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Fabrication of Ni-Co Thin Films for Flexible Electronics

A paper published in the journal Sensors and Actuators: A. Physical explores alloys of nickel and cobalt (Ni–Co) as a novel material for multipurpose substrates of pliable micro-gadgets.

flexible electronics, Ni-Co thin films

Study: Characterization of Ni–Co Thin Film and Its Applications to Multifunctional Substrates of Flexible Microdevice. Image Credit: KPixMining/Shutterstock.com

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

Flexible Electronic Devices

Flexible electronic equipment, like monitors, radio-frequency identifiers (RFID), wearable gadgets, energy recovery gadgets, and micro-electromechanical sensors (MEMS), have recently been produced for various applications.

Flexible electronics are slimmer, lightweight, and less likely to fracture than traditional electronic equipment built on hard silicon or glass substrates. With such features, it is projected that the need for flexible gadgets would skyrocket, making flexible substrate materials essential.

Metal foils, polymers, and ultra-thin glasses are often employed as flexible substrate materials. Metallic foil substrates outperform polymeric substrates in terms of stability at elevated temperatures and mechanical strength; they also outperform ultra-thin glass and silicon substrates in terms of impact absorption.

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

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

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

As a result, thin metallic films shaped into a particular form may be utilized as multipurpose substrates, such as a structural substrate or a sensory substrate.

Research Methodology

As a novel material for making multipurpose substrates of flexible micro-gadgets, an alloy of nickel and cobalt (Ni–Co) was investigated.

Electrodeposition was used to produce thin Ni–Co films on a Si carrier wafer, which were then shaped into exact forms using a standard micromachining procedure.

The films were then removed from the carrying wafer using the novel release technique. Researchers were able to create a Ni–Co pliable thin layer with complex forms using the proposed production method.

The chemical makeup, surface finish, cross-sectional morphologies, and electric, thermal, and mechanical characteristics of the Ni-Co films were studied utilizing several assessment techniques for their classification.

Key Findings

In this study, the electrical, mechanical, and thermal characteristics of the Ni–Co alloy (Ni3Co) were examined for application as a multipurpose substrate for use in flexible micro-gadgets.

It was determined that the Ni–Co thin sheet is adequate as a structural substrate for flexible micro-gadgets owing to its remarkable toughness, young’s modulus, yield stress, and ultimate tensile strength. Furthemore, the Young's modulus, yield stress, and ultimate tensile strength of the Ni–Co thin sheet were found to be 1.7x, 7.0x, and 5.2x greater than that of stainless steel, respectively.

The Ni–Co thin sheet's surface roughness was minimal, suggesting that it exhibits a mirror-like surface finish. 

As for thermal characteristics, the specific heat capacity of the Ni–Co thin sheet was almost half the specific heat capacity of stainless steel. Furthermore, the Ni–Co thin sheet has a thermal diffusivity which is roughly 6.2 times greater than the thermal diffusivity of stainless steel.

Given its remarkable mechanical strength, higher thermal diffusivity, reduced specific heat, Ni–Co thin sheet was determined to be useful as a structural substrate for electro-thermal actuation requiring good tensile properties and frequency reaction to heat.

Novel Applications

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

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

Connecting it to a finger joint enabled the same Ni-Co sensory substrate to be employed as a finger-joint sensor. The movement of the joint was tracked by monitoring the voltage output of a quarter-bridge circuit that included the sensing substrate.

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

Continue reading: Improving 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. Physical. Available at: https://www.sciencedirect.com/science/article/pii/S0924424721007585?via%3Dihub

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Shaheer Rehan

Written by

Shaheer Rehan

Shaheer is a graduate of Aerospace Engineering from the Institute of Space Technology, Islamabad. He has carried out research on a wide range of subjects including Aerospace Instruments and Sensors, Computational Dynamics, Aerospace Structures and Materials, Optimization Techniques, Robotics, and Clean Energy. He has been working as a freelance consultant in Aerospace Engineering for the past year. Technical Writing has always been a strong suit of Shaheer's. He has excelled at whatever he has attempted, from winning accolades on the international stage in match competitions to winning local writing competitions. Shaheer loves cars. From following Formula 1 and reading up on automotive journalism to racing in go-karts himself, his life revolves around cars. He is passionate about his sports and makes sure to always spare time for them. Squash, football, cricket, tennis, and racing are the hobbies he loves to spend his time in.

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