Xiao Sun

Study of gate oxide traps in HfO2/AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors by use of ac transconductance method

We introduce an ac-transconductance method to profile the gate oxide traps in a HfO2 gated AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistors (MOS-HEMTs) that can exchange carriers with metal gates, which in turn causes changes in analog and pulsed channel currents. The method extracts energy and spacial distributions of the oxide and interface traps under the gate from the frequency dependence of ac transconductance. We demonstrate the method using MOS-HEMTs with gate oxides that were annealed at different temperatures.

AC Transconductance Dispersion (ACGD): A Method to Profile Oxide Traps in MOSFETs Without Body Contact

We introduce an ac transconductance dispersion method (ACGD) to profile the oxide traps in an MOSFET without needing a body contact. The method extracts the spatial distribution of oxide traps from the frequency dependence of transconductance, which is attributed to charge trapping as modulated by an ac gate voltage. The results from this method have been verified by the use of the multifrequency charge pumping (MFCP) technique. In fact, this method complements the MFCP technique in terms of the trap depth that each method is capable of probing. We will demonstrate the method with InP passivated InGaAs substrates, along with electrically stressed Si N-MOSFETs.

Total-Ionizing-Dose Radiation Effects in AlGaN/GaN HEMTs and MOS-HEMTs

We have investigated the total ionizing dose (TID) radiation effects in AlGaN/GaN MOS-HEMTs as a function of dose and radiation bias, and compared them with conventional HEMTs. Under 10 keV X-ray irradiation, two distinct regimes of threshold voltage (V_th) shifts have been revealed: a rapid V_th shift at low doses for both HEMTs and MOS-HEMTs, and an additional V_th shift only found in MOS-HEMTs for doses up to at least 2 Mrad (SiO₂). The rapid V_th shift anneals quickly and is a strong function of layer material. We attribute this portion of the V_th shift to hole trapping in the AlGaN barrier layer. The V_th shift at high doses found only in MOS-HEMTs is attributed to hole trapping in the gate oxide. By comparing MOSFETs with HfO₂ and Al₂O₃ gate dielectrics that are annealed during processing at various temperatures, we find that 500^°C annealed HfO₂ shows the most promising TID response.

AC transconductance: A novel method to characterize oxide traps in advanced FETs without a body contact

A novel ac transconductance method for oxide trap characterization is introduced, validated and demonstrated on two advanced FETs without a body contact, including Si Ultra-Thin-Body and BOX (UTBB) Fully Depleted (FD) SOI MOSFETs and InGaAs MOSFETs. The proposed method can extract the energy and spatial distributions of oxide traps in a variety of device structures, gate areas, and channel materials.

Improved AC conductance and Gray-Brown methods to characterize fast and slow traps in Ge metal–oxide–semiconductor capacitors

We use an improved AC conductance method and a modified Gray-Brown method to study fast interface traps and slow border traps in Ge-based MOS capacitors. The combined methods provide the corrected Fermi energy level (E) versus gate voltage (Vg) relationship, even in samples with high densities of traps that cause significant C-V distortion, the energy distribution of interface traps, their capture cross sections (σ), as well as slow border traps. A wide range of σ’s in p-type Ge is found, indicating that there is more than one type of interface trap near the Ge valence band edge. In contrast, a constant σ near the Ge conduction band edge is observed in n-type Ge. XPS results indicate that Ge suboxides near the interface are accountable for the detected slow border traps.

Effect of H on interface properties of Al2O3/In0.53Ga0.47As

We report that depositing Al2O3 on InGaAs in an H-containing ambient (e.g., in forming gas) results in significant reduction of interface-trap density and significantly suppressed frequency dispersion of accumulation capacitance. The results of the inelastic electron tunneling spectroscopy study reveal that strong trap features at the Al2O3/InGaAs interface in the InGaAs band gap are largely removed by depositing Al2O3 in an H-containing ambient. Transmission electron microscopy images and x-ray photoelectron spectroscopy data shed some light on the role of hydrogen in improving interface properties of the Al2O3/In0.53Ga0.47As gate stack.

Total Ionizing Dose (TID) Effects in Extremely Scaled Ultra-Thin Channel Nanowire (NW) Gate-All-Around (GAA) InGaAs MOSFETs

InGaAs nanowire (NW) gate-all-around (GAA) MOSFETs exhibit superior radiation hardness compared to planar devices and FinFETs, benefitting from reduced gate-oxide electric fields. Applied gate bias during irradiation, channel thickness, and presence or absence of a forming gas anneal can strongly affect NW device radiation hardness. Low-frequency noise measurements are carried out to probe near-interfacial oxide-trap (border-trap) densities, and TCAD simulations are performed to assist in understanding the charge trapping in NW channel devices with high-k gate dielectrics. Optimized device structures exhibit high radiation tolerance.

Total Ionizing Dose Radiation Effects in Al 2 O

We have investigated total ionizing dose (TID) radiation effects in Al2O3-gated ultra-thin body In0.7Ga0.3 As MOSFETs. A non-monotonic dependence of the threshold voltage (Vth) on the X-ray radiation dose was observed and analyzed; the accompanying degradation in subthreshold swing (SS) likely is caused by non-uniform trapped charge in the near-interfacial Al2O3 rather than interface-trap generation. The off-current and gate breakdown voltage were independent of dose up to 6 Mrad(SiO2). Compared to the InP-free device, the device with an InP barrier is more vulnerable to TID effects in terms of Vth shift, SS, and mobility degradation.

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The impact of fluorine treatment on AlGaN/GaN MOS-HEMTs has been investigated. Fluorine was found to suppress pre-existing traps in MOS-HEMT, which improves the off-state at high temperatures. Fluorine doping and associated etching, however, also generates slow border traps and fast interface states that degrade the MOS-HEMT performance. Multi-faceted mechanisms for drain current degradation due to F-doping and gate-recess-etch have been investigated in enhancement-mode MOS-HEMTs.

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We report the properties of a MANAS (Metal/Al₂O₃/Nitride/Al₂O₃/Si) charge-trap memory cell structure, in which both the tunnel and the blocking dielectrics are made of high-quality Al₂O₃ deposited by the molecular-atomic-deposition (MAD) technique. Compared with state-of-the-art MANOS (Metal/Al₂O₃/Nitride/SiO₂/Si) and its derivatives, the MANAS structure features the following: 1) low-voltage/high-speed operation; 2) fabrication simplicity; and 3) high-temperature retention up to 250°C. These superb features of the MANAS memory cell structure can be attributed to the nearly trap-free nature of the MAD_Al₂O₃, as well as its relatively high conduction band offset and low valence band offset.