Unity Current Gain Cutoff Frequency Research Articles

Effects of high-dose gamma-ray irradiation on an In0.53Ga0.47As high electron mobility transistor

We investigate the effects of gamma-ray (γ-ray) irradiation on an In0.53Ga0.47As high electron mobility transistor (HEMT). After γ-ray radiation, the irradiated HEMT shows degradation of the maximum transconductance (g m,max ), the unity current gain cutoff frequency (f T ), and the maximum oscillation frequency (f max)—about 12.8%, 18.0%, and 16.9%, respectively—because of an increase in on-resistance (Ron) in In0.53Ga0.47As HEMTs exposed to high-dose γ-ray radiation. Moreover, we obtain a minimum noise figure (NFmin) of about 1 dB from 8 to 40 GHz for the irradiated HEMT, which is a lower value compared to a non-irradiated HEMT; this is because the gate leakage current is reduced after γ-ray irradiation.

11.2 W/mm power density AlGaN/GaN high electron-mobility transistors on a GaN substrate

In this letter, high power density AlGaN/GaN high electron-mobility transistors (HEMTs) on a freestanding GaN substrate are reported. An asymmetric Γ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance. The breakdown voltage (BV) is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92 μm. A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V. The maximum oscillation frequency (f max) and unity current gain cut-off frequency (f t) of the AlGaN/GaN HEMTs exceed 30 and 20 GHz, respectively. The results demonstrate the potential of AlGaN/GaN HEMTs on free-standing GaN substrates for microwave power applications.

RF characteristics of 150‐nm AlGaN/GaN high electron mobility transistors fabricated using i‐line stepper lithography

AbstractThis article reports radio frequency characteristics of 150‐nm gate aluminum gallium nitride (AlGaN)/gallium nitride (GaN) high electron mobility transistors (HEMTs) fabricated using i‐line stepper lithography and a thermal reflow technique. The authors have developed two different gate structures that were a field‐plated gate using the lift‐off process and a Y‐shaped gate using the ion‐milling process. Fabricated HEMTs using these different gate structures exhibited nearly equivalent DC characteristics. The field‐plated gate device showed a unity current gain cutoff frequency (fT) of 35 GHz and a maximum oscillation frequency (fmax) of 106 GHz, while the Y‐shaped gate device showed fT of 36 GHz and fmax of 115 GHz. The equivalent circuit analysis indicated a decrease in the gate‐drain capacitance and the drain conductance is responsible for the improved fmax in the Y‐shaped gate device.

Heterogeneous and Monolithic 3D Integration Technology for Mixed-Signal ICs

For next-generation system-on-chips (SoCs) in diverse applications (RF, sensor, display, etc.) which require high-performance, small form factors, and low power consumption, heterogeneous and monolithic 3D (M3D) integration employing advanced Si CMOS technology has been intriguing. To realize the M3D-based systems, it is important to take into account the relationship between the top and bottom devices in terms of thermal budget, electrical coupling, and operability when using different materials and various processes during integration and sequential fabrication. In this paper, from this perspective, we present our recent progress of III-V devices on Si bottom devices/circuits for providing informative guidelines in RF and imaging devices. Successful fabrication of the high-performance InGaAs high electron mobility transistors (HEMTs) on the bottom ICs, with a high unity current gain cutoff frequency (fT) and unity power gain cutoff frequency (fMAX) was accomplished without substrate noise. Furthermore, the insertion of an intermediate metal plate between the top and bottom devices reduced the thermal interaction. Furthermore, the InGaAs photodetectors (PDs) were monolithically integrated on Si bottom devices without thermal damage due to low process temperature. Based on the integrated devices, we successfully evaluated the device scalability using sequential fabrication and basic readout functions of integrated circuits.

20.2 GHz‐µm fT–LG in InAlN/GaN‐on‐Si High Electron Mobility Transistors

Herein, InAlN/GaN‐on‐Si high‐electron‐mobility transistors (HEMTs) with an fT–LG product of 20.2 GHz–μm are demonstrated. The device with a gate length of 200 nm and a source–drain spacing of 900 nm exhibits a peak transconductance of 543 mS mm−1, an ION/IOFF ratio of ≈107, a maximum on‐current of 2.4 A mm−1, and an on‐resistance of 1.07 Ω mm. Small‐signal characteristics show a unity current gain cutoff frequency of 101 GHz. Delay time analysis is performed to evaluate various delay components and their contribution to the small‐signal performance of the device. An effective electron velocity of 1.56 × 107 cm s−1 is estimated in these devices, which minimizes the intrinsic delay of the transistor. The factors limiting the fT–LG product in deeply scaled devices are discussed using the delay analysis.

High-Frequency Operation of Vertical Organic Field-Effect Transistors.

The high‐frequency and low‐voltage operation of organic thin‐film transistors (OTFTs) is a key requirement for the commercial success of flexible electronics. Significant progress has been achieved in this regard by several research groups highlighting the potential of OTFTs to operate at several tens or even above 100 MHz. However, technology maturity, including scalability, integrability, and device reliability, is another crucial point for the semiconductor industry to bring OTFT‐based flexible electronics into mass production. These requirements are often not met by high‐frequency OTFTs reported in the literature as unconventional processes, such as shadow‐mask patterning or alignment with unrealistic tolerances for production, are used. Here, ultra‐short channel vertical organic field‐effect transistors (VOFETs) with a unity current gain cut‐off frequency (f T) up to 43.2 MHz (or 4.4 MHz V−1) operating below 10 V are shown. Using state‐of‐the‐art manufacturing techniques such as photolithography with reliable fabrication procedures, the integration of such devices down to the size of only 12 × 6 µm2 is shown, which is important for the adaption of this technology in high‐density circuits (e.g., display driving). The intrinsic channel transconductance is analyzed and demonstrates that the frequencies up to 430 MHz can be reached if the parasitic electrode overlap is minimized.

Heterogeneous and Monolithic 3D Integration of III-V-Based Radio Frequency Devices on Si CMOS Circuits.

Next-generation wireless communication such as sixth-generation (6G) and beyond is expected to require high-frequency, multifunctionality, and power-efficiency systems. A III-V compound semiconductor is a promising technology for high-frequency applications, and a Si complementary metal-oxide-semiconductor (CMOS) is the never-beaten technology for highly integrated digital circuits. To harness the advantages of these two technologies, monolithic integration of III-V and Si electronics is beneficial, so that there have been everlasting efforts to accomplish the monolithic integration. Considering that the on horizon 6G wireless communication requires faster and more energy-efficient system-on-chip technologies, it is imperative to realize a radio frequency (RF) system in which III-V technology and Si CMOS technology are integrated at a device level. Here we report heterogeneous and monolithic three-dimensional (3D) analog/RF-digital mixed-signal integrated circuits that contain two types of InGaAs high-electron-mobility transistors (HEMTs) designed for high fT and fMAX in the top and Si CMOS mixed-signal circuits consisting of an analog-to-digital converter and digital-to-analog converter in the bottom. A high unity current gain cutoff frequency of 448 GHz and unity power gain cutoff frequency of 742 GHz have been achieved by the fT oriented and fMAX oriented InGaAs HEMTs, respectively, without being affected by mixed-signal interference. At the same time, the bottom Si CMOS circuits provide valid signals without any performance degradation by the integration process.

High‐Current‐Density Enhancement‐Mode Ultrawide‐Bandgap AlGaN Channel Metal–Insulator–Semiconductor Heterojunction Field‐Effect Transistors with a Threshold Voltage of 5 V

Enhancement‐mode ultrawide‐bandgap Al0.65Ga0.35N/Al0.4Ga0.6N metal–insulator–semiconductor heterojunction field‐effect transistors are demonstrated using fluorine‐plasma treatment for threshold voltage control and Al2O3 as gate dielectric. The device exhibits a threshold voltage of 5 V, a maximum drain current density of 105 mA mm−1, and a transconductance of 19 mS mm−1. In addition, the capability to achieve low off‐state current density at 3–4 × 10−9 mA mm−1, an exceptionally low gate leakage current density of 1.4 × 10−8 mA mm−1 even at a high forward gate bias of VGS = 12 V, and a current on/off ratio >1010 is shown. Small signal measurement shows that the device has a unity current gain cutoff frequency fT of 3.8 GHz and power gain cutoff frequency fmax of 4.5 GHz.

Small signal analysis of ultra-wide bandgap Al0.7Ga0.3N channel MESFETs

We report RF small signal analysis of ultra-wide bandgap AlGaN channel MESFETs with Al composition of 70%. Ohmic contacts are achieved using a linearly-graded and heavily-doped AlGaN layer grown by metal organic chemical vapor deposition. The device with a gate length of 250 nm shows a drain current density (IDSS) of 370 mA/mm when the gate is shorted to source, unity current gain cutoff frequency (fT) of 8.8 GHz, and maximum oscillating frequency (fMAX) of 15 GHz. Bias-dependent device parameters are extracted from measured S-parameters based on a small-signal equivalent circuit model. The peak effective electron velocity of 2.9 × 106 cm/s is obtained at VGS = − 7 V. We show that the average electron velocity (ve) under the gate limits the device intrinsic RF performance while the high source access resistance (Rs) and drain access resistance (Rd) limits the device extrinsic RF performance.

Effects of periodic patterns in recessed ohmic contacts on InAlGaN/GaN heterostructures

Pattern-recessed ohmic contacts are investigated for InAlGaN/GaN high-electron-mobility transistors (HEMTs). Periodically-recessed patterns are introduced in the source and drain contact area to achieve the lower contact resistance by making sidewall contact as well as top contact on the active mesa. The lowest ohmic contact resistance (Rc) of 0.19 Ω·mm is achieved. It is significantly lower than the contact resistance of 0.29 Ω·mm, which is obtained from the conventional ohmic contact without recessed pattern. When the proposed ohmic contact scheme is introduced in 3-μm-long gate HEMTs, the on-resistance and the maximum transconductance are improved from 2.41 Ω·mm and 320 mS/mm to 2.24 Ω·mm and 332 mS/mm, respectively. The unity current gain cut-off frequency (fT) and the maximum oscillation frequency (fmax) of the device is increased from 2.78 and 10.05 GHz to 2.97 and 10.65 GHz, respectively.

Improved Drain Current Characteristics of Germanium Source Triple Material Double Gate Hetero-Dielectric Stacked TFET for Low Power Applications

In this paper a novel device structure of Triple Material Double Gate (TMDG) SiO2/High-k stacked (Hetero-Dielectric) Tunnel Field Effect Transistor (TFET) with germanium source has been proposed. Three different work function metals over the channel region act as a barrier in the channel which inturn restricts ambipolar effect. Also the concept of hetero-junction at the interface of source to channel region of the proposed device helps to improve the ION current characteristics. The parameters like surface potential, electric field, ION current and IOFF current of the hetero-junction TMDG hetero-dielectric stacked TFET device have been investigated in this work. The proposed device gives an improved ION current and better suppression in leakage current. From the presented results it is found that very low leakage current IOFF (approximately 10−17 A/mm), prominent enhancement in ION current (approximately 10−4 A/mm) and the ION/IOFF current ratio is 1013. Also there is a notable enhancement in ON and OFF current compared with the silicon based TMDG hetero dielectric TFET. The proposed device exhibit unity current-gain cut-off frequency of 50 GHz, while it is 37 GHz for silicon source TMDG hetero-dielectric stacked TFET. 10−17A/mm leakage current confirms the reduced power consumption and 10−4A/mm ON current confirms to speed up the charging and discharging of output capacitance. The results reveal that the germanium source (Hetero-junction) TM-DG Hetero-Dielectric TFET provides better result for Electric field, ION current, IOFF current and ION/IOFF current ratio than the silicon based TM-DG Hetero-Dielectric TFET. The novel proposed device is fitting for low power applications.

Enhancement of Performance in TFET by Reducing High-K Dielectric Length and Drain Electrode Thickness

A Dual Material Double Gate Tunnel Field Effect Transistor (DMDGTFET) with reduced high-K dielectric length (LK = 15 nm) and drain electrode thickness (6 nm) is proposed and performed a TCAD simulation. The simulation result of proposed device exhibits suppression in gate-to-drain capacitance (CGD). The (CGD) is proportional to dielectric constant (e) of the gate insulator and drain-electrode thickness of device. In the proposed DMDGTFET, the reduction in drain electrode thickness and LK gives a low electron concentration (Q) and low dielectric constant (e) in channel/drain junction, respectively, which results in suppression of CGD. At VGS = 2 V, the CGD for the proposed and conventional device are 9 f F, and 7 f F, respectively. In addition, the proposed device exhibit unity current-gain cut-off frequency of 62 GHz, while it is 57 GHz for conventional device. The on-current (ION) of the proposed device is also measured as 2 × 10−5 (A/mm). Thus, the proposed DMDGTFET is potential candidate for fast switching applications without compromising on-current (ION).

High performance dual-gate SiGe MOSFET for radio-frequency applications

In this paper, we propose a new Si0.6Ge0.4 n-channel dual-gate metal-oxide-semiconductor field-effect transistor (DGMOS) structure for high frequency small signal applications. The gate length of the device is 60 nm and gate-oxide (SiO2) thickness is 2 nm with n+ poly-silicon as gate material. Both the gates of DGMOS are placed in the oxide-filled trenches leading to formation of dual conduction channels which enhances the drive current, gain and frequency response. Two-dimensional simulation tool (ATLAS) is used to analyse and compare the performance of the proposed structure with conventional device. The DGMOS provides 5.35 times higher current drivability, 306% improvement in peak transconductance, 114% enhancement in unity current gain cut-off frequency and 3.75 times higher oscillation frequency with good control of short channel effects in comparison to the conventional MOSFET.

Improved RF and DC performance in AlGaN/GaN HEMT by P-type doping in GaN buffer for millimetre-wave applications

In this paper, the RF and DC performance of AlGaN/GaN HEMT having p-type doping in GaN buffer layer was analysed. Novelty of this work lies in the inclusion of P-type doping in GaN buffer of proposed GaN-HEMT. The result shows the significance of p-type doping at GaN buffer layer for enhancing the RF characteristics of the AlGaN/GaN HEMT. The use of p-type doping in GaN buffer layer increase the conduction band minima in the channel and thereby improving the transconductance of the device. The proposed HEMT achieves a peak transconductance of 330 mS/mm at VGS = −2 V and a maximum drain current of 850 mA/mm. The unity-gain cut-off frequency, small signal capacitance and conductance were also extracted to demonstrate its influence on RF performance. The proposed GaN HEMT has exhibited a unity current gain cut-off frequency of 45 GHz, which is 40% higher than that of conventional HEMT. The improved RF and DC performance of proposed HEMT makes it suitable for millimetre-wave applications.

Ultra-Wide Bandgap AlxGa1-xN Channel Transistors

High Al-composition AlxGa1-xN, an emerging class of materials, is gaining significant traction due to its high critical breakdown electric field exceeding that of GaN and high electron saturation velocity that is comparable to GaN. High Al-composition AlxGa1-xN holds promise for applications such as highly scaled next generation RF devices and power devices. However, significant strides remain to be made before AlxGa1-xN can take a share of the limelight. Encouraging progress has been made in recent years, including multiple reports of RF operation of AlxGa1-xN channel transistors with reported unity current gain cutoff frequency as high as 40 GHz, high current density devices with the maximum reported current density exceeding 600 mA/mm and reports of breakdown fields in lateral transistors that are almost 3× the reported breakdown field for GaN channel devices of similar dimensions. This paper focuses on the lateral devices demonstrated thus far and discusses breakthrough performance results achieved for AlxGa1-xN channel transistors together with the key challenges that are yet to be properly addressed. The paper starts with a discussion of contact formation to AlxGa1-xN films – the key difficulty of fabricating AlxGa1-xN transistors. This is followed by a discussion of the types of devices that are typically used. This is followed up with a discussion of the approach required to make high quality devices with AlxGa1-xN as a template together with some recent result highlights.

A Pulse-Biasing Small-Signal Measurement Technique Enabling 40\u2009MHz Operation of Vertical Organic Transistors

Organic/polymer transistors can enable the fabrication of large-area flexible circuits. However, these devices are inherently temperature sensitive due to the strong temperature dependence of charge carrier mobility, suffer from low thermal conductivity of plastic substrates, and are slow due to the low mobility and long channel length (L). Here we report a new, advanced characterization circuit that within around ten microseconds simultaneously applies an accurate large-signal pulse bias and a small-signal sinusoidal excitation to the transistor and measures many high-frequency parameters. This significantly reduces the self-heating and therefore provides data at a known junction temperature more accurate for fitting model parameters to the results, enables small-signal characterization over >10 times wider bias I–V range, with ~105 times less bias-stress effects. Fully thermally-evaporated vertical permeable-base transistors with physical L = 200 nm fabricated using C60 fullerene semiconductor are characterized. Intrinsic gain up to 35 dB, and record transit frequency (unity current-gain cutoff frequency, fT) of 40 MHz at 8.6 V are achieved. Interestingly, no saturation in fT − I and transconductance (gm − I) is observed at high currents. This paves the way for the integration of high-frequency functionalities into organic circuits, such as long-distance wireless communication and switching power converters.

Effects of Gate-Length Scaling on Microwave MOSFET Performance

This paper focuses on the extraction of an accurate small-signal equivalent circuit for metal-oxide-semiconductor field-effect transistors (MOSFETs). An analytical modeling approach was developed and successfully validated through the comparison between measured and simulated scattering parameters. The extraction of the equivalent circuit elements allowed for the estimation of the intrinsic unity current-gain cutoff frequency, which is a crucial figure of merit for assessing the high-frequency performance. The experimental data show that the cutoff frequency of the tested devices exhibits a nearly ideal scaling behavior with decreasing gate length.

Graphene Klein tunnel transistors for high speed analog RF applications

We propose Graphene Klein tunnel transistors (GKTFET) as a way to enforce current saturation while maintaining large mobility for high speed radio frequency (RF) applications. The GKTFET consists of a sequence of angled graphene p-n junctions (GPNJs). Klein tunneling creates a collimation of electrons across each GPNJ, so that the lack of substantial overlap between transmission lobes across successive junctions creates a gate-tunable transport gap without significantly compromising the on-current. Electron scattering at the device edge tends to bleed parasitic states into the gap, but the resulting pseudogap is still sufficient to create a saturated output (ID–VD) characteristic and a high output resistance. The modulated density of states generates a higher transconductance (gm) and unity current gain cut-off frequency (fT) than GFETs. More significantly the high output resistance makes the unity power gain cut-off frequency (fmax) of GKTFETs considerably larger than GFETs, making analog GKTFET potentially useful for RF electronics. Our estimation shows the fT/fmax of a GKTFET with 1 μm channel reaches 33 GHz/17 GHz, and scale up to 350 GHz/53 GHz for 100 nm channel (assuming a single, scalable trapezoidal gate). The fmax of a GKTFET is 10 times higher than a GFET with the same channel length.

Comparisons between Dual and Tri Material Gate on a 32 nm Double Gate MOSFET

The paper reports a comparative analysis between the dual material gate double gate (DMG-DG) nMOSFET and the tri material gate double gate (TMG-DG) nMOSFET in terms of their analog and RF performance. Three different devices having the DMG-DG structure have been considered. Each of the devices have different higher workfunction material gate length (L1) to lower workfunction material gate length (L2) ratio (L1:L2). Along with the three devices, the performance of the TMG-DG nMOSFET is compared. The analog parameters considered for the comparison are the drain current ([Formula: see text]), the transconductance ([Formula: see text]), the transconductance generation factor ([Formula: see text]/[Formula: see text]) and the intrinsic gain ([Formula: see text]Ro). The drain induced barrier lowering (DIBL) of the devices is compared. The RF analysis is performed using the non quasi static (NQS) approach. We consider the intrinsic gate to source capacitances ([Formula: see text]), the intrinsic gate to drain capacitance ([Formula: see text]), the intrinsic gate to source resistances ([Formula: see text]), the intrinsic gate to drain resistance ([Formula: see text]), the transport delay ([Formula: see text]), the unity current gain cut-off frequency ([Formula: see text]) and the max frequency of oscillation ([Formula: see text]) for the RF comparisons. A single stage amplifier is also implemented using the devices for a circuit comparison.

Impact of Asymmetric Dual-k Spacer in the Underlap Regions of Sub 20 nm NMOSFET with Gate Stack

This paper shows the systematic study of underlap double gate (U-DG) NMOSFETs with Gate Stack (GS) under the influence of dual-k spacers at the different underlap regions. In highly scaled devices, underlap is used at the Source and Drain side so as to reduce the short channel effects (SCE's) but at the cost of low on current (ION) and increased channel resistance. The high-k spacers are used to counter this problem. The ION is improved but at the cost of highly enhanced parasitic capacitances. This paper explores the possibility of using asymmetric dual-k spacer at the source underlap side so as to counter the shortcomings of high-k spacers in highly scaled devices on the basis of analog parameters: ION, gm, gm/ID, and intrinsic gain, gmRo and RF performance in terms of parasitic gate capacitance (Cgs, Cgd and Cgg),gate to source/drain resistances (Rgs and Rgd), transport delay (τm), the unity current gain cut-off frequency (fT) and the maximum frequency of oscillation (fmax). A single stage amplifier performance is also analyzed where it has been seen that the asymmetric dual-k spacer at the source underlap side gives better performance as compared to the other devices under comparison.