Device Bias Conditions Research Articles

Analysis of thermal noise characteristics in 10 nm metal oxide semiconductor field effect transistor

<sec>Small size metal-oxide-semiconductor field effect transistor (MOSFET), owing to their high theoretical efficiency and low production cost, have received much attention and are at the frontier of transistors. At present, their development is bottlenecked by physical limits due to equal scaling down of devices, which requires further improvement in terms of materials choice and device fabrication. As the MOSFET devices scale down to nanometer scale, on the one hand, the resulting short channel effect affects severely the thermal noise property; on the other hand, it makes the ratio of thermal noise in the gate, source, drain and substrate regions become higher and higher. However, the traditional thermal noise model mainly considers thermal noise of large-size devices, and its model does not consider the channel saturation region. In view of this, it is necessary to establish a small size MOSFET thermal noise model and analyze its characteristics.</sec><sec>At present, there are some researches on MOSFET thermal noise, but they mainly focus on the thermal noise in channel region of large size nanoscale MOSFET. In the present work, according to the device structure and inherent thermal noise characteristics, we establish a thermal noise model for MOSFETs of 10 nm feature size. The model includes contributions of substrate region, gate-source-drain region, and channel region. In the channel region is also included the thermal noise related to the device saturation regime. Using such a model, the dependence of channel thermal noise and total thermal noise on the device bias condition and device parameters are investigated, evidencing the existence of thermal noise in the device saturation regime, which are consistent with the experimental results in the literature. The thermal noise increases with the gate voltage and source-drain voltage rising as the device structure shrinks. In a temperature range of 100–400 K, the thermal noise is basically on the order of 10<sup>21</sup>, indicating that the temperature has a great influence on the thermal noise. The thermal noise model established in this work can be applied to analyzing the noise performances of small size MOSFET devices, and the conclusions drawn from the present study are beneficial to improving the efficiency, lifetime, and response speed of MOSFETs on a nanometer scale.</sec>

Light sources with bias tunable spectrum based on van der Waals interface transistors

Light-emitting electronic devices are ubiquitous in key areas of current technology, such as data communications, solid-state lighting, displays, and optical interconnects. Controlling the spectrum of the emitted light electrically, by simply acting on the device bias conditions, is an important goal with potential technological repercussions. However, identifying a material platform enabling broad electrical tuning of the spectrum of electroluminescent devices remains challenging. Here, we propose light-emitting field-effect transistors based on van der Waals interfaces of atomically thin semiconductors as a promising class of devices to achieve this goal. We demonstrate that large spectral changes in room-temperature electroluminescence can be controlled both at the device assembly stage –by suitably selecting the material forming the interfaces– and on-chip, by changing the bias to modify the device operation point. Even though the precise relation between device bias and kinetics of the radiative transitions remains to be understood, our experiments show that the physical mechanism responsible for light emission is robust, making these devices compatible with simple large areas device production methods.

Experimental Investigation of Thermal Actuation Crosstalk in Phase-Change RF Switches Using Transient Thermoreflectance Imaging

This article reports an experimental investigation of transient heat distribution and thermal actuation crosstalk in phase-change material (PCM) germanium telluride (GeTe)-based radio frequency (RF) switches. The RF switches are designed and optimized for efficient thermal energy transport from the embedded microheater to the PCM. Various multiport miniaturized monolithically integrated complex RF components require several switches to be integrated extremely close to each other. Thermal crosstalk is crucial in multiport complex devices to ensure that individual tuning elements actuate independently without influencing nearby switches’ performance. Thermal cross section simulations are performed using multiphysics finite-element modeling (FEM) to optimize the heat distribution within the PCM channel and are experimentally validated via transient thermoreflectance imaging technique with ultrafast temporal and spatial resolution. The devices are fabricated in-house using a custom eight-layer microfabrication process. The optimum device bias conditions, melt-quench sequence, and thermal actuation crosstalk limits are experimentally validated to develop miniaturized monolithic densely packed complex reconfigurable phase-change circuits. It is the first-ever demonstration of experimental transient thermal insights on phase-change RF switches.

Velocity overshoot decay mechanisms in compound semiconductor field-effect transistors with a submicron characteristic length

Velocity overshoot is a critically important nonstationary effect utilized for the enhanced performance of submicron field-effect devices fabricated with high-electron-mobility compound semiconductors. However, the physical mechanisms of velocity overshoot decay dynamics in the devices are not known in detail. Therefore, a numerical analysis is conducted typically for a submicron GaAs metal-semiconductor field-effect transistor in order to elucidate the physical mechanisms. It is found that there exist three different mechanisms, depending on device bias conditions. Specifically, at large drain biases corresponding to the saturation drain current (dc) region, the velocity overshoot suddenly begins to drop very sensitively due to the onset of a rapid decrease of the momentum relaxation time, not the mobility, arising from the effect of velocity-randomizing intervalley scattering. It then continues to drop rapidly and decays completely by severe mobility reduction due to intervalley scattering. On the other hand, at small drain biases corresponding to the linear dc region, the velocity overshoot suddenly begins to drop very sensitively due to the onset of a rapid increase of thermal energy diffusion by electrons in the channel of the gate. It then continues to drop rapidly for a certain channel distance due to the increasing thermal energy diffusion effect, and later completely decays by a sharply decreasing electric field. Moreover, at drain biases close to a dc saturation voltage, the mechanism is a mixture of the above two bias conditions. It is suggested that a large secondary-valley energy separation is essential to increase the performance of submicron devices.

Bias Dependence of Total Ionizing Dose Effects in SiGe-MOS FinFETs<formula formulatype="inline"> <tex Notation="TeX"/> </formula>

The total ionizing dose (TID) response of double-gate SiGe- SiO 2 /HfO 2 pMOS FinFET devices is investigated under different device bias conditions. Negative bias irradiation leads to the worst-case degradation due to increased hole trapping in the HfO 2 layer, in contrast to what is typically observed for devices with SiO 2 or HfO 2 gate dielectrics. This occurs in the devices because radiation-induced holes that are generated in the SiO 2 interfacial layer can transport and become trapped in the HfO 2 under negative bias, leading to a more negative threshold voltage shift than observed at 0 V bias. Similarly, radiation-induced electrons that are generated in the SiO 2 interfacial layer can transport into the HfO 2 and become trapped under positive bias, leading to a more positive threshold voltage shift than observed at 0 V bias.

Suppression of microwave rectification effects in electrically detected magnetic resonance measurements

Spin-dependent transport properties of micro- and nano-scale electronic devices are commonly studied by electrically detected magnetic resonance (EDMR). However, the applied microwave fields in EDMR experiments can induce large rectification effects and result in perturbations of the device bias conditions and excessive noise in the EDMR spectra. Here we examine rectification effects of silicon metal-oxide-semiconductor field-effect transistors exposed to X-band microwave irradiation and show that the rectification effects can be effectively suppressed by incorporating a global capacitive shunt covering the device. We demonstrate that the signal-to-noise ratio in the EDMR spectra improves by over a factor of ten in the shunted devices.

Linearity Characterization and Optimization of Millimeter-Wave GaN HEMTs

This paper presents the first comprehensive study of the linearity characteristics of GaN/SiC high-electron mobility transistors (HEMTs) at millimeter-wave (mmW). Similar size devices from three sources are compared using AM-AM, AM-PM, two-tone, and 16-quadrature-amplitude modulation (16QAM) modulated waveforms measurements at 31.5 GHz. Additionally, error vector magnitude (EVM) and spectrum regrowth [adjacent channel power ratio (ACPR)] data are also presented. The results were measured, using a unique digital waveform system integrated with a mmW (50-GHz) load-pull system, for HEMTs at different classes of operation: A, AB, and B. In all devices, it is observed that a “balanced AB” (b-AB) class of device bias condition where linearity and efficiency are simultaneously optimized. A linearity figure of merit FOM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">linearity</sub> , based on single-tone power measurements, is defined and calculated for each class. The FOM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">linearity</sub> closely correlates with linearity performance of the HEMT under two-tone and digitally modulated drive conditions. Compared with class A, at a fixed output power, a b-AB class showed a 5-10-dB improvement in intermodulation distortions, combined with 1.2 × to 1.9 × enhancement in drain efficiency. The characterization methodology and derived FOM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">linearity</sub> should benefit monolithic microwave integrated circuit (MMIC) designers to optimize the operation of GaN HEMTs. The results also indicate that GaN HEMTs can provide linearity characteristics suitable for applications such as satellite communications, while maintaining high efficiency and power density.

Switch-on overshoot transient decay mechanism in polycrystalline silicon thin-film transistors

The present work investigates the switch-on transient decay in polycrystalline thin-film transistors. The decay is found to follow the stretched exponential relaxation model independently of the polycrystalline film properties and the device bias conditions or operating temperature. The temperature dependence of the stretched exponential relaxation allows for the determination of the decay time and, furthermore, the process activation energy.

Charge-collection dynamics of InP-based high electron mobility transistors (HEMTs)

Time-resolved charge-collection measurements are performed on InAlAs/InGaAs HEMTs with pulsed laser excitation as a function of device bias conditions and the incident laser pulse energy. The results provide clear evidence for the presence of charge-enhancement processes that, in many ways, are analogous to those observed previously for GaAs FET technology.

Present State of the Surface Potential Measurements by Kelvin Force Microscopy. Potential Measurement of Si Nano-structures by Kelvin Probe Force Microscopy.

Surface potential measurements of Si nano-structures by KFM (Kelvin probe force microscopy) are reviewed from a viewpoint of device research. For the development of sub-0.1 µm MOSFETs and future novel devices like dot-based single-electron tunneling transistors, it is most important to know the internal potential distribution of devices. In this review, first, the most fundamental structure of p-n junction formed on Si surface is described. It is noted that an unexpectedly small potential difference across the p-n junction was detected. The surface band bending due to the trapped charge would probably be responsible for almost flat profiles. Next, the potential distribution in the surface channel region of MOSFET-like structure on SOI (silicon-on-insulator) substrates is shown under several device-bias conditions. Finally, it is shown that Si quantum dot is recognized in KFM images after charge-injection process by generation of a small but significant potential difference at the dot site. These results indicate that KFM is undoubtedly useful in detecting potential distributions of device surfaces with or without device-driving voltage sources.

Charge-collection characteristics of low-power ultrahigh speed, metamorphic AlSb/InAs high-electron mobility transistors (HEMTs)

Time-resolved charge-collection measurements are performed on AlSb/InAs HEMTs with pulsed laser excitation as a function of device bias conditions and the incident laser pulse energy. The results provide clear evidence for the presence of charge-enhancement processes that, in many ways, are analogous to those observed previously for GaAs FET technology.

Study of neutron damage in GaAs MESFETs

Implanted channel GaAs MESFETs subjected to neutron irradiation show large modifications of the pinch-off voltage, open-channel saturation current, and transconductance in agreement with previous results. In this work we demonstrate how an experimental technique, based on the frequency dispersion of the transconductance, g/sub m/(f), and output conductance, g/sub D/(f), can identify the deep levels induced by neutron irradiation through measurements performed directly on packaged devices. After irradiation, a frequency dispersion of the transconductance has been observed, while it was flat in the unirradiated device. The g/sub m/(f) curve shape depends on the device bias conditions, and it has permitted for the first time to evaluate the activation energy of different deep levels induced by neutron irradiation in MESFETs.

Understanding linearity in wireless communication amplifiers

This paper investigates the linearity of active devices and amplifiers that have modulated input signals. We describe an implementation of a mathematical technique for calculating spectral regrowth due to the nonlinear amplification of modulated signals typically used in wireless communication systems. This technique only requires knowledge of the single-tone gain and phase data as a function of input power and can be applied to any modulated signal given (a) the device or amplifier characteristics do not change significantly over the bandwidth of the input signal and (b) the modulation frequencies are much less than the carrier frequency. Verification of the mathematical technique is presented using examples of measured and calculated spectra for /spl pi//4-differential quadrature phase shift keying (DQPSK) personal handy phone system (PHS) and code division multiple access (CDMA) Offset-QPSK personal communication system (PCS) modulation schemes. This calculation technique is essential in determining fundamental tradeoffs between device performance (linearity, output power, gain, and power-added efficiency) and device bias conditions and load impedance.

Charge-collection characteristics of GaAs heterostructure FETs fabricated with a low-temperature grown GaAs buffer layer

The charge-collection characteristics of GaAs heterojunction-insulated-gate FETs fabricated with a low-temperature grown GaAs (LT GaAs) buffer layer are investigated as a function of device bias conditions for laser and ion irradiation. In accordance with earlier measurements, the LT GaAs FETs of this study exhibit a significant reduction in charge-collection efficiencies when compared to those of conventional FETs. This reduction in collected charge is associated with the efficient reduction of charge-enhancement mechanisms in the LT GaAs devices. It is revealed that charge-enhancement processes do occur in the LT devices under certain bias conditions, although at significantly reduced levels when compared to conventional FETs.

Picosecond charge-collection dynamics in GaAs MESFETs (for space application)

Ion and picosecond laser induced charge-collection measurements performed as a function of temperature and device bias conditions reveal the significant changes that occur in the charge collection transients as a function of these parameters. The temperature-dependent results provide new evidence that above-bandgap picosecond laser excitation can reproduce the primary features of the ion induced charge-collection transients measured for GaAs MESFETs. Bias dependence results reveal clearly the sensitive role of the device operating point in determining both the shape and the total integrated intensity of the measured charge-collection transients. Preliminary two-dimensional computer simulation results are presented which suggest carrier-induced channel modulation as the primary mechanism for enhanced charge collection in GaAs MESFETs. >