This article delves into the specifics of NPN and PNP transistors, their working principles, applications, comparisons, and factors to consider when choosing between them.

Understanding NPN vs PNP Transistors: A Comprehensive Guide

Topological materials move electrons along their surface and edges without any loss, making them promising materials for dissipationless, high-efficiency electronics. Researchers are especially interested in using these materials as transistors, the backbone of all modern electronics. But there’s a problem: Transistors switch electronic current on and off, but it’s difficult to turn off the dissipationless flow of electrons in topological materials. &nbsp;Now, Harvard University researchers have designed and simulated the first topological acoustic transistors — with sound waves instead of electrons — and proposed a connection architecture to form a universal logic gate that can switch the flow of sound on and off.&nbsp;“Since the advent of topological materials around 2007, there has been a lot of interest in developing a topological electronic transistor,” said&nbsp;<a href="https://www.seas.harvard.edu/person/jenny-hoffman" target="_blank">Jenny Hoffman</a>, the Clowes Professor of Science at the&nbsp;<a href="https://www.seas.harvard.edu/" target="_blank">Harvard John A. Paulson School of Engineering and Applied Sciences&nbsp;</a>(SEAS) and the Department of Physics. &nbsp;“Although the materials we used won't yield an electronic topological transistor, our general design process applies to both quantum materials and photonic crystals, raising hopes that electronic and optical equivalents may not be far behind.”&nbsp;The research is published in Physical Review Letters.&nbsp;By using acoustic topological insulators, the researchers were able to sidestep the complicated quantum mechanics of electron topological insulators.&nbsp;“The equations for sound waves are exactly solvable, which allowed us to numerically find just the right combination of materials to design a topological acoustic waveguide that turns on when heated, and off when cooled,” said Harris Pirie, a former graduate student in the Department of Physics and first author of the paper.&nbsp;Pirie is currently a Marie Curie Postdoctoral Fellow at Oxford University.The researchers used a honeycomb lattice of steel pillars anchored to a high-thermal-expansion plate, sealed in an air-tight box. The lattice has slightly larger pillars on one half, and slightly smaller pillars on the other half. These differences in size and spacing of the pillars determine the topology of the lattice, whether sound waves can travel along a designated channel or not. The researchers then designed a second device that converts ultrasound into heat.&nbsp;The heat expands the pillar lattice and changes the topology of the waveguide. When coupled together, these two devices allow the output of one waveguide to control the state of the next, just as the electrons flowing in a conventional transistor can toggle other transistors.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1641469960524-ezgif-7-8bded6a916.gif" style="width: 766px;" class="fr-fic fr-dib">These acoustic topological switches are scalable, meaning the same design used with ultrasonic frequencies at the centimeter scale could also work at sub-millimeter sizes and frequencies commonly used to transmit surface acoustic waves, which may help to overcome limitations in integrated phononic circuits.“The control of topologically protected acoustic transport has applications in a number of important fields including efficient acoustic-noise reduction, one-way acoustic propagation, ultrasound imaging, echolocation, acoustic cloaking, and acoustic communications,” said Pirie.These acoustic metamaterials could also be used as a teaching tool.&nbsp;“Unlike quantum-mechanical systems, acoustic metamaterials are straightforward, tangible, and intuitive. They serve as an accessible entry point to cutting edge topics in condensed matter physics, including topological insulators,” said Hoffman.The team plans to make a public-facing demonstration of these devices that students or museum visitors can touch, toggle, and hear.The research was co-authored by Harvard undergraduates Shuvom Sadhuka and Radu Andrei, as well as MIT graduate student Jennifer Wang.

Model of a honeycomb lattice that can be rapidly expanded using SMA coils to create a high thermal expansion coefficient. (Credit: Hoffman Lab/Harvard SEAS)

Sound waves may pave the way for topological electronic transistors

The first topological acoustic transistor

In this episode, we talk about the injectable microchip from Columbia University along with its applications in clinical settings, a global effort to develop two dimensional transistors, and a NASA Pathways Intern who created an AI powered system capable of detecting spacecraft failures. As always, you can find these and other interesting &amp; impactful engineering articles on Wevolver.com.<iframe height="200px" width="100%" frameborder="no" scrolling="no" seamless="" src="https://player.simplecast.com/ef862d63-d4d0-42c8-a100-d5826f66fcc2?dark=false" class="fr-draggable" data-lf-form-tracking-inspected-kn9eq4roawkarlvp="true" data-lf-yt-playback-inspected-kn9eq4roawkarlvp="true" data-lf-vimeo-playback-inspected-kn9eq4roawkarlvp="true"></iframe>&nbsp;<h3>EPISODE NOTES</h3>Take a few seconds to leave us a review. It really helps! <a href="https://apple.co/2RIsbZ2" target="_blank">https://apple.co/2RIsbZ2</a> if you do it and send us proof, we’ll give you a shoutout on the show.&nbsp;(0:42) - Injectable Microchips:Researchers at Columbia University have developed a microchip the size of a grain of salt that can be injected into a patient and act as a wireless temperature sensor. The chip is powered by and communicates to a standard ultrasound probe from outside the body.&nbsp;(9:00) - 2D Transistors:Moore’s law has dictated the progress of computational power for the past few decades but lately, it seems like we’ve hit the physical limit of transistor development. There’s now an international effort led by MIT and UC Berkeley to explore 2D transistors which could pave the way for keeping up with Moore’s Law again.&nbsp;(17:10) - AI For Spacecraft Diagnosis:NASA Pathways intern Evanna Gizzi has been working on Research in Artificial Intelligence for Spacecraft Resilience (RAISR) which aims to autonomously detect the root cause of spacecraft failures. RAISR is like an AI engineer that lives in the brain of a spacecraft to identify and remedy spacecraft failures.--About the podcast:Every day, some of the most innovative universities, companies, and individual technology developers share their knowledge on Wevolver. To ensure we can also provide this knowledge for the growing group of podcast listeners, we started a collaboration with two young engineers, Daniel Scott Mitchell &amp; Farbod Moghaddam who discuss the most interesting content in this podcast series.&nbsp;To learn more about this show, please visit the&nbsp;<a href="https://www.wevolver.com/profile/the.next.byte" target="_blank">shows page</a>. By following the page, you will get automatic updates by email when a new show is published.Be sure to give us a follow and review on <a href="https://podcasts.apple.com/nl/podcast/the-next-byte/id1548255861?l=en" rel="nofollow" target="_blank">Apple</a> podcasts, <a href="https://open.spotify.com/show/6lPPsRtegnivsRUEsQ09R7?si=IPMiah7xT_apJtPjqvXMlA" rel="nofollow" target="_blank">Spotify</a>, and most of your favorite podcast platforms!

In this episode, we talk about the injectable microchip from Columbia University along with its applications in clinical settings, a global effort to develop two dimensional transistors, and a NASA Pathways Intern who created an AI powered system capable of detecting spacecraft failures.

Podcast: Injectable Microchips, 2D Transistors, AI For Spacecraft Diagnosis

Since the discovery of graphene, two-dimensional materials have been the focus of materials research. Among other things, they could be used to build tiny, high-performance transistors. Researchers at ETH Zurich and EPF Lausanne have now simulated and evaluated one hundred possible materials for this purpose and discovered 13 promising candidates.&nbsp;With the increasing miniaturization of electronic components, researchers are struggling with undesirable side effects: In the case of nanometer-scale transistors made of conventional materials such as silicon, quantum effects occur that impair their functionality. One of these quantum effects, for example, is additional leakage currents, i.e. currents that flow "astray" and not via the conductor provided between the source and drain contacts.It is therefore believed that Moore's scaling law, which states that the number of integrated circuits per unit area doubles every 12-18 months, will reach its limits in the near future because of the increasing challenges associated with the miniaturisation of their active components. This ultimately means that the currently manufactured silicon-based transistors — called FinFETs and equipping almost every supercomputer — can no longer be made arbitrarily smaller due to quantum effects.<h2>Two-dimensional beacons of hope</h2>However, a new study by researchers at ETH Zurich and EPF Lausanne shows that this problem could be overcome with new two-dimensional (2-D) materials — or at least that is what the simulations they have carried out on the "Piz Daint" supercomputer suggest.The research group, led by Mathieu Luisier from the Institute for Integrated Systems (IIS) at ETH Zurich and Nicola Marzari from EPF Lausanne, used the research results that Marzari and his team had already achieved as the basis for their new simulations: Back in 2018, 14 years after the discovery of graphene first made it clear that two-dimensional materials could be produced, they used complex simulations on "Piz Daint" to sift through a pool of more than 100,000 materials; they extracted 1,825 promising components from which 2-D layers of material could be obtained.The researchers selected 100 candidates from these more than 1,800 materials, each of which consists of a monolayer of atoms and could be suitable for the construction of ultra-scaled field-effect transistors (FETs). They have now investigated their properties under the "ab initio" microscope. In other words, they used the CSCS supercomputer "Piz Daint" to first determine the atomic structure of these materials using density functional theory (DFT). They then combined these calculations with a so-called Quantum Transport solver to simulate the electron and hole current flows through the virtually generated transistors. The Quantum Transport Simulator used was developed by Luisier together with another ETH research team, and the underlying method was awarded the Gordon Bell Prize in 2019.<h2>Finding the optimal 2-D candidate</h2>The decisive factor for the transistor’s viability is whether the current can be optimally controlled by one or several gate contact(s). Thanks to the ultra-thin nature of 2-D materials — usually thinner than a nanometer — a single gate contact can modulate the flow of electrons and hole currents, thus completely switching a transistor on and off."Although all 2-D materials have this property, not all of them lend themselves to logic applications," Luisier emphasizes, "only those that have a large enough band gap between the valence band and conduction band.” Materials with a suitable band gap prevent so-called tunnel effects of the electrons and thus the leakage currents caused by them. It is precisely these materials that the researchers were looking for in their simulations.Their aim was to find 2-D materials that can supply a current greater than 3 milliamperes per micrometre, both as n-type transistors (electron transport) and as p-type transistors (hole transport), and whose channel length can be as small as 5 nanometres without impairing the switching behaviour. "Only when these conditions are met can transistors based on two-dimensional materials surpass conventional Si FinFETs," says Luisier.<h2>The ball is now in the experimental researchers' court</h2>Taking these aspects into account, the researchers identified 13 possible 2-D materials with which future transistors could be built and which could also enable the continuation of Moore's scaling law. Some of these materials are already known, for example black phosphorus or HfS2, but Luisier emphasizes that others are completely new — compounds such as Ag2N6 or O6Sb4."We have created one of the largest databases of transistor materials thanks to our simulations. With these results, we hope to motivate experimentalists working with 2-D materials to exfoliate new crystals and create next-generation logic switches," says the ETH professor. The research groups led by Luisier and Marzari work closely together at the National Centre of Competence in Research (NCCR) MARVEL and have now published their latest joint results in the journal ACS Nano. They are confident that transistors based on these new materials could replace those made of silicon or of the currently popular transition metal dichalcogenides.<hr>This text by Simone Ulmer first appeared in English on the <a href="https://www.cscs.ch/science/chemistry-materials/2020/simulation-microscope-examines-transistors-of-the-future/" target="_blank">CSCS</a> website.&nbsp; &nbsp; &nbsp; &nbsp;<h2>Reference</h2>Klinkert C, Szabo A, Stieger C, Campi D, Marzari N &amp; Luisier M: 2-D Materials for Ultra-Scaled Field-Effect Transistors: Hundred Candidates under the Ab Initio Microscope, ACS Nano (2020), DOI: <a href="https://dx.doi.org/10.1021/acsnano.0c02983" target="_blank">10.1021/acsnano.0c02983</a><hr>Source: Simone Ulmer, <a href="https://ethz.ch/en/news-and-events/eth-news/news/2020/08/simulation-microscope-examines-transistors.html" rel="noopener noreferrer" target="_blank">ETH Zurich</a>.

Structure of a single-​gate FET with a channel made of a 2-D material. Arranged around it are a selection of 2-D materials that have been investigated. (Graphics: ETH Zurich / EPFL / CSCS)

Since the discovery of graphene, two-​dimensional materials have been the focus of materials research. Among other things, they could be used to build tiny, high-​performance transistors.

transistors

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"Simulation microscope" examines transistors of the future