Vertical Alignment of Nematic Liquid Crystals Based on Spontaneous Alignment Layer Formation between Silver Nanowire Networks and Nonionic Amphiphiles

The vertical arrangement of nematic liquid crystals (LCs) in displays can be generally achieved by introducing a polyimide material onto indium tin oxide electrodes. However, this method requires multiple coating and deposition processes as well as high curing temperature, restricting the potential applicability to flexible displays. Thus, we herein propose the facile approach for homeotropic alignment of nematic LCs based on spontaneous alignment layer formation between silver nanowire networks and nonionic amphiphiles. The silver nanowires as transparent electrode materials were spin-coated on glass substrate and 4-(4-heptylphenyl)benzoic acids as nonionic amphiphiles were doped into the LC medium. The nonionic amphiphiles were spontaneously bonded to the polyvinylpyrrolidone capping layer of silver nanowire networks through polar interactions, creating the self-assembled alignment layer of nonionic amphiphiles on silver nanowire electrodes. In addition, the alkyl chains of the amphiphiles interacted with the LC molecules, leading to stable directional LC alignment along vertical direction. The electro-optical characteristics of the manufactured LC cell were comparable to those of conventional device including polyimide layer and indium tin oxide electrode. Overall, the combination of silver nanowire electrode and nonionic amphiphiles presents a new way to achieve the vertical alignment of nematic LCs without polyimide layer.

Wirebond Process Improvement through Silicon Die Polyimide Removal

This study aims to develop polyimide etching process on the silicon die after decapsulation to resolve the wire shear issue during ball shear data gatherings. The shear strength of the ball is affected by the presence of polyimide insulator during ball shearing process, due to the polyimide layer of the silicon die being coplanar with the ball height of the wire. Experimentation and statistical analysis were done on units with and without polyimide coating, with Sodium Hydroxide (NaOH) used to remove the excess polyimide. Results revealed that silicon dice without polyimide coating resulted to better reading in terms of ball shear.

Simulation of cavitation effects in blister-assisted laser-induced forward transfer of fluids

In Blister-Actuated Laser-Induced Forward Transfer (BA-LIFT), a laser pulse generates a blister in an intermediate polyimide layer to push away the fluid. In this work, a Phase Field model has been proposed to study the transference mechanisms. Simulations and experimental shadowgraphy images for BA-LIFT of water-glycerol mixtures have been compared. The transference mechanism in BA-LIFT is ideally only mechanical and does not explain some secondary effects in the jet expansion that have already been described in other LIFT techniques and associated with the cavitation of a thermally generated vapor bubble.The numerical model can reproduce the expansion of the main jet. The addition of a second push at 9 μs delay allows reproducing the secondary effects. Four possible causes of the second push have been studied: absorption of the laser pulse in the fluid, thermal conduction through the polyimide layer, a mechanical rebound of the elastically deformed blister, or pressure fall due to fluid velocity. After the analysis, the first three explanations have been rejected, and a hypothesis is proposed: the velocity field generated by the blister produces a cavitation bubble in the interface between the polyimide layer and the fluid, whose effects would be the same than the cavitation of the vapor bubble in other LIFT techniques.

Multi-functional Smart Skin for Multi-dimensional Perception for Humanoid Robots

Previously reported artificial smart skins for humanoid robots suffer difficulties in achieving multi-dimensional sensing in a simple structure with a low system cost. In this paper, we exhibit a polyimide/copper/PVDF structured smart skin for multidimensional sensing (including position, proximity, force and humidity), which is enabled by smart utilization of dielectric property of polyimide layer and piezoelectric of the PVDF layer. Experimental results demonstrate that the developed technique successfully obtains large area, flexibility, and multiple-function with simple device structure and low component cost, potentially enabling massive production and advanced services for the humanoid robots’ applications.

Multi-functional Smart Skin for Multi-dimensional Perception for Humanoid Robots

Previously reported artificial smart skins for humanoid robots suffer difficulties in achieving multi-dimensional sensing in a simple structure with a low system cost. In this paper, we exhibit a polyimide/copper/PVDF structured smart skin for multidimensional sensing (including position, proximity, force and humidity), which is enabled by smart utilization of dielectric property of polyimide layer and piezoelectric of the PVDF layer. Experimental results demonstrate that the developed technique successfully obtains large area, flexibility, and multiple-function with simple device structure and low component cost, potentially enabling massive production and advanced services for the humanoid robots’ applications.

Silicone-based Chip-in-Foil System

Aiming at devices for bioelectronic medicine, this paper proposes a die embedding process for the fabrication of flexible smart implants. By combining thinned bare dies with a polymeric encapsulation, completely flexible implants can be designed. The dies are encapsulated using a flip-chip process and a backfilling with silicone rubber. A completely even surface without detectable edge between the chip and the surrounding polymer substrate is achieved by gluing the chips face-down onto a polyimide-covered substrate. The backside is coated with silicone rubber and a second carrier substrate is attached. Removing the first substrate subsequent to curing of the silicone leads to chips located under a continuous polyimide layer, enabling the use of microtechnology for further processing steps. A custom-made test chip is proposed that enables the evaluation of the mechanical and chemical stability of the system.

Dark Current Leakage in Optoelectronic Hermetic Packages

In this work, the root cause of the increase in dark current occurring over time at high temperature in hermetic packages, such as those used in optoelectronic devices, was investigated. It was observed that hermetic Receiver Optical Subassembly (ROSA) devices show continuously increasing dark current when stressed and monitored at 85°C over an extended period of time, reaching, in some cases, values greater than 500nA. However, this increase in leakage current was recoverable once the package seal is broken, and this behavior was found to be very repeatable. Photodetectors from two different suppliers were tested and found to have dark current which is dependent on the fabrication process, as the photodetector (PD) from supplier 1 (PD1) showed three times higher leakage than the photodetector from supplier 2 (PD2). The main difference between the two photodetectors is that the polyimide layer in PD1 in significantly greater than in PD2. It was also observed that 48 hour pre-seal baking at 120°C keeps the dark current constant at much lower levels, but does not stop it completely from rising over time.