve this problem, hollow cathode plasma assisted atomic layer deposition technique is utilized and GaN thin films with polycrystalline structures are successfully grown at 200°C. In the parts of this thesis related to GaN, the electrical properties, the effect of contact annealing on the resistivity of the GaN thin films and the contact resistance between this material and Ti/Au metallization scheme are investigated. Afterwards, we present the world’s first thin film transistor with atomic layer deposition based GaN channel and discuss its electrical characteristics in detail. Finally, the GaN thin film transistors are fabricated by performing all fabrication steps at temperatures below 250°C. This is the lowest process thermal budget for the GaN based thin film transistors reported so far. Electrical characteristics as well as the stability of the proposed device are investigated and the results obtained are discussed. Proposed devices are believed to pave the way for the GaN-based stable flexible/transparent electronics after further materials and process optimization.Bolat, SamiM.S

Diode pumped Nd:YAG laser development

A low power Nd:YAG laser was constructed which employs GaAs injection lasers as a pump source. Power outputs of 125 mW TEM CW with the rod at 250 K and the pump at 180 K were achieved for 45 W input power to the pump source. Operation of the laser, with array and laser at a common heat sink temperature of 250 K, was inhibited by difficulties in constructing long-life GaAs LOC laser arrays. Tests verified pumping with output power of 20 to 30 mW with rod and pump at 250 K. Although life tests with single LOC GaAs diodes were somewhat encouraging (with single diodes operating as long as 9000 hours without degradation), failures of single diodes in arrays continue to occur, and 50 percent power is lost in a few hundred hours at 1 percent duty factor. Because of the large recent advances in the state of the art of CW room temperature AlGaAs diodes, their demonstrated lifetimes of greater than 5,000 hours, and their inherent advantages for this task, it is recommended that these sources be used for further CW YAG injection laser pumping work