Silicon Timepiece Spring Strength via Thermal Oxidation
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Solution Overview
Problem
Silicon-based timepiece springs face mechanical strength limitations due to defects from deep reactive ion etching, leading to breakage risks under operational stresses, especially in high-stress applications like mainsprings and barrel springs, where materials with higher elastic limits are typically required.
Innovation Solution
A method involving thermal oxidation, deoxidation, annealing in a reducing atmosphere, and subsequent silicon oxide layer formation to enhance the mechanical strength and fatigue resistance of silicon-based timepiece springs, which includes etching, thermal oxidation, removing the oxide layer, annealing to round off defects, and re-forming a silicon oxide layer to improve surface integrity and compressive stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If deep reactive ion etching is used to machine silicon components, then manufacturing precision is improved, but mechanical strength deteriorates due to sharp edges and crystalline defects
Solution Approach 1:
The patent applies preliminary thermal oxidation before etching to create a protective oxide layer on the silicon surface. This layer is then removed after etching, but the oxidation process has already rounded the sharp edges and reduced stress concentration points that would otherwise lead to breakage during handling and operation.
Solution Approach 2:
The patent changes the physical and chemical parameters of the silicon surface through thermal oxidation, transforming the sharp, defect-prone etched surface into a rounded, oxide-coated surface with reduced stress concentration. The oxidation temperature and duration are controlled to achieve optimal edge rounding without excessive material removal.
2Strength
If silicon oxide coating is applied to strengthen silicon components, then mechanical strength is improved, but device complexity increases due to additional coating steps
Solution Approach 1:
The patent merges the edge-rounding function and the strengthening function into a single thermal oxidation step. The oxide layer serves dual purposes: it rounds the sharp edges created by etching and simultaneously provides the compressive stress needed to prevent breakage, eliminating the need for separate coating processes.
Solution Approach 2:
The silicon substrate itself serves to create the protective layer through thermal oxidation. The silicon reacts with oxygen in the atmosphere to form the protective oxide coating, using the substrate material's own properties to generate the strengthening layer rather than requiring external coating materials or complex deposition equipment.
3Weight of moving object
If silicon is used for high-stress springs like mainsprings, then weight is reduced, but reliability deteriorates due to insufficient elastic limit under high operational stresses
Solution Approach 1:
The patent fundamentally changes the stress state parameters of the silicon spring by introducing compressive residual stress through thermal oxidation. This transforms the stress-strain behavior of the silicon, allowing it to withstand the high operational stresses of mainsprings and other high-load components without exceeding its elastic limit, thereby enabling reliable use in applications previously unsuitable for silicon.
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
The method significantly increases the apparent breaking stress of silicon-based timepiece springs to levels comparable to high-performance alloys, enabling them to withstand high-intensity forces and reduce fatigue, resulting in springs with enhanced operational durability and reduced defect-related failures.
Implementation Method 1
b) thermally oxidising the piece
Implementation Method 2
d) annealing the piece in a reducing atmosphere
Data Source
AI summary
A method for producing a timepiece spring includes the following steps: producing a piece based on silicon, having the desired shape of the timepiece spring; thermally oxidising the piece; deoxidising the piece; annealing the piece in a reducing atmosphere; forming a silicon oxide layer on the piece.