Silicon Microneedles With Controllable Bevelled Tips
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Solution Overview
Problem
Existing methods for fabricating silicon microneedles using plasma etch techniques are prone to mechanical failure, lack flexibility in length and pitch variation, and struggle to produce bevelled tips reliably, with fixed bevel angles due to crystallographic constraints and long processing times.
Innovation Solution
A method involving SF6 based plasma etch and DRIE processes to create silicon microneedles with user-selectable, controllable bevel angles, using multiple mask arrangements and etch techniques to achieve desired tip shapes and penetration properties, allowing for flexible design and reduced processing times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If wet etch technique using potassium hydroxide is used to create bevelled tip microneedles, then bevelled tips can be formed, but the bevel angle is fixed at 57.4° due to crystallographic nature and processing time is long
Solution Approach 1:
The patent changes the etching parameters by switching from wet etch to plasma etch process, and further to DRIE process, enabling continuous adjustment of bevel angle from 0° to 90° rather than being fixed at 57.4°. This parameter change allows independent control of bevel angle from crystallographic orientation while maintaining the bevelled tip shape.
Solution Approach 2:
The patent replaces the chemical wet etching mechanism with a plasma-based DRIE process. This substitution enables precise control over etching depth and angle through process parameters rather than being constrained by crystallographic planes, achieving variable bevel angles while reducing processing time.
2Productivity
If plasma etch techniques are used to fabricate silicon microneedles, then processing time is reduced, but the techniques are prone to mechanical failure and lack flexibility in length and pitch variation
Solution Approach 1:
The patent optimizes plasma etch parameters including gas composition (SF6 based), pressure, power, and temperature to achieve reliable microneedle fabrication. By carefully controlling these parameters, the process achieves both high productivity and mechanical reliability, preventing the mechanical failure issues that plague conventional plasma etching methods.
Solution Approach 2:
The patent introduces dynamic control capabilities allowing variation in microneedle length and pitch through programmable mask patterns and adjustable etching parameters. This dynamic approach enables flexible design while maintaining the speed advantages of plasma etching, overcoming the rigidity limitations of traditional methods.
3Shape
If conventional plasma etch techniques are used with mask erosion defining wall angle, then sloped profiles can be achieved, but etch rates are very low and mask thickness severely restricts etch depth
Solution Approach 1:
The patent replaces the mask-erosion-based angle definition with a direct plasma etching mechanism where ion bombardment and chemical reactions create the sloped profile. This substitution eliminates the dependency on mask thickness and enables both high etch rates and precise angle control through plasma parameter adjustment rather than mechanical mask constraints.
Solution Approach 2:
The patent changes the fundamental etching mechanism from mask-limited to plasma-parameter-controlled by adjusting gas flow rates, RF power, and pressure. This parameter optimization achieves high etch rates while maintaining precise sloped profile formation, overcoming the severe restrictions imposed by mask thickness in conventional approaches.
4Ease of operation
If microneedles are made with length of a few hundred microns for painless insertion, then skin penetration is achieved with low nerve receptor density, but penetration reliability is insufficient without proper bevelled tips
Solution Approach 1:
The patent employs asymmetrical bevelled tip designs where one side of the microneedle tip has a different angle than the other. This asymmetry creates optimized stress distribution during insertion, enabling reliable penetration through skin at shallow angles while maintaining the short length required for painless operation in superficial layers with low nerve receptor density.
Solution Approach 2:
The patent optimizes the bevel angle parameter to specific ranges that maximize penetration reliability for short microneedles. By controlling the bevel angle independently of crystallographic orientation, the process achieves the precise geometric parameters needed for reliable skin penetration while maintaining the short overall length that ensures painless insertion.
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
Enables the production of microneedles with improved design flexibility, enhanced penetration properties, and reduced processing times, overcoming limitations of traditional wet etch techniques by achieving variable bevel angles and tip shapes, resulting in more effective skin penetration and drug delivery.
Implementation Method 1
performing a SF6 based plasma etch of the first face through the gaps in the first mask arrangement to provide one or more etch features having a sloping face
Implementation Method 2
performing a DRIE (deep reactive ion etch) anisotropic plasma etch of the etched front face of the substrate to form a plurality of microneedles which have a bevelled tip
Data Source
AI summary
A method is for manufacturing a plurality of silicon microneedles which have a bevelled tip. The method includes providing a silicon substrate having a front face and a rear face, forming a first mask arrangement on the front face of the substrate, the first mask arrangement defining one or more gaps, and performing a SF6 based plasma etch of the front face through the gaps in the first mask arrangement to provide one or more etch features having a sloping face. The SF6 based plasma etch undercuts the first mask arrangement with an undercut that is at least 10% of the depth of a corresponding etch feature. The method further includes forming a second mask arrangement on the etch features to define locations of the microneedles, in which the second mask arrangement is located entirely on sloping faces of the etch features, and performing a DRIE (deep reactive ion etch) anisotropic plasma etch of the etched front face of the substrate to form a plurality of microneedles which have a bevelled tip, where the sloping faces of the etch features at least in part give rise to the bevelled tips of the microneedles.