About

Akintunde Akinwande is the Thomas and Gerd Perkins Professor of Electrical Engineering and Computer Science at MIT. His research areas include Electronic, Magnetic, Optical and Quantum Materials and Devices, as well as Nanoscale Materials, Devices, and Systems. He is involved in developing systems that sense, process, and transmit energy and information, leveraging computational, theoretical, and experimental tools to create groundbreaking sensors, energy transducers, and physical substrates for computation. His work addresses shared challenges facing humanity through innovative system design and material development.

Research topics

• Materials science
• Optoelectronics
• Nanotechnology
• Chemistry
• Photochemistry
• Inorganic chemistry
• Organic chemistry
• Combinatorial chemistry
• Physics
• Electrical engineering
• Physical chemistry

Selected publications

• Radio Frequency Amplification in a Linear Crossed-Field Amplifier Using Cold Cathodes

  IEEE Transactions on Electron Devices · 2025-07-28

  article

  A low-frequency (561 MHz), injected beam, and linear format crossed-field amplifier (CFA) using gated field emission arrays (GFEAs) has been experimentally studied and compared with simulation. The CFA uses a copper wire on Teflon meander line circuit with retardation of ~21. Eight silicon tip GFEA dies were used as the injected electron source to provide up to 160 mA. A segmented end-collector system (nine electrodes) was used to measure the spatial variation of the beam current with and without gain. A gain of ~5.5 dB was measured for a sole-circuit voltage of −2.9 kV, an injected beam current of ~160 mA, an applied magnetic field of 0.0125 T, a radio frequency (RF) input power of 15 W, and a sole-circuit gap of 2 cm. A CST particle in-cell model shows a high gain (~1–2 dB) than the experiment, but the gain variation versus injected current, voltage, and magnetic field matches well. Variation with RF input power shows a significant decrease in gain above 15 W in the experiment with the decrease seen in simulation observed after 25 W. Analysis of the end-collector current shows a rapid decrease after 12 W in the experiment and 25 W in the simulation. This result occurs because the highly cycloidal electrons are close to the CFA circuit and get collected on the circuit before providing amplification energy. This observation is confirmed in simulation, which shows that the current going to the circuit rapidly increases and the end-collector current rapidly decreases. This effect also accounts for the higher gain observed in simulation. These experiments provide a basis for using gated field emitters to study beam–wave interactions in microwave vacuum electron devices.

  PublisherDOI

• Demonstration of Amplification in a Linear Format Crossed-Field Amplifier Using a Gated Field Emitter Injected Beam

  2025-06-15

  article

  High power crossed-field devices such as crossed-field amplifiers (CFA) are advantageous in terms of power density and efficiency. Disadvantages are low gain and relatively high noise. Improving gain and noise characteristics would make the CFA more appealing for a variety of applications. In this work, we demonstrated operation of a linear format CFA using a meander line slow wave circuit. Operating frequency is 561 MHz. The circuit is 138 mm long and 72.5 mm wide with endhats and a segmented (9 element) end collector. Circuit retardation is 21. The circuit to sole gap is 20 mm. An injected beam configuration using silicon gate field emitter arrays was used.

  PublisherDOI

• Impact of Anode Configuration on Performance of Field Emitter Arrays

  IEEE Transactions on Electron Devices · 2025-04-22 · 1 citations

  articleSenior author

  We demonstrate the first steps in engineering the anode of field emitter arrays (FEAs) for optimal vacuum packaging by studying a parallel anode–cathode configuration. As part of our study, we report an unexpected gate-controlled negative differential resistance (NDR) region in the output characteristics of FEA-based triodes. The FEA triode consists of an FEA cathode and a silicon MEMS anode that are separated by insulated standoffs to form a vacuum channel. The FEA cathode is an array of high-aspect nanowires connected in series with gated emitter tips. Electrons extracted by the gate–emitter voltage undergo ballistic transport to the anode. It is generally assumed that a parallel anode–cathode triode structure would be ideal due to its geometrical compactness and symmetry. In this work, an on-chip integrated flat silicon anode was fabricated to characterize the parallel configuration for well-defined anode-to-emitter distances of ≤100 μm. The observation of NDR in the “triode” operation regime, which is space-charge limited, suggests that the parallel anode–cathode structure will not be ideal for the integration of triodes for some circuit applications because of unfavorable electrostatics in the vacuum channel between the cathode and the anode. In addition, we demonstrated that the performance of the triodes could be engineered to reduce the ON-resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\textit{R}_{\biosc{on}}$</tex-math></inline-formula>) and increase the output current by varying the geometry and position of the anode.

  PublisherDOI

• Degradation of GaN field emitter arrays induced by O2 exposure

  Journal of Vacuum Science & Technology B Nanotechnology and Microelectronics Materials Processing Measurement and Phenomena · 2024-01-01 · 4 citations

  articleOpen access

  Field emitter arrays (FEAs) have the potential to operate at high frequencies and in harsh environments. However, they have been shown to degrade under oxidizing environments. Studying the effect of O2 on FEAs can help to understand the degradation mechanisms, identify the requirements for vacuum packaging, and estimate the lifetime of the device. In this work, the effect of O2 exposure on 100 × 100 gallium-nitride-field emitter arrays (GaN-FEAs) was studied. The GaN-FEAs were operated at 6 × 10−10 Torr with a 1000 V DC anode voltage and a 50 V DC gate voltage, where the anode current was 1 μA and the gate current was ≤4 nA. The devices were exposed to 10−7, 10−6, and 10−5 Torr of O2 for 100 000 L. The anode current dropped by 50% after 300 L and 98% after 100 000 L. It was observed that the degradation depends on the exposure dose, rather than pressure. The devices mostly degrade when they are ON, confirmed by exposing the device to O2 when the gate voltage was off, and also by the relation between the degradation and duty cycle when pulsing the gate. The results of O2 exposure were compared to Ar exposure to determine whether sputtering and changes in the surface geometry were the primary cause of degradation. The results suggest that changes in the work function and surface chemistry are the cause of emission degradation of GaN-FEA induced by O2.

  PublisherOA PDFDOI

• Particle-in-Cell Simulation and Experimental Setup of a Crossed-Field Amplifier

  2024-04-23

  article

  A 925 MHz, slow wave meander line crossed-field amplifier (CF A) structure was designed and developed using CST Microwave Studio. The structure has a phase velocity retardation of 24. The high frequency solver shows that the structure has a S11 of −40 dB at 925 MHz. For the PIC simulation, an already developed crossed field structure was used which includes a sole, a segmented collector, two end hats, and an injected electron source. PIC simulation shows that for a sole voltage of −3k V, a magnetic field of 150 G, an injected current of 150 mA, and an RF input power of 15 W, the gain of the structure was 10 dB. Also, experimental studies with a previously developed CF A structure are ongoing. This CF A structure was designed to operate at 600 MHz. An injected beam current of up to 60 mA using gated field emission arrays in an 8 die configuration has been tested. However, no gain was observed so far. Further experiments will be carried out using a higher injected beam current.

  PublisherDOI

• Field Emitter Failure Mechanisms and Harsh Environment Robustness Studies

  2024-04-23

  article

  Modern day field emitters can fail due to several mechanisms that are not well understood. This paper presents experiments that aim to identify the mechanisms behind failure. Two types of devices, Silicon gated field emitter arrays (SiGFEAs) and Titanium Silicon Oxy Nitride (TiSiON) lateral field emitter devices were characterized experimentally. Si-GFEAs were tested for arc occurrence time for a fixed gate voltage of 50 V and a fixed collector voltage of 200 V. The emitter was grounded. Initial results from the temporal response experiment show that the emitter experiences arcing first. However, future experiments will provide an accurate identification of the arc initiating electrode. For the planar device, a diode was chosen and IV characterization was performed at 50 °C and 400 °C. Experiments showed that for an applied collector voltage of 10 V, the field emission current was ≈ 5.5 nA before the heat treatment and was ≈ 2.75 nA after the 400 °C heat treatment. This reduction in current could be attributed to the removal of water vapor by heat treatment resulting in the reduction in the surface leakage current.

  PublisherDOI

• Operation of Si field emitter arrays in an N2 environment

  Vacuum · 2024-11-27

  articleOpen access

  Field Emitter Arrays (FEAs) have the potential to operate at high power, high frequencies, and endure harsh environments. However, vacuum packaging these devices poses a challenge due to the sensitivity of the emission phenomena to the surface properties of the cathode, such as the work function and the tip radius. Studying the effect of different residual gases on FEAs can enhance our understanding of the interaction between the emission surface and the environment and help estimate the permissible amount of residual gases within the package. In this study, the effect of N 2 exposure on 500 × 500 Silicon Field Emitter Arrays (Si-FEAs) was investigated. The device was exposed to 10 000 Langmuir (L) of N 2 at 10 −7 Torr. During the exposure, the anode current increased from 4.7 μA to 16 μA. However, this enhancement in current was temporary, and upon closing the leak valve, the anode current gradually returned to the pre-exposure level. No significant change in current was observed when the device was powered off during N 2 exposure. The extent of current enhancement showed a direct relationship with the partial pressure of N 2 . These results suggest that the presence of N 2 in a vacuum package does not degrade the performance of Si-FEAs. • Si-FEA emission current increased significantly in an N 2 environment. • The changes on the Si-FEA emission current happens only when the device is on and the changes are reversible. • O 2 partial pressure, compared to N 2 and Ar, limits Si-FEA lifetime.

  PublisherDOI

• Operation of Si Field Emitter Arrays in an N2 Environment

  SSRN Electronic Journal · 2024-01-01

  preprintOpen access
  PublisherDOI

• Silicon Field Emitter Arrays for Vacuum Integrated Circuits

  2024-07-15

  articleSenior author

  We present a proof-of-concept inverter based on silicon field emitter arrays (Si FEAs) that could be fabricated as a vacuum integrated circuit (IC). A circuit model for Si FEAs is developed, and the voltage transfer characteristics of the FEA inverter are simulated. In addition, a sample of 30 Si FEAs is characterized to determine the variations in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$a_{\text{FN}}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$b_{\text{FN}}$</tex> caused by the fabrication process. A Monte Carlo analysis is used to test the impact of variations on the FEA inverter performance.

  PublisherDOI

• Emission enhancement of GaN field emitter arrays in an N2 environment

  Journal of Vacuum Science & Technology B Nanotechnology and Microelectronics Materials Processing Measurement and Phenomena · 2024-07-01 · 3 citations

  article

  Field emitter arrays (FEAs) have the potential to operate at high frequencies and in harsh environments. However, the vacuum packaging of these devices poses a challenge due to the sensitivity of the emission phenomena to the surface properties of the cathode. Studying the effect of different residual gases on FEAs can help to understand the interaction of the emission surface with the environment and identify the feasibility and requirements for vacuum packaging. In this work, the effect of N2 exposure on 150 × 150 gallium-nitride-field emitter arrays (GaN-FEAs) was studied. The GaN-FEA was first operated at 10−9 Torr with a 1000 V DC anode voltage and a 50 V DC gate voltage, where the anode current was 6 μA. The device was then exposed to 10 000 l N2 at 10−7 Torr, and the anode current increased by 2.7 times during N2 exposure. The increase in the current was not permanent, and the current gradually decreased to its pre-exposure level after the N2 source was cut off. The results of N2 exposure were compared to Ar and O2.

  PublisherDOI

Frequent coauthors

• Luis Fernando Velásquez–García

  Massachusetts Institute of Technology

  45 shared

• Girish Rughoobur

  43 shared

• Nedeljko Karaulac

  Massachusetts Institute of Technology

  30 shared

• Jim Browning

  Boise State University

  26 shared

• Ranajoy Bhattacharya

  Boise State University

  25 shared

• Winston Chern

  Massachusetts Institute of Technology

  23 shared

• Ioannis Kymissis

  17 shared

• Blaise Gassend

  16 shared