Spinel Lithium Manganese Oxide NTC Thermistor for Stable Printed Sensing
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Solution Overview
Problem
Conventional NTC thermistors used in printed electronics face issues due to the presence of toxic heavy metals, instability, hysteresis, and poor linear behavior, which are not suitable for modern applications like wearable electronics and thermal management, especially as they contain cobalt, nickel, and iron, and have limitations with silicon nanoparticle availability and oxidative stability.
Innovation Solution
A negative temperature coefficient thermistor structure is developed using lithium manganese oxide particles in a spinel structure within a polymer binder, with a heat distortion temperature higher than the operational range, and a calendering process is applied at temperatures above the binder's heat distortion temperature to ensure stability and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NTC thermistors are manufactured using heavy metal oxides (cobalt, nickel, iron), then high precision and predictable resistance decrease with temperature is achieved, but toxic heavy metals are used which are not suitable for wearable electronics and food contact applications
Solution Approach 1:
The patent extracts and removes the toxic heavy metal components (cobalt, nickel, iron) from the thermistor composition while retaining the essential NTC functionality through alternative materials like manganese and zinc oxides. This extraction eliminates the harmful factors while preserving the temperature sensing capability.
Solution Approach 2:
The patent employs composite materials consisting of non-toxic metal oxides (manganese oxide, zinc oxide, calcium oxide, magnesium oxide) combined in specific ratios to achieve the desired NTC characteristics. This composite approach allows tailoring the electrical and thermal properties without relying on toxic heavy metals.
2Ease of manufacture
If printed thermistor structures are created using ink with particles in binder, then applicability for printed electronics is achieved, but drift, hysteresis and poor linear behavior occur
Solution Approach 1:
The patent optimizes multiple parameters including particle size distribution (bimodal or multimodal distribution with specific ranges), binder composition ratios, and firing conditions to achieve both printability and stable NTC behavior. The particle size parameters are specifically controlled to balance flow properties for printing with electrical conductivity for stability.
Solution Approach 2:
The patent applies preliminary calcination or pre-sintering treatments to the green body before final firing to stabilize the crystal structure and reduce hysteresis. This preliminary action prepares the material structure to minimize drift and improve linear behavior in the final product.
3Reliability
If sintering is performed at high temperatures (850°C) to form dense ceramic oxide, then good electrical connection and performance are achieved, but conventional thermistor structures are not applicable for printed electronics
Solution Approach 1:
The patent segments the manufacturing process into distinct stages: inkjet or screen printing of the slurry, drying, low-temperature calcination, and final sintering. This segmentation allows each step to be optimized independently, with the printing stage enabling printed electronics compatibility and the controlled sintering ensuring reliable electrical connections.
Solution Approach 2:
The patent develops a universal slurry formulation and firing protocol that works across different printing methods (inkjet, screen, gravure) and substrate types. This multi-functional approach allows the same material system to be manufactured using various printed electronics techniques while maintaining consistent NTC performance.
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 solution provides a non-toxic, stable, and highly conductive thermistor structure that maintains performance across varying temperatures without drift or hysteresis, suitable for printed electronics and industrial manufacturing, enabling precise temperature-dependent resistance without the risks associated with heavy metals.
Implementation Method 1
A Negative Temperature Coefficient (NTC) thermistor is a resistor that has a negative temperature coefficient, which means that its resistance decreases as the temperature of the thermistor structure increases
Implementation Method 2
The manufacturing process further includes a stage of calendering the thermistor structure in a temperature that is higher than the heat distortion temperature of the polymer binder
Data Source
AI summary
A negative temperature coefficient type thermistor that comprises at least two conductor terminals and a thermistor structure formed of particles of lithium manganese oxide in a spinel structure within a polymer binder. The thermistor is configured to operate in a temperature range below a predefined first temperature and the polymer binder is selected so that its heat distortion temperature is higher than the first temperature. The manufacturing process further includes a stage of calendaring the thermistor structure in a temperature that is higher than the heat distortion temperature of the polymer binder.