Power Field Effect Transistors Research Articles

Ultrathin Sn-doped Ga2O3 for power field-effect transistors: Si-compatible 4-inch array with high-k gate dielectric

Ultrathin Sn-doped Ga2O3 for power field-effect transistors: Si-compatible 4-inch array with high-k gate dielectric

Diamond Electronics and Related Wideband Gap Semiconductors for High Temperature Applications

This presentation is focused on understanding the basic science of two-dimensional carrier systems in diamond-based semiconductor electronics. Over the course of the presentation, we will present the following: • Process technology for diamond power field effect transistors (FETs) based on two-dimensional (2D) carrier transport in subsurface boron delta-doped structures • The theory of carrier transport in diamond FETs with 2D conducting channels • The results from materials and defect characterization techniques to locate, characterize, and monitor radiation-induced defects in these structures over various timescales • New research directions in applying 2D conduction channels to ultra-wide bandgap semiconductor transistors based on diamond materials as well as related wide band gap semiconductors, • Understand the dominant failure mechanisms operative in diamond-based FETs exposed to ionizing and non-ionizing radiation.

High mobility hydrogen-terminated diamond FET with h-BN gate dielectric using pickup method

Hydrogen-terminated diamond surfaces, emerging as a promising two-dimensional (2D) electron platform with great thermal and electronic properties, hold great potential for the next-generation high power and high frequency field effect transistor (FET). However, ideal gate dielectrics with high crystallinity and defect-free surfaces are still largely elusive. In this work, using the contamination-free pickup transfer method, hexagonal boron nitride (h-BN) flakes were fabricated on top of the hydrogen-terminated diamond surface to serve as a gate material and the passivation layer. The morphological and optical characterizations revealed the formation of homogeneous and intimate interface between h-BN and diamond. Benefiting from the h-BN gate dielectric layer, the maximum drain current density, subthreshold swing, and on/off ratio of diamond FET are measured to be −210.3 mA mm−1, 161 mV/dec, and 106, respectively. Especially, the transport measurement shows an almost constant Hall mobility of around 260 cm2 V−1 s−1 in the hole density range of 2 − 6 × 1012 cm−2, suggesting the excellent gate controllability of h-BN. Our results indicate that h-BN could form high-quality interface with hydrogen-terminated diamond, paving the way for the development of diamond-based electronic applications.

Optimisation of trench filling in GaN towards vertical HEMT structures

In this work we present studies how to fill epitaxially trenches in a GaN layer in order to form a current aperture for use in 3D high power field effect transistors. By optimising various growth parameters in our metal organic vapour phase epitaxy, we achieved an almost complete and smooth filling of 5 μm wide and 500 nm deep trenches etched into a GaN:Mg layer by reactive-ion etching. By using GaN:Si marker layers, the filling process could be excellently monitored. Eventually, a high electron mobility transistor structure was deposited on top of the optimized structures enabling an electrical assessment of this process.

An enhanced two-dimensional hole gas (2DHG) C\u2013H diamond with positive surface charge model for advanced normally-off MOSFET devices

Though the complementary power field effect transistors (FETs), e.g., metal–oxide–semiconductor-FETs (MOSFETs) based on wide bandgap materials, enable low switching losses and on-resistance, p-channel FETs are not feasible in any wide bandgap material other than diamond. In this paper, we propose the first work to investigate the impact of fixed positive surface charge density on achieving normally-off and controlling threshold voltage operation obtained on p-channel two-dimensional hole gas (2DHG) hydrogen-terminated (C-H) diamond FET using nitrogen doping in the diamond substrate. In general, a p-channel diamond MOSFET demonstrates the normally-on operation, but the normally-off operation is also a critical requirement of the feasible electronic power devices in terms of safety operation. The characteristics of the C–H diamond MOSFET have been analyzed with the two demonstrated charge sheet models using the two-dimensional Silvaco Atlas TCAD. It shows that the fixed-Fermi level in the bulk diamond is 1.7 eV (donor level) from the conduction band minimum. However, the upward band bending has been obtained at Al2O3/SiO2/C-H diamond interface indicating the presence of inversion layer without gate voltage. The fixed negative charge model exhibits a strong inversion layer for normally-on FET operation, while the fixed positive charge model shows a weak inversion for normally-off operation. The maximum current density of a fixed positive interface charge model of the Al2O3/C-H diamond device is − 290 mA/mm, which corresponds to that of expermental result of Al2O3/SiO2/C-H diamond − 305 mA/mm at a gate-source voltage of − 40 V. Also, the threshold voltage Vth is relatively high at Vth = − 3.5 V, i.e., the positive charge model can reproduce the normally-off operation. Moreover, we also demonstrate that the Vth and transconductance gm correspond to those of the experimental work.

Enabling Resonant Commutated Pole in Parallel Power FET Bridge Legs

To meet the requirements of higher current ratings and lower thermal impedances, paralleling power field-effect transistor (FET) discretes or modules is often a cost-effective or even an unavoidable solution. While paralleling FETs allows for a significant reduction in conduction loss, the switching loss is increased in hard-switching applications. This article proposes a generic soft-switching modulation scheme for parallel power FET bridge legs. Part of the paralleled FET legs is chosen as an auxiliary leg that is turned on prior to the remaining main legs. A resonant commutated pole (RCP) mode is then created, which enables the high-side FET of the auxiliary leg to achieve zero-current switching (ZCS) or quasi-ZCS and the remaining FETs to achieve zero-voltage switching. Thus, we can significantly reduce the switching loss that normally dominates the total power loss of high-frequency hard-switching converters particularly at partial and light loads. Experimental results from three parallel GaN high-electron-mobility transistor legs validate the effectiveness of this RCP-enabled solution in reducing switching losses and improving power conversion efficiencies. This article is accompanied by supplementary JIF and PDF files demonstrating the operational details of the RCP mode.

A review on emerging negative capacitance field effect transistor for low power electronics

Power consumption is the major concern for conventional CMOS based integrated circuit and systems. Since there is a scope of lowering supply voltage with steep-subthreshold swing field effect transistor (FET) devices, it has been advocated as a suitable candidate for future highly energy-efficient circuits and systems. Among all the developed and proposed low power FET devices, that possess subthreshold swing (SS) lesser than 60 mV/decade, the negative-capacitance FETs (NCFETs) have gained the major attention of scientific and academic communities. The concept of negative capacitance (NC) in FET is basically belongs to the amplify the internal potential without modification of transport phenomena. With this capability, the NCFET have achieved similar switching at lower supply voltage, VDD as compared to conventional MOSFETs. Property of achieving similar on-current (ION) lower off-current (IOFF) at lower supply voltage indicates that NCFETs help to reduce the power consumption and switching voltage. This can be achieved by slight modification of conventional CMOS devices by adding thin layer of ferroelectric (FE) layer in gate stack. This slight modification in conventional MOSFET is for the NC, which is a special feature of FE materials. FE materials having nonlinear dielectric behavior. This material has preexisting, which is switched in reverse direction when an external electric field is applied. In this paper, a detailed review of NCFET device has discussed and also compared with the Tunnel FET (TFET) and conventional MOSFET.

Pulsed techniques for the characterization of low-frequency dispersive effects in RF power FETs using a flexible measurement set-up

This work describes an on-wafer measurement architecture tailored to the broadband pulsed characterization of radio-frequency (RF) power field-effect transistors (FETs). Based on a 50-Ω environment and corresponding wave-variable domain representation, the set-up exploits the impedance matching and the broadband feature of its components, together with a full-bandwidth calibration, for the synthesis and measurement of pulsed waveforms with short pulse rise/fall times in the order of a few ns, while guaranteeing a reduced risk of oscillations.These measurement capabilities are particularly suited for experimentally assessing the FET performance reduction due to low-frequency dispersive effects caused by thermal and charge trapping phenomena. The flexibility of the set-up is showcased by discussing experimental examples of different measurement techniques in the kHz-to-GHz range, including single- and double-pulsed I–V characteristics and S-parameters, as well as pulsed continuous-wave (CW) measurements, performed on state-of-the-art gallium nitride (GaN) RF FETs for microwave and millimeter-wave applications.

Effects of SiON/III-nitride interface properties on device performances of GaN-based power field-effect transistors

In this work, we performed an investigation on the electrical characteristics of the interfaces of SiON/AlGaN and SiON/GaN by fabricating a partially gate-recessed metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) and a fully gate-recessed metal-insulator-semiconductor field-effect transistor (MIS-FET). The fabricated MIS-HEMT exhibits a smaller static on-resistance (R on) of 12.7 Ω · mm, while the MIS-FET achieves the normally-off operation. As a result of over-etching in the gate trench, a higher trap state density of 2 × 1013 cm−2eV−1 at the SiON/GaN interface in comparison to SiON/AlGaN interface (8 × 1012 cm−2eV−1), leading to a more obvious degradation of subthreshold swing, was extracted after performing the high temperature I DS−V GS tests. In addition, compared with the MIS-FET, the traps distributed at the SiON/AlGaN interface are found to be located at a deeper energy level, which make the device more stress sensitive and can cause a greater threshold voltage (V th) shift in the drain-bias stress measurement. The drain-bias stress at off-state increases the ionized trap density and makes the ionized traps unrecoverable within 1000 s in the MIS-HEMT. This work reveals the different properties of traps states at the SiON/AlGaN and SiON/GaN interfaces, and their effects on the device reliability.

Design of Ion-Implanted Junction Termination Extension for Vertical GaN Pin Rectifiers

In recent years, GaN bipolar switches have attracted much research interests for the implementation of high-power and high-voltage applications that laterally-scaled GaN-based power field-effect transistors were not optimally implemented. In the context of vertical power device design, a proper electric field engineering would be of crucial importance to exploit the device performance that could potentially reach the theoretical power switching limit for a given material system. In this report, we studied the effectiveness of the floating guard ring design of a vertical GaN p-i-n (PIN) rectifiers for kV-range applications using a planar device fabrication that involves the use of ion-implantation as a mean of device isolation and the formation of floating guard rings. We found the gap between floating guard ring has major impact on the electric field distribution in vertical PIN rectifiers. As a result, 1 kV of blocking voltage was achieved by 6 floating guard ring design using nitrogen-ion implanted isolation.

Current modulation in graphene p–n junctions with external fields

In this work we describe a proposal for a graphene-based nanostructure that modulates electric current even in the absence of a gap in the band structure. The device consists of a graphene p–n junction that acts as a Veselago lens that focuses ballistic electrons on the output lead. Applying external (electric and magnetic) fields changes the position of the output focus, reducing the transmission. Such device can be applied to low power field effect transistors, which can benefit from graphene’s high electronic mobility.

Gallium Nitride Integration: Breaking Down Technical Barriers Quickly [Expert View

An integrated circuit (IC) made using gallium nitride on silicon (GaN-on-Si) substrates has been in production for more than five years. The September 2018 issue of IEEE Power Electronics Magazine included an update on the GaN integration of power devices, which indicated rapid progress toward a complete system-on-a-chip solution. This article stepped through various phases of integration, from pure discrete devices to monolithic half bridge devices, to power field-effect transistors (FETs) that included their own monolithically integrated driver. Since the 2018 update, there has been a good deal of progress in the state of GaN integration, primarily spearheaded by two different GaN companies, Efficient Pow - er Conversion (EPC) and Navitas Semiconductor.

Stability and Reliability of Lateral GaN Power Field-Effect Transistors

GaN electronics constitutes a revolutionary technology with power handling capabilities that amply exceed those of Si and other semiconductors in many applications. RF, microwave, and millimeter-wave GaN-based power amplifiers are now deployed in commercial communications, radar, and sensing systems. GaN power transistors for electrical power management are also starting to reach the marketplace. From the dawn of this technology, inadequate transistor stability and reliability have represented stumbling blocks preventing widespread commercial use of GaN electronics. Intense research has been devoted to addressing these issues, and great progress has taken place recently. This article reviews some of the most interesting and significant stability and reliability issues that have plagued GaN power field-effect transistors for RF and power management applications.

Impoving energy characteristics of the welding power sources for TIG-AC welding

This paper proposes a circuit solution and a control algorithm for a welding power source for TIG-AC welding with improved energy characteristics. The source is made using a welding transformer and a low-voltage series active power filter on power field effect transistors with a low channel resistance. The transformer used can be with normal or increased leakage. The proposed source is characterized by improved technical parameters due to the possibility to form V-I characteristic with the required stiffness without switching the welding transformer taps. Control scheme ensures the elimination of a DC component of welding current during a TIG-AC process; it is also possible to control the waveshape of a welding current. Also, a "soft" arc ignition based on the Lift-Arc principle is provided, which positively affects the service life of a non-fusible electrode. The developed source is distinguished by a possibility to work in a reactive power compensation mode. This reduces the consumption of reactive power by electrical complexes with welding power sources and reduces a current loading on the distribution network. Application of the proposed principle to construct a source for arc welding with an alternating current makes it possible to modernize existing transformer sources by installing an active power filter unit in them. That would improve consumer properties of the sources by improving the stability of a welding arc, by smooth regulation of welding current, reducing the effects of a network voltage fluctuations on quality of the welding process. It eliminates the need to apply ballast resistors for adjusting a welding current, as well as the block of capacitors to eliminate the magnetization of a transformer during the TIG-AC process. The proposed source could be used not only to implement TIG-AC, but the MMA, MIG, MAG alternating current welding processes

Impact of non-ideal waveforms on GaN power FET in magnetic resonant wireless power transfer system

GaN field-effect transistors (FET) have low conduction and switching losses in high-frequency (>MHz) resonant wireless power transfer systems. Nevertheless, such systems impose a unique stress on GaN FETs owing to their non-ideal voltage waveforms. In this work, we report the observed non-ideal behavior in a 6.78 MHz magnetic resonant wireless transfer system that employs class-D GaN power amplifiers. The non-ideal waveform phenomenon existing at the output of the power amplifier is explained. The study analyzes the causes of this phenomenon, including the coupling coefficient k of the coil, the DC input voltage of the amplifier, and the load on the receiver. Each parameter is simulated and analyzed using LTspice. The influence of the phenomenon on the on-state resistance of the GaN device is proved in an experimental measurement, and the cause of the phenomenon is explained. The study combines a theoretical simulation and an experimental test to discuss the effect of this phenomenon on GaN power devices and proposes the corresponding solutions, which include the limitation of voltage, current, and power of the system, thermal management, and other protection measures.

Comparative performance evaluation of lateral and vertical GaN high-voltage power field-effect transistors

We have evaluated specific on-state resistance (Ron,sp) and switching performance of various GaN power field-effect transistors (FETs) with 600 and 1200 V ratings using analytical calculation and numerical simulation. The normally-off GaN power FET family includes lateral p-GaN gate high electron mobility transistors (HEMTs), lateral metal-oxide-semiconductor (MOS) channel HEMTs, current aperture vertical electron transistors (CAVETs) and vertical U-shaped trench-gate MOS field-effect transistors (UMOSFETs). This study shows the advantages of vertical GaN power FETs over lateral GaN power HEMTs. These advantages include lower Ron,sp and smaller switching energy loss, especially at higher blocking voltages (1200 V). At 600 V, lateral P-GaN gate HEMTs are competitive with vertical power FETs. Vertical GaN CAVETs perform better than both lateral HEMTs and vertical UMOSFETs at both voltage ratings, benefiting from its lowest Ron*QG figure-of-merit.

Design of Micro Energy Pulse Power Supply for Multi Electrode Synchronous Micro-EDM

In order to solve the problem of low efficiency of micro-EDM, a micro energy pulse power supply for multi electrode synchronous micro-EDM was designed. The power supply outputs high-frequency PWM signals from the processor STM32F103RCT6, which processed by the discharge control loop can drive the high power field effect transistor to control the capacitance charge-discharge. Capacitance quantitative energy storage and pulse width adjustment of micro energy pulse are realized by changing the duty cycle of PWM. It combines with gap state detection technology to distinguish the gap state of each electrode and adjust the gap between the workpiece and electrode in time. The Experimental tests show that the power supply can achieve efficient and stable EDM.

(Invited) High Power Diamond Devices with 2-D Transport Channels

Diamond transistors with surface 2D conduction channels are projected to be radiation hard with respect to neutrons. However, ionizing radiation hardness may be a problem due to the disruption of the 2D hole concentration. In this paper, the processing of three terminal devices with 2D surface conducting channels is presented as well as analysis of device transfer characteristics. This paper addresses the fabrication, radiation induced defects and device characteristics of microwave power field effect transistors (FET) built on 1) high quality diamond surfaces exploiting the 2 dimensional surface conductivity, and 2) the surface two dimensional “hydrogen terminated” conduction layer in diamond single crystals grown by CVD. Diamond is an ultra-wide bandgap semiconductor material that exhibits a number of ideal properties for future power and RF electronics applications beyond the current generation of SiC- and GaN-based technology. These properties include a bandgap of 5.5 eV, a high breakdown field (>10 MV/cm), high theoretical room-temperature carrier mobilities (>3800 cm2/V*sec), extremely high thermal conductivity (>22 W/cm*K), and excellent mechanical and thermal stability in vacuum. However, diamond doping is difficult, as the activation energies for typical dopants (B, P) exceed 0.37 eV and lead to very low dopant activation levels.[3] This drawback of dopant activation efficiency has been, in part, mitigated by two-dimensional conductivity found in hydrogen-terminated diamond surfaces. Hydrogen-termination (usually accomplished via exposure to hydrogen plasma) has been found to create a C-H surface dipole layer that reduces the carrier ionization energy by nearly 1.5 eV. Adsorbed species, such as atmospheric H2O, NO2, or intentionally-introduced passivation species contact this dipole layer, and together generate a two-dimensional hole gas (2DHG) with 1013-1014 holes/cm2 carrier density several nanometers below the diamond surface. Hydrogen-terminated diamond has been used as the basis for metal-semiconductor field effect transistors (MESFETs) and metal-oxide-semiconductor field effect transistors (MOSFETs) hydrogen-terminated diamond. Both unpassivated and passivated surface conduction devices have been fabricated. In the case of unpassivated devices, exposure to air (and thus atmospheric H2O) causes the devices to exhibit sheet charge densities in the 1013 holes/cm2 range.[1] MESFETs typically rely on Au metal for Ohmic contacts and Al metal for Schottky contacts to the hydrogen-terminated diamond. These devices have been normally-on devices, with threshold voltages around between -1V to +1V, depending on device dimensions.[1-4] MOSFETs fabricated using atomic layer deposited (ALD) oxides such as Al2O3 have been fabricated with either normally-off or normally-on behavior, depending on thermal history. Annealing of these devices at 180°C caused the devices to switch from normally-on to normally-off, with threshold voltages again in the range of ±1V range; the change was likely due to the removal of adsorbed species in the unpassivated diamond surfaces between the source, gate, and drain regions in the device, causing a reduction in the 2DHG sheet carrier density.[4] The diamond materials and surface preparation supplied by Euclid Techlabs using proprietary processes to produce defect free, ultra-smooth (Sa ~ 0.2 nm) diamond surfaces and buried boron ‘delta doped’ CVD layers. Euclid techlabs has demonstrated the delta doped transport channels in Diamond have mobilities in excess of 700 cm2/V sec. Device design and process science development was carried out within the facilities of the UMD NanoCenter and the NanoFab Lab. Radiation testing has been carried out at the radiation facilities of the University of Maryland. Device electrical performance and characterization has been carried out. We perform baseband noise, as well transconductance/output resistance dispersion characterization of 2D Surface Channel Diamond FETs fabricated under different processes and having different geometry and designs in order to identify device defects and their reliability and their susceptibility to radiation effects. The impact of the various types of noise on device defect and radiation hardness will be reported. Materials characterization techniques including Raman spectroscopy (strain, sp2 vs sp3 bonding), FTIR, and SIMS. Common diamond point defects are characterized by photoluminescence and FTIR.

(Invited) High Power Diamond Devices with 2-D Transport Channels

This paper addresses the fabrication, radiation induced defects and device characteristics of microwave power field effect transistors (FETs) built on 1) high quality diamond surfaces exploiting the 2 dimensional delta channel conductivity, and 2) the surface two dimensional “hydrogen terminated” conduction layer in diamond single crystals grown by CVD.

Lossless turn-off switching projection of lateral and vertical GaN power field-effect transistors

New physical insights into switching loss evaluation are applied to GaN power field-effect transistors, including p-AlGaN gate HEMTs, MOS channel HEMTs, and vertical UMOSFETs. Internal channel current is used to calculate true switching loss values for both turn-on and -off. In contrast to conventional terminal current-based loss calculations, energy stored in device output capacitances during turn-off and dissipated during turn-on is counted as turn-on loss rather than turn-off loss. At appropriate RG and off-state VG values, lossless turn-off can be achieved for MOS channel HEMTs and UMOSFETs, but not for p-AlGaN gate HEMTs. In appropriate circuit applications, near zero total switching loss can be realized by combining lossless turn-off and zero-voltage turn-on.