Lithium Tantalate Substrate Resistivity Control via Reused Carbonate
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Solution Overview
Problem
The reuse of lithium carbonate powder in reducing lithium tantalate substrates often results in insufficient reduction, leading to increased volume resistivity, which can fluctuate beyond the desired range of 1×10^10 Ω·cm to 1×10^12 Ω·cm.
Innovation Solution
A method involving heat-treating lithium tantalate single crystal substrates with a used lithium carbonate powder having a BET specific surface area of 0.13 m2/g or more, in a mixed gas atmosphere of inert and reducing gases, followed by a single gas atmosphere of inert gas, under controlled temperature and humidity conditions to maintain optimal volume resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lithium carbonate powder is reused in reduction of lithium tantalate substrate, then cost is reduced and productivity is improved, but volume resistivity increases and becomes unstable
Solution Approach 1:
The patent applies parameter changes by controlling the BET specific surface area of the lithium carbonate powder (maintaining it at 0.05 m²/g or more) and specifying the heat treatment temperature range (350°C to Curie temperature). These parameter controls ensure that even when lithium carbonate powder is reused, it maintains sufficient reducing capability to achieve the target volume resistivity of 1×10¹⁰ to 1×10¹² Ω·cm, thus resolving the contradiction between reusability and resistivity control.
2Manufacturing precision
If heat treatment temperature is increased to improve reduction effect, then volume resistivity decreases, but risk of exceeding Curie temperature and damaging the substrate increases
Solution Approach 1:
The patent specifies a precise temperature parameter range for heat treatment: 350°C or higher but not higher than the Curie temperature of lithium tantalate. This parameter control enables sufficient reduction to achieve the desired volume resistivity (1×10¹⁰ to 1×10¹² Ω·cm) while avoiding excessive temperature that would cause domain structure changes or substrate damage, thus resolving the contradiction between reduction effectiveness and substrate safety.
3Manufacturing precision
If lithium carbonate powder with high BET specific surface area is used initially, then reduction effect is good, but the powder loses its reducing capability after reuse
Solution Approach 1:
The patent identifies and controls the BET specific surface area parameter, specifying it should be 0.05 m²/g or more. This parameter control ensures that the lithium carbonate powder maintains adequate reducing capability throughout its service life, including after reuse. By monitoring and maintaining this surface area parameter, the patent extends the usable life of the lithium carbonate powder while ensuring consistent reduction quality, thus resolving the contradiction between initial effectiveness and durability.
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 method effectively suppresses the increase in volume resistivity, ensuring the lithium tantalate single crystal substrates maintain a stable resistivity within the desired range, even when the lithium carbonate powder is reused.
Implementation Method 1
a method for producing a lithium tantalite single crystal substrate having a highly homogeneous volume resistivity by buried reduction of a lithium tantalate single crystal substrate in a lithium carbonate powder
Implementation Method 2
the heat treatment is carried out in a mixed gas atmosphere of an inert gas and a reducing gas at the start of the heat treatment
Data Source
AI summary
Provided is a method for producing a lithium tantalate single crystal substrate capable of suppressing increase in volume resistivity of the lithium tantalate single crystal substrate owing to reduction failure even when a lithium carbonate power is repeatedly used in heat treatment for the lithium tantalate single crystal substrate. The invention is a method for producing a lithium tantalate single crystal substrate having a volume resistivity of 1×1010 Ω·cm or more and less than 1×1012 Ω·cm, including a step of heat-treating a lithium tantalate single crystal substrate having a volume resistivity of 1×1012 Ω·cm or more and having a single-domain structure, under normal pressure and at a temperature of 350° C. or higher but not higher than the Curie temperature thereof while burying it in a lithium carbonate powder having a BET specific surface area of 0.13 m2/g or more, wherein the lithium carbonate powder is a used lithium carbonate powder that has been used in burying a lithium tantalate single crystal substrate in heat treatment for the lithium tantalate single crystal structure under normal pressure and at a temperature of 350° C. or higher but not higher than the Curie temperature thereof, and in the heat treatment step, the heat treatment is carried out in a mixed gas atmosphere of an inert gas and a reducing gas at the start of the heat treatment, and after the heat treatment in the mixed gas atmosphere, the heat treatment is carried out in a single gas atmosphere of an inert gas.