The authors have found that patterning polyimide coatings containing organosilane adhesion promoter using pure oxygen plasma resulted in a thin silicon-rich residue layer. They show in this paper that adding small amounts of fluorine-containing gas to the etching gas mixture is necessary in order to achieve residue-free polyimide plasma etching. They report residue-free plasma etching of polyimide coatings with both isotropic and anisotropic profiles, using either metal or oxide hard masks. These etching methods are however not sufficient for the fabrication of high density metal filled vias in 10 lm thick polyimide coatings. In order to improve the metal step coverage over the vias while keeping the pitch as small as possible, the authors have developed a two-step etching recipe combining both isotropic and anisotropic profiles, resulting in wine-glass shaped vias.
The flex-to-rigid (F2R) platform allows for the fabrication of miniature and flexible sensor assemblies for minimally invasive medical instruments such as catheters and guidewires. Devices fabricated on silicon wafers are transferred onto polyimide and partially rendered flexible by means of a two-step backside silicon deep reactive ion etching. The flexibility allows for the devices to be folded into, or wrapped around the tip of the instruments. The fabrication of the whole assembly is based on standard integrated circuit manufacturing technologies so that it is possible to scale the devices down to the dimension of the smallest guidewires. Several demonstrations are presented to show the versatility of the F2R technology, and a polyimidebased flexible thermal flow sensor for application at the tip of a 360-µm diameter guidewire is introduced.
The world's first flexible ultra-thin-body SOI single-photon avalanche diode (SPAD) is reported with peak photon detection probability (PDP) at 11%, dark count rate (DCR) around 20kHz and negligible afterpulsing and cross-talk. It compares favorably with CMOS SPADs while it can be bended to 10mm-diameter and operate both in frontside-(FSI) and backside-illumination (BSI).
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