arXiv subjects

Jakob Holstein

Publications and source records attributed to Jakob Holstein.

5 recordsLinked to original sources

arXiv2025

Improving terahertz-detection sensitivity of 8x8 FET arrays through liquid-nitrogen cooling in a compact low-noise cryostat

We show that the sensitivity of antenna-coupled field-effect transistors (FETs) to terahertz (THz) radiation improves continuously with decreasing temperature. The noise-equivalent power (NEP) of 540 GHz patch-antenna-coupled FETs decreases as temperature reduces to 20 K. We project NEP values approaching 1 to 2 pW/sqrt(Hz) under efficient power coupling conditions (e.g., using a superstrate Si-lens), which is comparable to superconducting niobium transition-edge sensors (TESs) at 4 K. Building on these findings, a compact, low-noise, liquid-nitrogen-cooled (77 K) FET-based direct (incoherent) THz-power sensing system} for spectroscopy applications was realized. Here, an 8x8 pixel-binned detector array fabricated in a commercial 65-nm Si-CMOS process, was optimized for operation in the 2.85 to 3.4 THz band. Characterization was performed in the focal plane of a 2.85-THz quantum-cascade laser delivering approx. 2~mW of THz power. A linear dynamic range exceeding 67 dB was achieved without saturation (for 1~Hz-detection bandwidth). The system provides a -3 dB readout bandwidth of 5 MHz, exceeding that of conventional thermal detectors (typically 1 kHz). Combined with its broad temperature operability 20 K to 300 K and compact design, the system is particularly well suited for space- and payload-constrained platforms such as balloon- and satellite-based missions, where deep cryogenic cooling is impractical.

physics.app-ph↗

arXiv2024

8x8 Patch-Antenna-Coupled TeraFET Detector Array for Terahertz Quantum-Cascade-Laser Applications

Monolithically integrated, antenna-coupled field-effect transistors (TeraFETs) are rapid and sensitive detectors for the terahertz range (0.3-10~THz) that can operate at room temperature. We conducted experimental characterizations of a single patch-antenna coupled TeraFET optimized for 3.4~THz operation and its integration into an 8x8 multi-element detector configuration. In this configuration, the entire TeraFET array operates as a unified detector element, combining the output signals of all detector elements. Both detectors were realized using a mature commercial Si-CMOS 65-nm process node. Our experimental characterization employed single-mode Quantum-Cascade Lasers (QCLs) emitting at 2.85~THz and 3.4~THz. The 8x8 multi-element detector yields two major improvements for sensitive power detection experiments. First, the larger detector area simplifies alignment and enhances signal stability. Second, the reduced detector impedance enabled the implementation of a TeraFET+QCL system capable of providing a -3~dB modulation bandwidth up to 21~MHz, which is currently limited primarily by the chosen readout circuitry. Finally, we validate the system's performance by providing high resolution gas spectroscopy data for methanol vapor around 3.4~THz, where a detection limit of 1.6e-5 absorbance, or 2.6e11~molecules/cm^3 was estimated under optimal coupling conditions.

physics.ins-det↗

arXiv2024

Si Superstrate Lenses on Patch-Antenna-Coupled TeraFETs: NEP Optimization and Frequency Fine-Tuning

This paper presents a study on performance optimization and resonant frequency modification of terahertz detectors by the use of hyper-hemispherical silicon superstrate lenses. The detectors are patch-TeraFETs, i.e., field-effect transistors with monolithically integrated patch antennas fabricated with a commercial 65-nm CMOS foundry process and designed for an operation frequency of 580 GHz. We demonstrate a strong improvement of the optical noise-equivalent power optical NEP, referenced against the total radiation power) reaching a value of 16 pW/Hz^(1/2). We show, furthermore, that the resonance frequency can be efficiently fine-tuned by the choice of the material and the thickness of a dielectric layer placed between the transistor and the superstrate lens. The resonance frequency can be shifted by more than 15 % of the center frequency (up to 100 GHz for the 580 GHz devices). The design of the on-chip optics can be employed for post-fabrication tailoring of the detector's resonance frequency to target specific spectral positions.

physics.optics↗

arXiv2024

Modeling of antenna-coupled Si MOSFETs in the Terahertz Frequency Range

We report on the modeling and experimental characterization of Si CMOS detectors of terahertz radiation based on antenna-coupled field-effect transistors (TeraFETs). The detectors are manufactured using TSMC's 65-nm technology. We apply two models -- the TSMC RF foundry model and our own ADS-HDM -- to simulate the Si CMOS TeraFET performance and compare their predictions with respective experimental data. Both models are implemented in the commercial circuit simulation software Keysight Advanced Design System (ADS). We find that the compact model TSMC RF is capable to predict the detector responsivity and its dependence on frequency and gate voltage with good accuracy up to the highest frequency of 1.2 THz covered in this study. This frequency is well beyond the tool's intended operation range for 5G communications and 110-GHz millimeter wave applications. We demonstrate that our self-developed physics-based ADS-HDM tool, which relies on an extended one-dimensional hydrodynamic transport model and can be adapted readily to other material technologies, has high predictive qualities comparable to those of the foundry model. We use the ADS-HDM to discuss the contribution of diffusive and plasmonic effects to the THz response of Si CMOS TeraFETs, finding that these effects, while becoming more significant with rising frequency, are never dominant. Finally, we estimate that the electrical NEP (perfect power coupling conditions) is on the order of 5 pW/$\sqrt{\rm{Hz}}$ at room-temperature.

physics.app-ph↗

arXiv2024

Terahertz detection with graphene FETs: photothermoelectric and resistive self-mixing contributions to the detector response

Field-effect transistors coupled to integrated antennas (TeraFETs) are photodetectors being actively developed for the THz frequency range ($\sim$ 100 GHz - 10 THz). Among them, Graphene TeraFETs (G-TeraFETs) have demonstrated distinctive photoresponse features compared to those made from elementary semiconductors. For instance, previous studies have shown that G-TeraFETs exhibit a THz response that comprises two components: the resistive self-mixing (RSM) and photothermoelectric effect (PTE). The RSM and PTE arise from carrier density oscillations and carrier heating, respectively. In this work, we confirm that the photoresponse can be considered a combination of RSM and PTE, with PTE being the dominant rectification mechanism at higher frequencies. For our CVD G-TeraFETs with asymmetric antenna coupling, the PTE response dominates over the RSM at frequencies above 100 GHz. We find that relative contribution of RSM and PTE to the photoresponse is strongly frequency dependent. Electromagnetic wave simulations show that this behavior is due to the relative change in the total dissipated power between the gated and ungated channel regions of the G-TeraFET as the frequency increases. The simulations also indicate that the channel length over which the PTE contributes to the photoresponse below the gate electrode is approximately the same as the electronic cooling length. Finally, we identify a PTE contribution that can be attributed to the contact doping effect in graphene close to the metal contacts. Our detectors achieve a minimum optical noise-equivalent power of 101 (114) pW/$\sqrt{Hz}$ for asymmetric (symmetric) THz antenna coupling conditions at 400 GHz. This work demonstrates how the PTE response can be used to optimize the THz responsivity of G-TeraFETs.

cond-mat.mes-hall↗