Development of LTCC-packaged optocouplers as optical galvanic isolation for high-temperature applications

This paper reports high-temperature optocouplers for signal galvanic isolation. Low temperature co-fired ceramic (LTCC) technology was used in the design and fabrication of the high-temperature optocoupler package. The optimal coupling behaviors, driving capabilities and response speed of the optocouplers were concentrated and investigated in this paper. Emitters and detectors with different emission and spectral wavelengths were studied to achieve optimal coupling behaviors. Relatively high coupling efficiency is achieved with emitters and detectors of emission and spectral wavelength in the red spectrum (i.e., 620-750 nm), leading to higher current transfer ratios (CTR). To further enhance the electrical performance, optocouplers with multiple detectors in parallel were designed and fabricated. CTR, leakage current and response speed (i.e., propagation delay, rise time and fall time) of the optocouplers were characterized over a range of temperatures from 25 to 250 °C. The CTR degrades at high temperatures, while the leakage current and response speed show little degradation with varying temperatures. Furthermore, the behaviors of the optocouplers with varying temperatures are modeled and analyzed.