Implementation of Low Temperature Co-Fired Ceramic Packages for All Solid-State Hydrogen Sensor Modules

Abstract

We have implemented LTCC (Low Temperature Co-Fired Ceramics) based packages for all solid-state electrochemical hydrogen sensor modules. The hydrogen sensor utilizing a solid electrolyte is designed to have a hetero-junction structure of a proton conductor and an oxygen ion conductor. LTCC is a composite material of ceramic powders and glass frits, and can be sintered at a low temperature of 900 °C or less, and has superior electrical, mechanical, and thermal properties compared to PCB. In this study, we developed a package technology for hydrogen sensor modules using this LTCC material. A double layer structure is used to form the package, and in the bottom plate, a mount for the hydrogen sensor, line guides for air flow, and guides to support the wires are fabricated. Laser pulses are employed to form 3D structures of LTCC including the mounting cavities and vias to connect the metal electrodes of the sensor. The hydrogen sensor is mounted in the center of the bottom plate and connected to the Ag/Pt electrode formed at the backside of the plate through 4 wires and via holes. The measurement results to check the hydrogen response of the sensors using LTCC packages show that the solid-state electrochemical voltage change from 248.2 ∼ 296.4 mV to 472.8 ∼ 554.5.2 mV for hydrogen concentration from 0.5 to 4.0% in the air. The electrochemical voltage of this sensor is linearly proportional to the logarithm of the hydrogen partial pressure. The reproducibility tests show that the change of the sensitivity of the sensor was within 4.3% deviation for 3 times repeat test. This reaction sensitivity remains the same with a deviation of less than 1.2% in the test even after 52 days. In the thermal shock test for environmental evaluation, all hydrogen sensor packages fabricated in this study show normal operation.