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

Conference of Microelectronic Research 1997

https://scholarworks.rit.edu/meec_archive/1006/thumbnail.jp

Driving microfluidic flows with three dimensional electrodes.

Most of the structures in submillimeter-scale engineering are created from thin films, making them essentially two-dimensional (2D). Significant work has been done to fabricate 3D structures using self-folding, a deterministic form of self-assembly, and three dimensional lithographic and non-lithographic patterning. The objective of this work is to propose different fabrication and patterning strategies of 3D structures used as pumping electrodes for micro fluidic applications. 3D electrodes drive flows over the whole channel height while 2D electrodes stay near one wall. The first application of the 3D electrodes is mixing chemical or biological samples with reagents for chemical analysis which is one of the most time consuming operations in microfluidic platforms. The mixer used is based on the electrokinetic phenomenon of induced charge electro-osmosis (ICEO). ICEO creates microvortices around polarized posts with gold coated sidewalls, connected to embedded electrodes, by application of alternating current (AC) electric fields. These microvortices around posts help in mixing the two reagents very quickly. These vertical sidewall gold coated posts and embedded electrodes are fabricated using 3D photolithographic patterning and an ion milling fabrication technique. The second application is fast ac electro-osmotic (ACEO) pumps using 3D electrodes. These 3D electrodes dramatically improve the flow rate and frequency range of ACEO pumps over the planar electrodes. A non-photolithographic electrode patterning method is proposed to fabricate such electrodes. The method is based on shadowed evaporation of metal on an insulating substrate. This method is considered to be simple and cost effective compared to others used to create these stepped 3D electrodes. Finally, a self-folding technique is proposed to create out-of plane three dimensional electrodes for ACEO tube pumps. The technique depends on the strain mismatch between two different layered sheets of material. One layer usually has compressive stress, i.e. thermally grown Si02, and the other has relatively tensile stress, i.e. metals. The design is similar to the planar electrodes design in the literature, except as a 3D electrode it interacts with a larger volume of fluid for a more efficient pump

PCB Quality Metrics that Drive Reliability (PD 18)

Risk based technology infusion is a deliberate and systematic process which defines the analysis and communication methodology by which new technology is applied and integrated into existing and new designs, identifies technology development needs based on trends analysis and facilitates the identification of shortfalls against performance objectives. This presentation at IPC Works Asia Aerospace 2019 Events provides the audience a snapshot of quality variations in printed wiring board quality, as assessed, using experiences in processing and risk analysis of PWB structural integrity coupons. The presentation will focus on printed wiring board quality metrics used, the relative type and number of non-conformances observed and trend analysis using statistical methods. Trend analysis shows the top five non-conformances observed across PWB suppliers, the root cause(s) behind these non-conformance and suggestions of mitigation plans. The trends will then be matched with the current state of the PWB supplier base and its challenges and opportunities. The presentation further discusses the risk based SMA approaches and methods being applied at GSFC for evaluating candidate printed wiring board technologies which promote the adoption of higher throughput and faster processing technology for GSFC missions