A 600 °C TTL-based 11-stage Ring Oscillator in Bipolar Silicon Carbide Technology

Abstract

Ring oscillators (ROs) are used to study the high-temperature characteristics of an in-house silicon carbide (SiC) technology. Design and successful operation of the in-house-fabricated 4H-SiC n-p-n bipolar transistors and TTL inverter-based 11-stage RO are reported from 25 °C to 600 °C. Non-monotonous temperature dependence was observed for the oscillator frequency; in the range of 25 °C to 300 °C, it increased with the temperature (1.33 MHz at 300 °C and $V_{CC} =15$ V), while it decreased in the range of 300 °C–600 °C. The oscillator output frequency and delay were also characterized over a wide range of supply voltage (10 to 20 V). The noise margins of the TTL inverter were also measured; noise margin low ( $\text {NM}_{L}$ ) decreases with the temperature, whereas noise margin high ( $\text {NM}_{H}$ ) increases with the temperature. The measured power-delay product ( ${P}_{D} \cdot {T}_{P}$ ) of the TTL inverter and 11-stage RO was ≈ 4.5 and ≈285 nJ, respectively, at ${V}_{\text {CC}} =15$ V. Reliability testing indicated that the RO frequency of oscillation decreased 16% after HT characterization.