Creation and Optimisation of Plasma Etch Processes for the Manufacture of Silicon Microstructures

Microneedles are an area of growing interest for applications in transdermal delivery. Small, minimally invasive medical or cosmetic devices, microneedles are intended to penetrate the skin’s outer protective layer (stratum corneum) to facilitate delivery of active formulations into the skin. Delivery of solution via microneedles has the benefits associated with hypodermic injection, i.e. avoiding the first-pass metabolism systems, with the added advantages of painless delivery and dose sparing from the reduced solution volumes required.Advancements in semiconductor processing technologies and equipment have enabled the creation of devices and structures that could not have been fabricated in the past. This is also true for the fabrication of microneedles, where previous manufacturing methods have relied on hazardous chemicals such as Hydrofluoric Acid and Potassium Hydroxide to create the sharp tip of the needle, required to reduce insertion force.In this thesis, the realisation of a hollow bevelled silicon microneedle fabricated using only plasma processing techniques is presented, providing a route to scalable manufacture of high-performance, sharp-tipped microneedles. The microneedle fabrication process consists of three main etch steps in the process flow to create hollow structures. For each of the Bevel, Bore, and Shaft processes the development and optimisation is detailed. Throughout the process development, several unexpected processing issues were encountered, including depth non-uniformity, “notching”, and “silicon grass”. Investigations have been performed to determine the root cause of each issue and fine-tune processes to optimise the final devices. A discussion of the process hardware is also presented, with reference to the benefits for each specific application process.Following development and optimisation of each individual process, the Bevel, Bore, and Shaft processes were integrated in the manufacturing flow to create the final hollow silicon microneedle device. Issues arising from the combination of the three processes have been investigated, resolved, and optimised. This includes the conception and execution of a novel process for the plasma smoothing of an angled silicon surface, which improved the quality of lithography on the non-planar bevel surface and minimised grass formation.Preliminary testing, undertaken to assess the suitability of these devices for transdermal use, included mechanical fracture force, skin penetration, and injection testing. The microneedles were found to be strong enough to remain intact during insertion, and demonstrate successful penetration and injection through the stratum corneum and into the deeper skin layers

Ultra-thin silicon technology for tactile sensors

In order to meet the requirements of high performance flexible electronics in fast growing portable consumer electronics, robotics and new fields such as Internet of Things (IoT), new techniques such as electronics based on nanostructures, molecular electronics and quantum electronics have emerged recently. The importance given to the silicon chips with thickness below 50 μm is particularly interesting as this will advance the 3D IC technology as well as open new directions for high-performance flexible electronics. This doctoral thesis focusses on the development of silicon–based ultra-thin chip (UTC) for the next generation flexible electronics. UTCs, on one hand can provide processing speed at par with state-of-the-art CMOS technology, and on the other provide the mechanical flexibility to allow smooth integration on flexible substrates. These development form the motivation behind the work presented in this thesis. As the thickness of any silicon piece decreases, the flexural rigidity decreases. The flexural rigidity is defined as the force couple required to bend a non-rigid structure to a unit curvature, and therefore the flexibility increases. The new approach presented in this thesis for achieving thin silicon exploits existing and well-established silicon infrastructure, process, and design modules. The thin chips of thicknesses ranging between 15 μm – 30 μm, were obtained from processed bulk wafer using anisotropic chemical etching. The thesis also presents thin wafer transfer using two-step transfer printing approach, packaging by lamination or encapsulation between two flexible layerand methods to get the electrical connections out of the chip. The devices realised on the wafer as part of front-end processing, consisted capacitors and transistors, have been tested to analyse the effect of bending on the electrical characteristics. The capacitance of metal-oxide-semiconductor (MOS) capacitors increases by ~5% during bending and similar shift is observed in flatband and threshold voltages. Similarly, the carrier mobility in the channel region of metal-oxide-semiconductor field effect transistor (MOSFET) increases by 9% in tensile bending and decreases by ~5% in compressive bending. The analytical model developed to capture the effect of banding on device performance showed close matching with the experimental results. In order to employ these devices as tactile sensors, two types of piezoelectric materials are investigated, and used in extended gate configuration with the MOSFET. Firstly, a nanocomposite of Poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-TrFE) and barium titanate (BT) was developed. The composite, due to opposite piezo and pyroelectric coefficients of constituents, was able to suppress the sensitivity towards temperature when force and temperature varied together, The sensitivity to force in extended gate configuration was measured to be 630 mV/N, and sensitivity to temperature was 6.57 mV/oC, when it was varied during force application. The process optimisation for sputtering piezoelectric Aluminium Nitride (AlN) was also carried out with many parametric variation. AlN does not require poling to exhibit piezoelectricity and therefore offers an attractive alternative for the piezoelectric layer used in devices such as POSFET (where piezoelectric material is directly deposited over the gate area of MOSFET). The optimised process gave highly orientated columnar structure AlN with piezoelectric coefficient of 5.9 pC/N and when connected in extended gate configuration, a sensitivity (normalised change in drain current per unit force) of 2.65 N-1 was obtained

High-Density Solid-State Memory Devices and Technologies

This Special Issue aims to examine high-density solid-state memory devices and technologies from various standpoints in an attempt to foster their continuous success in the future. Considering that broadening of the range of applications will likely offer different types of solid-state memories their chance in the spotlight, the Special Issue is not focused on a specific storage solution but rather embraces all the most relevant solid-state memory devices and technologies currently on stage. Even the subjects dealt with in this Special Issue are widespread, ranging from process and design issues/innovations to the experimental and theoretical analysis of the operation and from the performance and reliability of memory devices and arrays to the exploitation of solid-state memories to pursue new computing paradigms

Transfer printing based microassembly and colloidal quantum dot film integration

Micro / nanoscale manufacturing requires unique approaches to accommodate the immensely different characteristics of the miniscule objects due to their high surface area to volume ratio when compared with macroscale objects. Therefore, surface forces are much more dominating than body forces, which causes the significant difficulty of miniscule object manipulation. Because of this challenge, monolithic microfabrication relying on photolithography has been the primary method to manufacture micro / nanoscale structures and devices in place of microassembly. However, by virtue of the two-dimensional (2D) nature of photolithography, formation of complex 3D shape architectures via monolithic microfabrication is inherently limited, which would otherwise enable improvements in performance and novel functionalities of devices. Furthermore, monolithic microfabrication is compatible only with materials which survive in a wet condition during photolithography. Delicate nanomaterials such as colloidal quantum dots cannot be processed via monolithic microfabrication. In this context, transfer printing has emerged as a method to transfer heterogeneous material pieces from their mother substrates to a foreign substrate utilizing a polymeric stamp in a dry condition. In this thesis, advanced modes of transfer printing are studied and optimized to enable a 3D microassembly called ‘micro-Lego’ and a novel strategy of quantum dot film integration. Micro-Lego involves transfer printing for material piece pick-and-place and thermal joining for irreversible permanent bonding of placed material pieces. A microtip elastomeric stamp is designed to advance transfer printing and thermal joining processes are optimized to ensure subsequent material bonding. The mechanical joining strength between material pieces assembled by micro-Lego are characterized by means of blister tests and the nanoindentation. Moreover, the electrical contact between two conducting materials formed by micro-Lego are examined. Lastly, inspired from the subtractive transfer printing technique, protocols of quantum dot film patterning using polymeric stamps made of a shape memory polymer as well as a photoresist are established for the convenient integration of quantum dots in various geometries and configurations as desired. Transfer printing-based micro / nanoscale manufacturing presented in this thesis opens up new pathways to manufacture not only complex 3D functional micro devices but also high resolution nano devices for unparalleled performance or for an unusual functionality, which are unattainable through monolithic microfabrication

GaN-on-Si 기반의 고주파/고전력 소자의 제작 및 특성 분석

학위논문 (박사)-- 서울대학교 대학원 : 전기·정보공학부, 2016. 2. 서광석.Owing to the unique capabilities of achieving high current density, high breakdown voltage, high cut-off frequency and high operating temperature, AlGaN/GaN high electron mobility transistors (HEMTs) are emerging as promising candidates for RF power amplifier and power switching devices. Nevertheless, despite the great potential of these new technologies, they still suffer from physical and fabrication issues which may prevent devices fabricated on GaN from achieving the performance required. This thesis presents a comprehensive study on the development of GaN-based high frequency, high power transistors. This work can be divided into two parts, namely D-mode AlGaN/GaN schottky HEMTs on silicon substrate for high power X-band operation and E-mode Si3N4/AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) for power switching devices. One of the main obstacle is the trapping effects, may be exacerbated when devices are operated in Radar systems. In this work, we will use a novel fluoride-based plasma treatment technique to reduce trapping phenomenon which originated from the surface, and then apply this treatment technique in conjunction with a field plate structure to a device for GaN-based RF applications. To improve overall device performance, a backend process with individually grounded source via formation has been developed to integrate large periphery devices. Based upon it, GaN HEMT amplifier with single chip of 3.6 mm gate periphery has been successfully developed. It exhibits very high power density of 8.1 W/mm with 29.4 W output power under VDS = 38 V pulse operating condition. Compared to the conventional depletion-mode AlGaN/GaN (D-mode), Enhancement mode (E-mode) devices are attracting a great interest as they allow simplistic circuity and safe operation. It is difficult to obtain E-mode operation with a low on-resistance and a high breakdown voltage. A gate recess technique will be crucial to realize an enhancement-mode operation and improve the transfer characteristics. To reduce the on resistance and enhance the drain current density, partially recessed MIS-HFETs are investigated. The gate recess was carried out using a low-damage Cl2/BCl3-based RIE where the target etch depth was remains AlGaN barrier layer in order to improve the transfer characteristics. The occurring degradation of the mobility due to plasma etching-induced damage and scattering effect were effectively removed by partial gate recess technique. The technologies we developed have helped to give definitive direction in developing GaN-based high frequency, high power transistors.CHAPTER 1 Introduction 1 1.1 Background 1 1.2 Substrate for Epitaxial Growth of GaN 6 1.3 Research Aims and Objectives 8 1.4 Organization of Thesis 9 1.5 References 11 CHAPTER 2 Technology Development and Fabrication of AlGaN/GaN HEMTs on Si substrate 15 2.1 Introduction 15 2.2 Epitaxy Layer Structure 16 2.3 Device Fabrication Processes 17 2.3.1 Sample Preparation 18 2.3.2 Mesa Isolation 19 2.3.3 Ohmic Formation 20 2.3.4 Schottky Contacts 24 2.3.5 Contac Pads 26 2.3.6 Air-bridge Interconnection 26 2.4 References 33 CHAPTER 3 Au-Plated Through-Wafer Vias for AlGaN/GaN HEMTs on Si substrate 36 3.1 Introduction 36 3.2 Via-hole Fabrication 37 3.2.1 Experiments 38 3.2.2 Tapered Source Via Formation 40 3.2.3 GaN Etching Process 50 3.2.4 Au Electroplating 53 3.3 Back-side Process Flows 54 3.3.1 Individual Source Via 58 3.3.2 Au-Sn Eutectic Solder Die Attach 60 3.3.3 Thermal Resistance Measurement 61 3.4 References 66 CHAPTER 4 AlGaN/GaN HEMTs for RF applications 69 4.1 Introduction 69 4.2 Advantages of AlGaN/GaN HEMTs for RF Power Devices 70 4.3 RF Performance Limitations 73 4.3.1 Surface States 73 4.3.2 Current Collapse Phenomenon 75 4.4 Device Fabrication 79 4.4.1 Device Layout 85 4.4.2 Slant Gate Process 86 4.4.3 Fluorine Plasma Treatment process 89 4.5 Device Characterization 93 4.5.1 DC and Small Signal Performance 93 4.5.2 Pulse Characteristics 98 4.5.3 Large Signal Performance 99 4.6 Wide Periphery Devices 103 4.6.1 Large Signal Performance 104 4.7 Summary 109 4.8 Reference 110 CHAPTER 5 AlGaN/GaN HEMTs for Power applications 115 5.1 Introduction 115 5.2 Advantages of AlGaN/GaN HEMTs for Power Switching Devices 116 5.2.1 Enhancement-mode Operation 117 5.2.2 High Breakdown Voltage 119 5.3 Device Fabrication 121 5.3.1 Gate Recess Process 124 5.3.2 Plasma Enhance ALD SiNx Film 138 5.4 Characterization for Normally-off GaN Transistors 140 5.4.1 DC Characteristics 140 5.4.2 Breakdown Voltage Characteristics 144 5.4.3 Dynamic Ron Characteristics 146 5.5 Summary 148 5.6 Reference 149 CHAPTER 6 Conclusions and Future Works 155 6.1 Conclusions and Future Works 155 Appendix 159 Abstract in Korean 169 Research Achievements 174Docto

An investigation of nanoscale materials and their incorporation in patch antenna for high frequency applications

The rapid development in the polymer-based electronic contribute a strong determination for using these materials as substitute to the high-cost materials commonly used as medium substrate in the fabrication of Microstrip Patch Antenna (MPA). Antenna technology can strongly gain from the utilisation of low-cost, flexible, light weight with suitable fabrication techniques. The uniqueness of this work is the use of variety of common but unexplored different polymer materials such as Polyethylene (PE), Polypropylene (PP), Polyvinyl chloride, (PVC) Polystyrene (PS), Polystyrene fibre (PSF) as the substrates for the design and fabrication of different MPAs for communication and sensing applications in millimetre wave (MMW)region. Electrospinning (ES) technique is used to reconstruct PS and produced PSF material of low dielectric constant. A co-solvent vehicle(comprising 50:50 ratio) of Dichloromethane (DCM) and acetone was utilised with processing condition of solution infusion flow-rate of 60μL/min and an applied voltage of 12± kV yielded rigid PSF substrates. The PSF Produced has complex permittivity of 1.36±5% and a loss tangent of 2.4E-04±4.8E-04 which was measured using Spilt-Post Dielectric Resonators (SPDR) technique at National Physics Laboratory, Teddington, London. A diamond-shaped MPAs on RT Duriod material were simulated and fabricated using photo-lithography for different inner lengths to work in the frequencies range from (1-10 GHz). The resonant frequency is approximated as a function of inner length L1 in the form of a polynomial equation. The fabricated diamond-shaped MPA more compact (physical geometry) as compared with a traditional monopole antenna. This MPAs experimentally measured and have a good agreement with the simulated results. The coplanar waveguide (CPW) diamond-shaped MPA working in the MMW region was designed and fabricated with polymer materials as substrates using thermal evaporation technique and the RF measurement was carried out using Vector Network Analyser (VNA). The resonant frequencies of the CPW diamond shaped MPAs for (PE, PP, PVC, PS and PSF) were found to be 67.5 GHz, 72.36 GHz, 62.41 GHz, 63.25 GHz and 80.58 GHz, respectively. The antenna fabricated on PSF were resonating at higher frequency when compared to the other polymers materials. In adding an air-bridge to the CPW diamond-shaped MPA the resonating frequency increased from ≈55 GHz to≈ 62 GHz. Three different shaped nano-patch antennas (Diamond shaped, diamond shaped array and T-shaped) have been designed, simulated and fabricated on Silicon substrate with DLC deposition using focused Ion Beam (FIB) technique, these antennas were found to resonate at 1.42 THz with (-19 dB return loss), 2.42 THz with (-14 dB return loss) and 1.3 THz with (-45 dB return loss) respectively

Micro/Nano Structures and Systems

Micro/Nano Structures and Systems: Analysis, Design, Manufacturing, and Reliability is a comprehensive guide that explores the various aspects of micro- and nanostructures and systems. From analysis and design to manufacturing and reliability, this reprint provides a thorough understanding of the latest methods and techniques used in the field. With an emphasis on modern computational and analytical methods and their integration with experimental techniques, this reprint is an invaluable resource for researchers and engineers working in the field of micro- and nanosystems, including micromachines, additive manufacturing at the microscale, micro/nano-electromechanical systems, and more. Written by leading experts in the field, this reprint offers a complete understanding of the physical and mechanical behavior of micro- and nanostructures, making it an essential reference for professionals in this field

Wide Bandgap Based Devices: Design, Fabrication and Applications, Volume II

Wide bandgap (WBG) semiconductors are becoming a key enabling technology for several strategic fields, including power electronics, illumination, and sensors. This reprint collects the 23 papers covering the full spectrum of the above applications and providing contributions from the on-going research at different levels, from materials to devices and from circuits to systems