Ved Gund’s research while affiliated with Cornell University and other places

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Publications (30)

(a) Cross Sect. schematic for the GaN HEMT with regrown contacts, and the high-K AlScN layer in the barrier layer is 5 nm thick. (b) AFM image of the as-grown sample surface. (c) SEM image of a processed HEMT, and (d) inset shows the zoomed-in image of a T-gate.
(a) Family I − V curves and (b) transfer characteristics of the device with Lg = 90 nm and Lsd = 600 nm. (c) Output current benchmark of AlScN HEMTs with previous reports.25–28).
(a) Current gain and unilateral gain of the device with Lg = 90 nm, showing fT/ fMAX = 92.4/134.3 GHz. A gain decay of −20 dB/dec is plotted with the dash lines to show fT and fMAX extrapolation. Vds and Vgs bias dependence of (b) fT and (c) fMAX extracted from U. The colors indicate frequencies on the contour maps.
Breakdown voltage scaling as a function of gate-drain separation ranging from 0.25 to 3.85 μm. The gate length of all measured devices is 90 nm.
AlScN/GaN HEMTs with 4 A/mm on-current and maximum oscillation frequency >130 GHz
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January 2025

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57 Reads

Kazuki Nomoto

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Joseph Casamento

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Aluminum Scandium Nitride (AlScN) is an attractive material for use as a lattice-matched epitaxial barrier layer in GaN high-electron mobility transistors (HEMTs). Here we report the device fabrication, direct current (DC) and radio frequency (RF) characteristics of epitaxial AlScN/AlN/GaN HEMTs on SiC substrates with regrown ohmic contacts. These devices show record high on-current of over 4 A/mm, high cutoff frequency (fT) of 92.4 GHz and maximum oscillation frequency ( fMAX ) of 134.3 GHz.

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Figure 1: Schematic of the pyroelectric high voltage generation system. a. Each pyroelectric crystal (5x5x5 mm 3 LiNbO3, coated with gold on the top and bottom surfaces) is surrounded with a 3D printed metal holder. b. The fluidic channel is used to heat and cool an array of crystals with running liquid. Charges generated on the crystals enable the local powering of actuators, or voltage delivery to a single storage capacitor.
Figure 2. Characterization of the thermal properties. a. An equivalent thermal circuit model consists of the metal channel, the thermal glue, and the pyroelectric crystal. The heated liquid is considered as an energy source with pulse output. b. The rate of temperature change happened on a LN crystal temperature is linearly proportional to the temperature of the running liquid.
Figure 3. Electrical characterization of the pyroelectric system. a. The electrical circuit of the system where a storage capacitor is connected to Lithium Niobate. A cantilever beam is used to measure voltage delivered to the capacitor. b. The maximum voltage delivered to three capacitors of 2, 10, and 47 pF. The solid lines represent exponential fitting of the data c. The maximum energy delivered to three capacitors.
Comparison of existing µ-HV supplies
Kilovolt Pyroelectric Voltage Generation and Electrostatic Actuation With Fluidic Heating

November 2024

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26 Reads

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Ved Gund

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Integrated micro power generators are crucial components for micro robotic platforms to demonstrate untethered operation and to achieve autonomy. Current micro robotic electrostatic actuators typically require hundreds to thousands of voltages to output sufficient work. Pyroelectricity is one such source of high voltages that can be scaled to small form factors. This paper demonstrates a distributed pyroelectric high voltage generation mechanism to power kV actuators using alternating exposure of crystals to hot and cold water (300C to 900C water temperature). Using this fluidic temperature control, a pyroelectrically generated voltage of 2470 V was delivered to a 2 pF storage capacitor yielding a 6.10 {\mu}J stored energy. A maximum energy of 17.46 {\mu}J was delivered to a 47 pF capacitor at 861 V. The recirculating water can be used to heat a distributed array of converters to generate electricity in distant robotic actuator sections. The development of this distributed system would enable untethered micro-robot to be operated with a flexible body and free of battery recharging, which advances its applications in the real world.

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(a) Schematic of AlBN/ β-Nb2N/Al2O3 heterostructure showing epitaxial registry, (b) XRD-RSM map showing AlBN 103, β-Nb2N 103, and Al2O3 119 Bragg reflections for sample with 18% B, (c) RHEED pattern of AlBN film with 18% B along11–20 zone axis, (d) AFM micrograph of AlBN film with 18% B, and (e) cross section of device used for electrical characterization.
(a)–(c) Triangular PUND waveform voltage pulses, output currents, and (d)–(f) P–E loops for AlBN with 0%, 4.7%, and 18% B samples, respectively.
(a) and (b) P–E loops and Ec, Pr values showing repeatability over multiple devices, (c) and (d) P–E loops and Ec values at various measurement frequencies on Al0.82B0.18N sample, (e) current density, electric field plot for AlBN samples with 0%, 4.7%, 18% B, and (f) a representative trapezoidal PUUNDD waveform voltage pulse, output current on Al0.82B0.18N sample.
(a) Typical PFM amplitude and phase loops measured on AlBN/ β-Nb2N/Al2O3 sample with ∼ 18% B measured at 300 kHz and at room temperature. Butterfly-shaped amplitude loops and hysteretic phase loops with ∼ 180° phase shift are observed. (b) PFM phase contrast image pattern after writing at +/−40 V indicating electrically written domains of opposite polarizations. The inner 10  × 10  μ m² domain region written with +40 V bias on the tip has downward polarization, and the outer region written with −40 V bias has an upward polarization. (c) AFM line scan profile along the marked line in inset optical micrograph taken after KOH etching (45% KOH, 25s) of the AlBN sample with different PFM poled regions written at +/−40 V. The unpoled region without PFM writing and the innermost rectangle region written with +40 V bias have nitrogen polarity, as it etches more rapidly than the region written with −40 V bias having metal polarity.
Fig. S3. (a), (b), (c), (d) PFM phase contrast image patterns of MBE AlBN sample with ∼4% B after writing the inner 10 µm × 10 µm area with +30 V, -30V PFM tip biases indicating repeatable switching of electrically written domains between states of opposite polarity. The as-grown nitrogen polar AlBN film without PFM poling is in-phase with the inner region after poling with +30 V PFM tip bias, whereas it is out-of-phase with the inner region after poling with -30 V PFM tip bias. (e), (f), (g) PFM phase contrast image patterns taken at 0, 5, and 10 minutes after poling. The pattern is clearly visible even after 10 minutes of poling, showing good retention.

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Ferroelectric AlBN films by molecular beam epitaxy

August 2024

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57 Reads

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3 Citations

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Ved Gund

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Kazuki Nomoto

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Debdeep Jena

We report the properties of molecular beam epitaxy deposited AlBN thin films on a recently developed epitaxial nitride metal electrode, Nb2N. While a control AlN thin film exhibits standard capacitive behavior, distinct ferroelectric switching is observed in the AlBN films with increasing Boron mole fraction. The measured remnant polarization Pr∼15 μC/cm² and coercive field Ec∼ 1.45 MV/cm in these films are smaller than those recently reported on films deposited by sputtering, due to incomplete wake-up, limited by current leakage. Because AlBN preserves the ultrawide energy bandgap of AlN compared to other nitride hi-K dielectrics and ferroelectrics, and it can be epitaxially integrated with GaN and AlN semiconductors, its development will enable several opportunities for unique electronic, photonic, and memory devices.

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FIG. 2. (a), (b), (c) triangular PUND waveform voltage pulses, output currents, and (d), (e), (f) P-E loops for AlBN with 0%, 4.7% and 18% B samples, respectively.
FIG. 3. (a), (b) P-E loops and E c , P r values showing repeatability over multiple devices, (c), (d) P-E loops and E c values at various measurement frequencies on Al 0.82 B 0.18 N sample, (e) Current density, electric field plot for AlBN samples with 0%, 4.7%, 18% B, and (f) a representative trapezoidal PUUNDD waveform voltage pulse, output current on Al 0.82 B 0.18 N sample.
FIG. 4. (a) Typical PFM amplitude and phase loops measured on AlBN/β -Nb 2 N/Al 2 O 3 sample with ∼ 18% B measured at 300kHz and at room temperature. Butterfly-shaped amplitude loops and hysteretic phase loops with ∼180 degree phase shift are observed. (b) PFM phase contrast image pattern after writing at +/-40 V indicating electrically written domains of opposite polarizations. The inner 10 × 10 µm domain region written with +40 V bias on the tip has downward polarization, and the outer region written with -40 V bias has an upward polarization. (c) AFM line scan profile along the marked line in inset optical micrograph taken after KOH etching (45% KOH, 25s) of AlBN sample with different PFM poled regions written at +/-40 V. The unpoled region without PFM writing and the innermost rectangle region written with +40 V bias have nitrogen polarity, as it etches more rapidly than the region written with -40V bias having metal polarity.
Fig. S3. (a), (b), (c), (d) PFM phase contrast image patterns of MBE AlBN sample with ∼4% B after writing the inner 10 µm × 10 µm area with +30 V, -30V PFM tip biases indicating repeatable switching of electrically written domains between states of opposite polarity. The as-grown nitrogen polar AlBN film without PFM poling is in-phase with the inner region after poling with +30 V PFM tip bias, whereas it is out-of-phase with the inner region after poling with -30 V PFM tip bias. (e), (f), (g) PFM phase contrast image patterns taken at 0, 5, and 10 minutes after poling. The pattern is clearly visible even after 10 minutes of poling, showing good retention.
Fig. S4. (a), (b), (c) PFM height, amplitude, and phase contrast image patterns of MBE AlBN film sample with 18% B taken after PFM writing at +/-40 V indicating electrically written domains of opposite polarization. The inner 10 µm × 10 µm region written with +40 V tip bias has downward polarization, and the outer region written with -40 V tip bias has upward polarization. (c), (d), (f) PFM height, amplitude, and phase contrast images collected at (10 µm, 0 µm) offset from the center of the PFM written region. The AlBN film region without PFM poling is in phase with the region written with +40 V bias to the PFM tip, whereas it is out of phase with the region written with -40 V bias to the PFM tip.

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Ferroelectric AlBN Films by Molecular Beam Epitaxy

July 2024

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170 Reads

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Ved Gund

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Kazuki Nomoto

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Debdeep Jena

We report the properties of molecular beam epitaxy deposited AlBN thin films on a recently developed epitaxial nitride metal electrode Nb2N. While a control AlN thin film exhibits standard capacitive behavior, distinct ferroelectric switching is observed in the AlBN films with increasing Boron mole fraction. The measured remnant polarization Pr of 15 uC/cm2 and coercive field Ec of 1.45 MV/cm in these films are smaller than those recently reported on films deposited by sputtering, due to incomplete wake-up, limited by current leakage. Because AlBN preserves the ultrawide energy bandgap of AlN compared to other nitride hi-K dielectrics and ferroelectrics, and it can be epitaxially integrated with GaN and AlN semiconductors, its development will enable several opportunities for unique electronic, photonic, and memory devices.

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FerroHEMTs: High-Current and High-Speed All-Epitaxial AlScN/GaN Ferroelectric Transistors

February 2023

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116 Reads

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K. Nomoto

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D. Jena

We report the first observation of ferroelectric gating in AlScN barrier wide-bandgap nitride transistors. These FerroHEMT devices realized by direct epitaxial growth represent a new class of ferroelectric transistors in which the semiconductor is itself polar, and the crystalline ferroelectric barrier is lattice-matched to the substrate. The FerroHEMTs reported here use the thinnest nitride high K and ferroelectric barriers to date to deliver the highest on currents at 4 A/mm, and highest speed AlScN transistors with fmax larger than 150 GHz observed in any ferroelectric transistor. The FerroHEMTs exhibit hysteretic Id Vgs loops with subthreshold slopes below the Boltzmann limit. A control AlN barrier HEMT exhibits neither hysteretic, nor sub Boltzmann behavior. While these results introduce the first epitaxial high K and ferroelectric barrier technology to RF and mm wave electronics, they are also of interest as a new material platform for combining memory and logic functionalities in digital electronics.

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Citations (17)

... The ability to control the chemical composition is critical for tuning properties such as remnant polarization, leakage current, and piezoelectric response. However, chemical methods often yield polycrystalline films, which may exhibit inferior electrical properties compared to epitaxial thin films due to grain boundaries that can trap charge carriers [5] Physical methods like pulsed laser deposition (PLD) [22,23], Molecular Beam Epitaxy (MBE) [24,25], and Sputtering [26] are preferred for producing high-quality epitaxial thin films. These techniques allow for precise control over film thickness and layering at the atomic level, enabling the creation of heterostructures and superlattices with tailored properties [15]. ...

Reference:

Advancements in Free-Standing Ferroelectric Films: Paving the Way for Transparent Flexible Electronics
Ferroelectric AlBN films by molecular beam epitaxy

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Ved Gund

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Kazuki Nomoto

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Debdeep Jena

... In 2009, it was discovered that substituting group-III transition metal Sc atoms into Al sites of AlN dramatically boosted its piezoelectricity, leading to the rapid adoption of AlScN for BAW filters for cellphones. 2 In 2019, it was discovered that AlScN is ferroelectric, 10 and in 2022 FerroHEMTs were realized by integrating AlScN epitaxially with GaN [12][13][14] . The thermodynamic stable crystal structure of ScN of energy bandgap ∼1.2 eV is cubic rocksalt, and of AlN of energy bandgap ∼6.1 eV is hexagonal wurtzite. ...

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Ferroelectric AlBN films by molecular beam epitaxy
AlScN High Electron Mobility Transistors: Integrating High Piezoelectric, High K Dielectric, and Ferroelectric Functionality
  • Citing Conference Paper

  • October 2023

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Kazuki Nomoto

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Debdeep Jena

... Hui et al. (2023) designed a neural net to predict quality and resistance of inkjet-printed silver lines in relation to various printing process parameters. Ivy et al. (2023) developed a ML-model to optically predict resistance of inkjet-printed resistors based on their geometry and texture features, using a high-resolution color scanner. Gafurov et al. (2022) utilized deep-learning algorithms for the optical quality assessment and parameter identification of screen-printed lines. ...

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Image-based identification of optical quality and functional properties in inkjet-printed electronics using machine learning
Feature-Based Machine Learning for Predicting Resistances in Printed Electronics
  • Citing Conference Paper

  • July 2023

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Yutong Xie

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Theo Lobo

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... Such new FE devices, manufacturable through microfabrication processes also leveraged to build MEMS/NEMS components, have paved the way towards memory devices with lower programming voltages than the EEPROM counterparts [28]- [31]. Among the recently discovered FE devices, the ones based on Hafnium Zirconium Oxide (Hf 0.5 Zr 0.5 O 2 or "HZO") have garnered considerable attention in the past few years [32]- [39]. HZO can be manufactured through standard semiconductor processes, presents a good compatibility with silicon-based substrates, has a wide bandgap, exhibits high dielectric constant and suffers from low dielectric losses. ...

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A Radiofrequency Threshold Sensing System Using a Hf0.5Zr0.5O2 Device and a Microacoustic Piezoelectric Resonant Sensor
Programmable Ferroelectric HZO NEMS Mechanical Multiplier for in-Memory Computing
  • Citing Conference Paper

  • January 2023

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Ved Gund

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... This decrease in current density for scaled devices and ultra-thin barrier layers after several measurement cycles is not unexpected since the devices were not passivated. Figure 2(c) benchmarks the AlScN barrier GaN HEMTs of this work with earlier reports [25][26][27][28] of Al x Sc 1−x N/Al(Ga)N/GaN HEMTs. All AlScN barrier GaN HEMTs show high output currents compared to conventional GaN HEMTs with AlGaN or InAl (Ga)N barriers with similar device designs. ...

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AlScN/GaN HEMTs with 4 A/mm on-current and maximum oscillation frequency >130 GHz
FerroHEMTs: High-Current and High-Speed All-Epitaxial AlScN/GaN Ferroelectric Transistors
  • Citing Conference Paper

  • December 2022

J. Casamento

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K. Nomoto

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D. Jena

... In addition, HZO exhibits lower coercive fields and a higher remnant polarization than conventional perovskite-based ferroelectric films, making it a potential candidate for CMOS-compatible non-volatile memory devices [28]- [30]. However, until now, HZO FE devices have been polarized using DC-voltages or near-DC voltage pulses [35], [36]. Unfortunately, this polarization strategy is incompatible with the use of HZO to build memory devices in passive WSNs. ...

Reference:

A Radiofrequency Threshold Sensing System Using a Hf0.5Zr0.5O2 Device and a Microacoustic Piezoelectric Resonant Sensor
HZO-based FerroNEMS MAC for in-memory computing
  • Citing Article

  • November 2022

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Ved Gund

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... One way to address this limited tuneability is by integrating off-chip tuneable passives or RF switches but at the cost of degraded performance, excessive footprint and power consumption and integration challenges [20][21][22] . Another way is to use a ferroelectric material, such as aluminium scandium nitride [23][24][25][26][27][28] . However, aluminium scandium nitride has a very large coercive field and requires films several hundreds of nanometres thick to create ultraand super-high-frequency BAW resonators, resulting in large switching voltages (often exceeding 100 V) that are not readily available on chips. ...

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A ferroelectric-gate fin microwave acoustic spectral processor
Intrinsically Switchable GHz Ferroelectric ScAlN SAW Resonators
  • Citing Conference Paper

  • June 2022

Ved Gund

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Kazuki Nomoto

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... In addition, HZO exhibits lower coercive fields and a higher remnant polarization than conventional perovskite-based ferroelectric films, making it a potential candidate for CMOS-compatible non-volatile memory devices [28]- [30]. However, until now, HZO FE devices have been polarized using DC-voltages or near-DC voltage pulses [35], [36]. Unfortunately, this polarization strategy is incompatible with the use of HZO to build memory devices in passive WSNs. ...

Reference:

A Radiofrequency Threshold Sensing System Using a Hf0.5Zr0.5O2 Device and a Microacoustic Piezoelectric Resonant Sensor
Multi-level Analog Programmable Graphene Resistive Memory with Fractional Channel Ferroelectric Switching in Hafnium Zirconium Oxide
  • Citing Conference Paper

  • April 2022

Ved Gund

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... Using the BotFactory SV2 thermal Inkjet PCB printer, another machine can simultaneously print conductive and DIs. In [141], laser-induced graphene sensors and their wiring and packaging were fabricated following the printing process shown in Fig. 9. To begin fabrication, each device's four sets of three alignment windows are printed onto a 125-µm-thick Kapton board. ...

Reference:

A Review of Multimaterial Additively Manufactured Electronics and 4-D Printing/Origami Shape-Memory Devices: Design, Fabrication, and Implementation
Laser-Induced Graphene Pressure Sensors Manufactured via Inkjet PCB Printer Locally Producing Super-Sensitive and Cost-Effective Circular Diaphragm Pressure Gauges
  • Citing Conference Paper

  • July 2022

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Ved Gund

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