Manufacture of Ni-Co thin films for flexible electronics

An article published in the journal Sensors and actuators: A. Physics explores nickel and cobalt (Ni-Co) alloys as a new material for versatile substrates of foldable micro-gadgets.

Study: Characterization of Ni-Co thin films and their applications to multifunctional substrates of flexible microdevices. Image Credit: KPixMining / Shutterstock.com

During the manufacturing process, thin films of Ni-Co were produced on a silicon carrier wafer using traditional methods of electroplating and micromachining, and then removed from the carrier wafer using ‘a unique release mechanism suggested in this study.

Flexible electronic devices

Flexible electronic equipment, such as monitors, radio frequency identifiers (RFID), portable gadgets, energy harvesting gadgets, and micro-electromechanical sensors (MEMS), have recently been produced for various applications.

Flexible electronic components are thinner, lighter, and less likely to break than traditional electronic equipment built on substrates of hard silicon or glass. With such characteristics, it is expected that the need for flexible gadgets would skyrocket, making flexible substrate materials essential.

Ultra-thin metal foils, polymers and glasses are often used as flexible substrate materials. Metal foil substrates outperform polymeric substrates in high temperature stability and mechanical strength; they also outperform ultra-thin glass and silicon substrates in terms of shock absorption.

Due to these properties, metal foils could have potential applications as substrate materials for flexible micro-gadgets.

Three ways of creating flexible microdevices on thin metallic films can be adopted: the roll-to-roll approach, producing the microdevices directly on thin metallic substrates, or connecting the thin metallic film to a carrier wafer.

Metals offer strong electrical properties, excellent high temperature stability and mechanical durability, which allows them to be used as substrates and sensory elements or structural components for flexible MEMS systems.

Accordingly, thin metal films shaped into a particular shape can be used as versatile substrates, such as a structural substrate or a sensory substrate.

Research methodology

As a new material for making versatile substrates of flexible micro-gadgets, an alloy of nickel and cobalt (Ni-Co) has been investigated.

Electroplating was used to produce thin films of Ni-Co on a Si carrier wafer, which were then shaped into exact shapes using a standard micromachining procedure.

The films were then removed from the backing wafer using the new release technique. The researchers were able to create a thin foldable Ni-Co film with complex shapes using the proposed production method.

The chemical composition, surface finish, cross-sectional morphologies, and electrical, thermal and mechanical characteristics of Ni-Co films were investigated using several evaluation techniques for their classification.

Main conclusions

In this study, the electrical, mechanical and thermal characteristics of the Ni-Co alloy (Ni3Co) have been tested for application as a versatile substrate for use in flexible micro-gadgets.

Ni-Co thin sheet has been determined to be suitable as a structural substrate for flexible micro-gadgets due to its remarkable toughness, Young’s modulus, yield strength and ultimate tensile strength. In addition, Young’s modulus, yield strength and ultimate tensile strength of Ni-Co thin sheet were found to be 1.7x, 7.0x and 5.2x respectively higher than those of steel. stainless.

The surface roughness of the Ni-Co foil was minimal, suggesting that it exhibits a mirror-like surface finish.

Regarding thermal characteristics, the specific heat capacity of Ni-Co thin sheet was almost half of the specific heat capacity of stainless steel. In addition, the Ni-Co thin sheet has a thermal diffusivity which is about 6.2 times higher than the thermal diffusivity of stainless steel.

In view of its remarkable mechanical strength, higher thermal diffusivity, reduced specific heat, Ni-Co thin foil has been found useful as a structural substrate for electrothermal actuation requiring good tensile properties and thermal reaction. frequency to heat.

New applications

A thin layer of Ni-Co alloy can be deposited on a sensory substrate, which acts as both a sensor and a substrate.

Using Ni-Co substrate designed with meander-type strain gauge as the pulse sensor, the pulse could be measured accurately by sticking it to the left wrist using ordinary tape.

Its connection to a digital joint made it possible to use the same Ni-Co sensory substrate as a digital joint sensor. The movement of the seal was followed by monitoring the output voltage of a quarter bridge circuit that included the sensing substrate.

The output voltage varied in response to finger movement, indicating that the Ni-Co thin film is sensitive enough to be used as a sensory substrate.

Continue reading: Enhance epoxy resin with flower-like nanoparticles.

Reference

Kim, Y., & Kim, K.-S. (2021) Characterization of Ni-Co thin film and its applications to multifunctional substrates of flexible microdevices. Sensors and actuators: A. Physics. Available at: https://www.sciencedirect.com/science/article/pii/S0924424721007585?via%3Dihub

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