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

Fabrication of Silicon Microneedles for Dermal Interstitial Fluid Extraction in Human Subjects

The goal of this project is to design and develop a fabrication process for silicon microneedle arrays to extract dermal interstitial fluid (ISF) from human skin. ISF is a cell- free, living tissue medium that is known to contain many of the same, clinical biomarkers of general health, stress response and immune status as in blood. However, a significant barrier to adoption of ISF as a diagnostic matrix is the lack of a rapid, minimally invasive method of access and collection for analysis. Microfabricated chips containing arrays of microneedles that can rapidly and painlessly access and collect dermal ISF for bioassay could greatly facilitate point-of-care diagnosis and health monitoring, especially in times of crisis or in austere environments, where drawing venous blood poses an unnecessary infection or biohazard risk. Two different fabrication methods were explored. The first method borrows from a previously reported dicing saw process, where a series of parallel and perpendicular cuts of partial depth are made into a thicker silicon wafer, creating arrays of square columns, which are subsequently sharpened into needles. The second method uses a new, entirely-DRIE process to create the arrays of columns. The columns are sharpened into needles using an isotropic wet etch method (HNA etch) which preferentially enhances etching at the tips and diminishes etching at the base, creating remarkably sharp, conical shaped needles capable of piercing skin. The needles contain holes that pass through the wafer to the opposite side, where they connect to a series of microfluidic channels that lead to a reservoir. The back of the wafer is bonded to glass, providing a hydrophilic cap to the channels, as well as a way to see into the device to detect whether the channels are filling with liquid. The fabrication procedures for both methods are presented, along with 2D- and 3D-rendered schematics for the final devices. Needle geometric shape is crucial to their ability to extract ISF. To determine the appropriate pre-sharpened etched shape, needle columns with a variety of different shapes were designed, produced, sharpened, and examined under a scanning electron microscope. The most promising shapes were selected for further processing and testing. Resulting chips were first bench tested to ensure capillary filling capability, and then tested for ISF collection from human skin. Microneedle arrays which were successfully demonstrated to extract ISF are presented, and the unsuccessful shapes are also shown in the interest of completion. Potential means for improving performance and future research directions are discussed

Recent Progress on 3D Silicon Detectors

3D silicon detectors, in which the electrodes penetrate the sensor bulk perpendicular to the surface, have recently undergone a rapid development from R\&D over industrialisation to their first installation in a real high-energy-physics experiment. Since June 2015, the ATLAS Insertable B-Layer is taking first collision data with 3D pixel detectors. At the same time, preparations are advancing to install 3D pixel detectors in forward trackers such as the ATLAS Forward Proton detector or the CMS-TOTEM Proton Precision Spectrometer. For those experiments, the main requirements are a slim edge and the ability to cope with non-uniform irradiation. Both have been shown to be fulfilled by 3D pixel detectors. For the High-Luminosity LHC pixel upgrades of the major experiments, 3D detectors are promising candidates for the innermost pixel layers to cope with harsh radiation environments up to fluences of $2\times10^{16}$\,n$_{eq}$/cm$^2$ thanks to their excellent radiation hardness at low operational voltages and power dissipation as well as moderate temperatures. This paper will give an overview on the recent developments of 3D detectors related to the projects mentioned above and the future plans.Comment: Proceedings of the 24th International Workshop on Vertex Detectors, 1-5 June 2015, Santa Fe, US

Doctor of Philosophy

dissertationPrecise optical neural stimulation is an essential element in the use of optogenetics to elicit predictable neural action potentials within the brain, but accessing specific neocortical layers, light scattering, columniation, and ease of tissue damage pose unique challenges to the device engineer. This dissertation presents the design, simulation, microfabrication, and characterization of the Utah Optrode Array (UOA) for precise neural tissue targeting through three main objectives: 1. Maskless wafer-level microfabrication of optical penetrating neural arrays out of soda- lime glass: Utah Optrode Array. 2. Utah Optrode Array customization using stereotactic brain atlases and 3D CAD modeling for optogenetic neocortical interrogation in small rodents and nonhuman primates. 3. Single optrode characterization of the UOA for neocortical illumination. Maskless microfabrication techniques were used to create 169 individual 9 × 9 arrays 3.85 mm × 3.85 mm with 1.1 mm long optrodes from a single two inch glass wafer. The 9 × 9 UOA was too large for precise targeting of the upper layers of the cortex in smaller animals such as mice, so an array customization method was developed using Solidworks and off-the-shelf brain atlases to create 8 × 6 arrays 3.45 mm × 2.45 mm with 400 μm long optrodes. Stereotactic atlases were imported into Solidworks, splined, and lofted together to create a single 3D CAD model of a specific region of interest in the brain. Chronic and acute brain trauma showed excellent results for the 8 × 6 arrays in C57BL/6 wild-type mice (Mus musculus) and macaque monkey (Macaca fascicularis). Simulation, characterization, and radiometric testing of a single optrode of the 9 × 9 array was necessary to prove the ability to transmit light directly to specific tissue. Zemax optical design software was used to predict the light transmission capabilities, and then these results were compared to actual bench-top results. Insertion loss was both predicted and measured to be 3.7 dB. Power budgeting showed 9% of the light was lost at the interfaces of the UOA's backplane and tip in air, and 48% was lost through back-scattering, leaving 43% transmitting through the optrode with no measurable taper loss. Scanning electron microscopy showed small amounts of devitrification of the glass, and atomic force microscopy showed average surface roughness to be 13.5 nm and a root mean square roughness of 20.6 nm. The output beam was profiled in fluorescein dye with a total divergence angle of 63◦ with a cross over distance to adjacent beams at 255 μm

Mems (Micro-Electro-Mechanical-Systems) Based Microfluidic Platforms for Magnetic Cell Separation

Microfluidic platforms for magnetic cell separation were developed and investigated for isolation of magnetic particles and magnetically tagged cells from a fluidic sample. Two types of magnetic separation platforms were considered: an Isodynamic Open Gradient Magnetic Sorter (OGMS) and a multistage bio-ferrograph. Miniaturized magnets were designed using magnetostatic simulation software, microfluidic channels were fabricated using microfabrication technology and magnetic separation was investigated using video microscopy and digital image processing. The isodynamic OGMS consisted of an external magnetic circuit and a microfabricated channel (biochip) with embedded magnetic elements. The biochip is placed inside the magnetic field of the external circuit to obtain nearly constant energy density gradient in the portion of the channel used for separation. The microfabrication process involved improving adhesion of thick SU-8 to Pyrex, forming enclosed channels using a low temperature SU-8 adhesive bonding, and fabricating patterned plating molds on both sides of the bonded wafers. Adhesion of SU-8 to Pyrex was improved by using a highly crosslinked thin SU-8 adhesion layer, and enclosed microchannels were fabricated using selectively exposed SU-8 bond formation layers. Electroplating molds were fabricated using KMPR photoresists and were integrated on both sides of the bonded wafers. The multistage bio-ferrograph consisted of a microfabricated enclosed channel placed on the surface of a multi-unit magnet (4 trapezoidal magnets placed in series) assembly such that magnetic cells from a flowing stream would be deposited on designated locations. The OGMS was able to deflect magnetic particles by 500-1000 microns and the capture efficiencies of magnetic particles and cells with the multistage bio-ferrograph were 80-85 percent and 99.5 percent, respectivel

Mems (Micro-Electro-Mechanical-Systems) Based Microfluidic Platforms for Magnetic Cell Separation

Microfluidic platforms for magnetic cell separation were developed and investigated for isolation of magnetic particles and magnetically tagged cells from a fluidic sample. Two types of magnetic separation platforms were considered: an Isodynamic Open Gradient Magnetic Sorter (OGMS) and a multistage bio-ferrograph. Miniaturized magnets were designed using magnetostatic simulation software, microfluidic channels were fabricated using microfabrication technology and magnetic separation was investigated using video microscopy and digital image processing. The isodynamic OGMS consisted of an external magnetic circuit and a microfabricated channel (biochip) with embedded magnetic elements. The biochip is placed inside the magnetic field of the external circuit to obtain nearly constant energy density gradient in the portion of the channel used for separation. The microfabrication process involved improving adhesion of thick SU-8 to Pyrex, forming enclosed channels using a low temperature SU-8 adhesive bonding, and fabricating patterned plating molds on both sides of the bonded wafers. Adhesion of SU-8 to Pyrex was improved by using a highly crosslinked thin SU-8 adhesion layer, and enclosed microchannels were fabricated using selectively exposed SU-8 bond formation layers. Electroplating molds were fabricated using KMPR photoresists and were integrated on both sides of the bonded wafers. The multistage bio-ferrograph consisted of a microfabricated enclosed channel placed on the surface of a multi-unit magnet (4 trapezoidal magnets placed in series) assembly such that magnetic cells from a flowing stream would be deposited on designated locations. The OGMS was able to deflect magnetic particles by 500-1000 microns and the capture efficiencies of magnetic particles and cells with the multistage bio-ferrograph were 80-85 percent and 99.5 percent, respectivel

Power system applications of fiber optic sensors

This document is a progress report of work done in 1985 on the Communications and Control for Electric Power Systems Project at the Jet Propulsion Laboratory. These topics are covered: Electric Field Measurement, Fiber Optic Temperature Sensing, and Optical Power transfer. Work was done on the measurement of ac and dc electric fields. A prototype sensor for measuring alternating fields was made using a very simple electroscope approach. An electronic field mill sensor for dc fields was made using a fiber optic readout, so that the entire probe could be operated isolated from ground. There are several instances in which more precise knowledge of the temperature of electrical power apparatus would be useful. This report describes a number of methods whereby the distributed temperature profile can be obtained using a fiber optic sensor. The ability to energize electronics by means of an optical fiber has the advantage that electrical isolation is maintained at low cost. In order to accomplish this, it is necessary to convert the light energy into electrical form by means of photovoltaic cells. JPL has developed an array of PV cells in gallium arsenide specifically for this purpose. This work is described

Reliability analysis of foil substrate based integration of silicon chips

Flexible electronics has attracted significant attention in the recent past due to the booming wearables market in addition to the ever-increasing interest for faster, thinner and foldable mobile phones. Ultra-thin bare silicon ICs fabricated by thinning down standard ICs to thickness below 50 μm are flexible and therefore they can be integrated on or in polymer foils to create flexible hybrid electronic (FHE) components that could be used to replace rigid standard surface mount device (SMD) components. The fabricated FHE components referred as chip foil packages (CFPs) in this work are ideal candidates for FHE system integration owing to their ability to deliver high performance at low power consumption while being mechanically flexible. However, very limited information is available in the literature regarding the reliability of CFPs under static and dynamic bending. The lack of such vital information is a major obstacle impeding their commercialization. With the aim of addressing this issue, this thesis investigates the static and dynamic bending reliability of CFPs. In this scope, the static bending reliability of CFPs has been investigated in this thesis using flexural bending tests by measuring their fracture strength. Then, Finite Element Method (FEM) simulations have been implemented to calculate the fracture stress of ultra-thin flexible silicon chips where analytical formulas may not be applied. After calculating the fracture stress from FEM simulations, the enhancement in robustness of ultra-thin chips (UTCs) against external load has also been proved and quantified with further experimental investigations. Besides, FEM simulations have also been used to analyse the effect of Young’s Modulus of embedding materials on the robustness of the embedded UTCs. Furthermore, embedding the UTCs in polymer layers has also been experimentally proven to be an effective solution to reduce the influence of thinning and dicing induced damages on the robustness of the embedded UTCs. Traditional interconnection techniques such as wire bonding may not be implemented to interconnect ultra-thin silicon ICs owing to the high mechanical forces involved in the processes that would crack the chips. Therefore, two novel interconnection methods namely (i) flip-chip bonding with Anisotropic Conductive Adhesive (ACA) and (ii) face-up direct metal interconnection have been implemented in this thesis to interconnect ultra-thin silicon ICs to the corresponding interposer patterns on foil substrates. The CFP samples thus fabricated were then used for the dynamic bending reliability investigations. A custom-built test equipment was developed to facilitate the dynamic bending reliability investigations of CFPs. Experimental investigations revealed that the failure of CFPs under dynamic bending was caused mainly by the cracking of the redistribution layer (RDL) interconnecting the chip and the foil. Furthermore, it has also been shown that the CFPs are more vulnerable to repeated compressive bending than to repeated tensile bending. Then, the influence of dimensional factors such as the thickness of the chip as well as the RDL on the dynamic bending reliability of CFPs have also been studied. Upon identifying the plausible cause behind the cracking of the RDL leading to the failure of the CFPs, two methods to improve the dynamic bending reliability of the RDL have been suggested and demonstrated with experimental investigations. The experimental investigations presented in this thesis adds some essential information to the state-of-the-art concerning the static and the dynamic bending reliability of UTCs integrated in polymer foils that are not yet available in the literature and aids to establish in-depth knowledge of mechanical reliability of the components required for manufacturing future FHE systems. The strategies devised to enhance the robustness of UTCs and CFPs could serve as guidelines for fabricating reliable FHE components and systems

Characterization of a CMUT Array

Ultrasound transducers are used in a broad range of applications covering from underwater communications to medical imaging and treatment. The ultrasonic transducer determines the key specifications such as resolution, sensitivity and signal to noise ratio. The capacitive micromachined ultrasonic transducer (CMUT) has emerged as an alternative to standard piezoelectric transducers due to advanced microelectronics fabrication technology and methods. Comparing to piezoelectric transducers, the CMUT is superior to it\u27s competitor with higher acoustic bandwidth, higher sensitivity and greater coupling with the acoustic medium. Design, fabrication, and characterization of a capacitive micromachined ultrasonic transducer (CMUT) array have been presented along this thesis. The array is designed to operate in the frequency range of 113-167 kHz. The CMUT array is fabricated using an SOI based fabrication technology and includes 6x6 CMUTs. Necessary test setups and readout circuitry is designed in order to carry out the characterization process. Static analysis results are verified with Wyko optical profilometer, Agilent LCR meter and SEM analysis. Dynamic characterizations are done with Polytec MSA-4 laser Doppler vibrometer. An efficient and low noise capacitive readout circuit is designed using transimpedance amplifier scheme with 75 kilo ohm gain and fabricated on a PCB. The developed analytical models, FEA and experimental results are in very good agreement to exhibit accuracy of the design methodology