A 0.55-THz on-chip near-field edge-sensing probe in 130-nm SiGe technology

Abstract This work presents a terahertz (THz) single-pixel near-field sensor fabricated in 130-nm SiGe BiCMOS technology, which operates from a diced chip edge. The proposed sensor integrates a triple-push Colpitts oscillator serving as the THz source, a passive sensing structure based on coupled transmission lines, and an on-chip power detector with an operating frequency of approximately 547 GHz. A monotonic mapping between permittivity variation and DC output voltage of the detector is achieved, enabling amplifier-free direct sensing. In contrast to conventional top surface-sensing near-field sensors, the proposed edge-sensing architecture offers greater scanning flexibility. The sensor demonstrates super-resolution imaging performance, achieving horizontal and vertical spatial resolutions of 12 and 7 backslash unicodex 03 BC $\unicode{x03BC}$ \unicode x 03 B C m, respectively, along with a signal-to-noise ratio of 28.5 dB with a 2 kHz ADC sampling rate. When operated as a permittivity sensor, measurements performed on a float-zone silicon wafer exhibit a deviation of 6.8% compared to results obtained using a Toptica continuous-wave frequency-domain THz spectroscopy system, indicating good agreement. Moreover, with appropriately controlled laser dicing, the sensor is expected to function as a near-field sensing probe with a reduced sensing part area at the chip edge. This approach could enable surface-following capability, making the proposed sensor potentially suitable for the characterization of nonplanar microstructures.