Pulsed DC Sputtering of Piezoelectric Films
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Solution Overview
Problem
The fabrication of piezoelectric layers, particularly relaxor-PT, using physical vapor deposition is challenging due to target overheating and damage, leading to defects and increased downtime in semiconductor fabrication plants, and existing methods like sol-gel techniques are time-consuming and not conducive for large-area deposition.
Innovation Solution
A method involving physical vapor deposition where the target is kept at a lower temperature by alternating power application and cooling phases, followed by thermal annealing to achieve a desired crystalline structure, reducing target damage and enabling uniform stoichiometry and phase conversion of PMNPT for superior piezoelectric properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous power is applied to the target during physical vapor deposition, then deposition rate is improved, but target overheating and damage occur
Solution Approach 1:
The patent implements periodic pulsed DC power application to the target, alternating between on-periods (applying power for deposition) and off-periods (allowing target cooling). This periodic action maintains adequate deposition rates while preventing target overheating and damage by providing regular cooling intervals.
Solution Approach 2:
The patent dynamically adjusts the pulsed DC power parameters (on-period duration, off-period duration, power level) based on target temperature conditions and deposition requirements. This dynamic control optimizes both deposition rate and target temperature management, resolving the contradiction between productivity and reliability.
2Ease of manufacture
If sol-gel techniques are used to deposit piezoelectric layers, then material deposition is achieved, but processing time increases
Solution Approach 1:
The patent replaces the multi-step chemical sol-gel process with direct physical vapor deposition using pulsed DC sputtering. This substitution eliminates lengthy drying, firing, and multiple deposition cycles required by sol-gel techniques, achieving comparable material deposition in significantly reduced time while maintaining film quality.
3Speed
If high power is applied to the target, then deposition speed increases, but target temperature rises causing defects
Solution Approach 1:
The patent uses periodic pulsed DC power with controlled on-periods and off-periods to deliver high power during deposition while allowing target cooling during off-periods. This prevents excessive temperature accumulation that would cause defects, while maintaining high average deposition speed through efficient on-period power delivery.
Solution Approach 2:
The patent maintains continuous deposition action through optimized pulsed DC cycling, where the on-periods are sufficiently long to achieve high deposition rates and the off-periods are optimized for cooling without interrupting the overall deposition process. This ensures continuous useful action with minimal interruption to deposition speed.
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 allows for the fabrication of piezoelectric layers with improved properties, reducing defects and downtime, and achieving uniform crystalline phases across large areas, while limiting parasitic phases like PbOx and pyrochlore, thus enhancing the commercial viability of piezoelectric device production.
Implementation Method 1
a power supply configure to apply power to the target to generate a plasma in the chamber to sputter material from the target onto the substrate to form a piezoelectric layer on the substrate
Implementation Method 2
a power supply configure to apply power to the target to generate a plasma in the chamber
Implementation Method 3
thermally annealing the substrate at a temperature above 500° C. to convert the piezoelectric material to a second crystallographic phase
Implementation Method 4
to convert the piezoelectric material to a second crystallographic phase
Data Source
AI summary
A physical vapor deposition system includes a deposition chamber, a support to hold a substrate in the deposition chamber, a target in the chamber, a power supply configured to apply power to the target to generate a plasma in the chamber to sputter material from the target onto the substrate to form a piezoelectric layer on the substrate, and a controller configured to cause the power supply to alternate between deposition phases in which the power supply applies power to the target and cooling phases in which power supply does not apply power to the target. Each deposition phase lasts at least 30 seconds and each cooling phase lasts at least 30 seconds.