Suppressing Period Doubling in Pre-patterned Thin Film Wrinkles

Solution Overview

Problem

The existing methods for fabricating stretch-tunable micro and nano structures via wrinkling of thin films face limitations in the feasible range of strain due to the phenomenon of period doubling at high strains, which is undesirable for applications requiring single-period structures.

Innovation Solution

The method involves pre-patterning bilayers with a period matching the natural period of the equivalent flat bilayer, suppressing period doubling by controlling the amplitude of the pre-patterns, thereby increasing the operating range of stretch-tunable wrinkle-based devices.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the compressive strain is increased beyond the nominal onset strain to achieve higher stretch-tenability, then the amplitude of wrinkles increases, but period doubling occurs and the single-period structure transitions into a two-period structure

Engineering Contradiction:

Improvestretch-tenabilityVSAvoidsingle-period structure

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The invention applies preliminary action by pre-patterning the substrate with a sinusoidal pattern before forming the thin film. This pre-pattern is created at a strain level that corresponds to the desired high-strain wrinkle amplitude, ensuring that the structure maintains its single-period configuration even when compressed to high strains, thereby preventing period doubling

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention changes the geometric parameters of the system by introducing a pre-pattern with specific amplitude and period ratios. By controlling the pre-pattern amplitude to be at least 15% of the pre-pattern period, the system's strain response is modified to suppress period doubling and maintain structural stability at high compressive strains

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If pre-stretch is increased to suppress period doubling using material stiffness dependence, then period doubling is suppressed, but material selection is limited due to reliance on 2nd order nonlinear effects

Engineering Contradiction:

Improvesingle-period structureVSAvoidmaterial selection

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The invention changes the geometric parameters of the system by introducing a pre-pattern with specific amplitude and period ratios. By controlling the pre-pattern amplitude to be at least 15% of the pre-pattern period, the system's strain response is modified to suppress period doubling and maintain structural stability at high compressive strains

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention applies preliminary action by pre-patterning the substrate with a sinusoidal pattern before forming the thin film. This pre-pattern is created at a strain level that corresponds to the desired high-strain wrinkle amplitude, ensuring that the structure maintains its single-period configuration even when compressed to high strains, thereby preventing period doubling

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach effectively suppresses period doubling, allowing the wrinkle-based devices to operate beyond the nominal onset strain, increasing the feasible range of strain by at least a factor of 1.5, and maintaining a single-period structure even at high compressive strains.

Implementation Method 1

Sinusoidal periodic wrinkled patterns are formed via compression of supported thin films as a result of buckling-based instabilities and the mechanism is similar to Euler buckling of beams under compressive loads

Methodology Applied

Scientific EffectBuckling-based instability:

Implementation Method 2

mismatch in the elastic moduli of the film and the base with the film being stiffer than the base

Methodology Applied

Scientific EffectElastic modulus mismatch:

Data Source

PatentUS10144172B2Method to suppress period doubling during manufacture of micro and nano scale wrinkled structures

Publication Date: 2018.12.04 SAHA SOURABH KUMAR

AI summary

The range of stretch-tunability of sinusoidal wrinkled surfaces that are obtained by compression of supported thin films is limited by the emergence of a period-doubled mode at high compressive strains. This disclosure presents a method to suppress the emergence of the period-doubled mode at high strains. This is achieved by compressing pre-patterned supported thin films, wherein the pre-patterns are substantially similar to the natural pattern of the supported thin film system. As compared to flat thin film systems, pre-patterned thin film systems exhibit period doubling behavior at a higher compressive strain. The onset strain for emergence of period-doubling is tuned by altering the amplitude of the pre-patterns.