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1. Illuminating Trap Density Trends in Amorphous Oxide Semiconductors with Ultrabroadband Photoconduction

   https://doi.org/10.1002/adfm.202300742  

   Mattson, George_W; Vogt, Kyle_T; Wager, John_F; Graham, Matt_W (March 2023, Advanced Functional Materials)

   Abstract Under varying growth and device processing conditions, ultrabroadband photoconduction (UBPC) reveals strongly evolving trends in the defect density of states (DoS) for amorphous oxide semiconductor thin‐film transistors (TFTs). Spanning the wide bandgap of amorphous InGaZnO_x(a‐IGZO), UBPC identifies seven oxygen deep donor vacancy peaks that are independently confirmed by energetically matching to photoluminescence emission peaks. The subgap DoS from 15 different types of a‐IGZO TFTs all yield similar DoS, except only back‐channel etch TFTs can have a deep acceptor peak seen at 2.2 eV below the conduction band mobility edge. This deep acceptor is likely a zinc vacancy, evidenced by trap density which becomes 5‐6× larger when TFT wet‐etch methods are employed. Certain DoS peaks are strongly enhanced for TFTs with active channel processing damage caused from plasma exposure. While Ar implantation and He plasma processing damage are similar, Ar plasma yields more disorder showing a ≈2 × larger valence‐band Urbach energy, and two orders of magnitude increase in the deep oxygen vacancy trap density. Changing the growth conditions of a‐IGZO also impacts the DoS, with zinc‐rich TFTs showing much poorer electrical performance compared to 1:1:1 molar ratio a‐IGZO TFTs owing to the former having a ∼10 × larger oxygen vacancy trap density. Finally, hydrogen is found to behave as a donor in amorphous indium tin gallium zinc oxide TFTs. 

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2. An Analytical Model for Dual Gate Piezoelectrically Sensitive ZnO Thin Film Transistors

   https://doi.org/10.1002/admt.202100224  

   Oh, Hongseok; Dayeh, Shadi_A (June 2021, Advanced Materials Technologies)

   Abstract Highly sensitive force sensors of piezoelectric zinc oxide (ZnO) dual‐gate thin film transistors (TFTs) are reported together with an analytical model that elucidates the physical origins of their response. The dual‐gate TFTs are fabricated on a polyimide substrate and exhibited a field effect mobility of ≈5 cm²V⁻¹s⁻¹,I_max/I_minratio of 10⁷, and a subthreshold slope of 700 mV dec⁻¹, and demonstrated static and transient current changes under external forces with varying amplitude and polarity in different gate bias regimes. To understand the current modulation of the dual‐gate TFT with independently biased top and bottom gates, an analytical model is developed. The model includes accumulation channels at both surfaces and a bulk channel within the film and accounts for the force‐induced piezoelectric charge density. The microscopic piezoelectric response that modulates the energy‐band edges and correspondent current–voltage characteristics are accurately portrayed by this model. Finally, the field‐tunable force response in single TFT is demonstrated as a function of independent bias for the top and bottom gates with a force response range from −0.29 to 22.7 nA mN⁻¹. This work utilizes intuitive analytical models to shed light on the correlation between the material properties with the force response in piezoelectric TFTs. 

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3. Atomic layer self-transducing MoS2 vibrating channel transistors with 0.5 pm/Hz1/2 displacement sensitivity at room temperature

   https://doi.org/10.1063/5.0170127  

   Yousuf, S_M_Enamul Hoque; Feng, Philip X-L (January 2024, Applied Physics Letters)

   We report on the experimental demonstration of high-performance suspended channel transistors with single- and bilayer (1L and 2L) molybdenum disulfide (MoS2), and on operating them as vibrating channel transistors (VCTs) and exploiting their built-in dynamic electromechanical coupling to read out picoampere (pA) transconduction current directly at the vibrating tones, without frequency conversion or down-mixing, for picometer (pm)-scale motion detection at room temperature. The 1L- and 2L-MoS2 VCTs exhibit excellent n-type transistor behavior with high mobility [150 cm2/(V·s)] and small subthreshold swing (98 mV/dec). Their resonance motions are probed by directly measuring the small-signal drain-source currents (iD). Electromechanical characteristics of the devices are extracted from the measured iD, yielding resonances at f0 = 31.83 MHz with quality factor Q = 117 and f0 = 21.43 MHz with Q = 110 for 1L- and 2L-MoS2 VCTs, respectively. The 2L-MoS2 VCT demonstrates excellent current and displacement sensitivity (Si1/2 = 2 pA/Hz1/2 and Sx1/2 = 0.5 pm/Hz1/2). We demonstrate f0 tuning by controlling gate voltage VG and achieve frequency tunability Δf0/f0 ≈ 8% and resonance frequency change Δf0/ΔVG ≈ 0.53 kHz/mV. This study helps pave the way to realizing ultrasensitive self-transducing 2D nanoelectromechanical systems at room temperature, in all-electronic configurations, for on-chip applications. 

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4. A 0.4–1.2 GHz SiGe Cryogenic LNA for Readout of MKID Arrays

   Hosseini, Mohsen; Wong, Wei-Ting; Bardin, Joseph (January 2019, 2019 IEEE/MTT-S International Microwave Symposium)

   The design and characterization of a low noise amplifier optimized for the readout of microwave kinetic inductance detectors is described. The work is first motivated through a description of microwave kinetic inductance detectors and a discussion of the requirements for the low-noise amplifiers employed for readout of these devices. Next, the design of a two-stage silicon germanium cryogenic integrated circuit low noise amplifier is presented. The small-signal and large-signal characteristics of the fabricated amplifier are then measured. It is shown that, at a physical temperature of 16 K, the amplifier achieves a gain of greater than 30 dB and an average noise temperature of 3.3 K over the 0.4–1.2 GHz frequency band while dissipating less than 7 mW. Moreover, the wideband compression characteristics are measured it is found that the linearity of the amplifier is sufficient to support frequency domain multiplexed readout of more than 500 detectors. 

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5. Ferroelectric transistor model based on self-consistent solution of 2D Poisson's, non-equilibrium Green's function and multi-domain Landau Khalatnikov equations

   https://doi.org/10.1109/IEDM.2017.8268385  

   Saha, A. K.; Sharma, P.; Dabo, I.; Datta, S.; Gupta, S. K. (December 2017, International Electron Device Meetings)

   We present a physics-based model for ferroelectric/negative capacitance transistors (FEFETs/ NCFETs) without an inter-layer metal between ferroelectric and dielectric in the gate stack. The model self-consistently solves 2D Poisson's equation, non-equilibrium Green's function (NEGF) based charge and transport equations, and multi-domain Landau Khalatnikov (LK) equations with the domain interaction term. The proposed simulation framework captures the variation of ferroelectric (FE) polarization (P) along the gate length due to non-uniform electric field (E) along the channel. To calibrate the LK equations, we fabricate and characterize 10nm HZO films. Based on the calibrated model, we analyze the gate/drain voltage dependence of P distribution in the FE and its effect on the channel potential and current-voltage characteristics. Our results highlight the importance of larger domain interaction to boost the benefits of FEFETs with subthreshold swing (SS) as small as ~50mV/decade achieved at room temperature. As domain interaction increases, the characteristics of FEFETs without inter-layer metal (SS, negative drain induced barrier lowering (DIBL), negative output conductance) approach those of FEFETs with inter-layer metal. 

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