semiconductor

56 Articles

Homebrew Electron Beam Lithography With A Scanning Electron Microscope

December 19, 2024 by 7 Comments

If you want to build semiconductors at home, it seems like the best place to start might be to find a used scanning electron microscope on eBay. At least that’s how [Peter Bosch] kicked off his electron beam lithography project, and we have to say the results are pretty impressive.

Now, most of the DIY semiconductor efforts we’ve seen start with photolithography, where a pattern is optically projected onto a substrate coated with a photopolymer resist layer so that features can be etched into the surface using various chemical treatments. [Peter]’s method is similar, but with important differences. First, for a resist he chose poly-methyl methacrylate (PMMA), also known as acrylic, dissolved in anisole, an organic substance commonly used in the fragrance industry. The resist solution was spin-coated into a test substrate of aluminized Mylar before going into the chamber of the SEM.

As for the microscope itself, that required a few special modifications of its own. Rather than rastering the beam across his sample and using a pattern mask, [Peter] wanted to draw the pattern onto the resist-covered substrate directly. This required an external deflection modification to the SEM, which we’d love to hear more about. Also, the SEM didn’t support beam blanking, meaning the electron beam would be turned on even while moving across areas that weren’t to be exposed. To get around this, [Peter] slowed down the beam’s movements while exposing areas in the pattern, and sped it up while transitioning to the next feature. It’s a pretty clever hack, and after development and etching with a cocktail of acids, the results were pretty spectacular. Check it out in the video below.

It’s pretty clear that this is all preliminary work, and that there’s much more to come before [Peter] starts etching silicon. He says he’s currently working on a thermal evaporator to deposit thin films, which we’re keen to see. We’ve seen a few sputtering rigs for thin film deposition before, but there are chemical ways to do it, too.

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Particle Physics On A Small, Affordable PCB

July 13, 2024 by 7 Comments

Experimenting in the world of particle physics probably brings to mind large, expensive pieces of equipment like particle accelerators, or at least exotic elements or isotopes that most of us can’t easily find. But plenty of common objects emit various particles, and it turns out that detecting these particles does not require government backing or acres of test equipment. In fact, you can get this job done with a few readily-available parts and [Tim] shows us how it’s done with his latest project.

The goal of his build is to have a working particle detector for less than $10 per board, although he’s making them in bulk to be used in an educational setting. The board uses a set of photodiodes enclosed in a protective PCB sandwich to detect beta particles from a Potassium-40 source. The high-energy electron interacts with the semiconductor in the photodiode and creates a measurable voltage pulse, which can be detected and recorded by the microcontroller on the board. For this build an RP2040 chip is being used, with a number of layers of amplification between it and the photodetector array used to get signals that the microcontroller can read.

Getting particle physics equipment into the hands of citizen scientists is becoming a lot more common thanks to builds like this which leverage the quirks of semiconductors to do something slightly outside their normal use case, and of course the people building them releasing their projects’ documentation on GitHub. We’ve also seen an interesting muon detector with a price tag of around $100 and an alpha particle detector which uses a copper wire with a high voltage to do its work.

Almost Making A Camera Sensor From Scratch

May 4, 2024 by 5 Comments

On our travels round the hardware world we’ve encountered more than one group pursuing the goal of making their own silicon integrated circuits, and indeed we’ve seen [Sam Zeloof] producing some of the first practical home-made devices. But silicon is simply one of many different semiconductor materials, and it’s possible to make working semiconductor devices in a less complex lab using some of the others. As an example, [Breaking Taps] has been working with copper (II) oxide, producing photodiodes, and coming within touching distance of a working matrix array.

The video below the break is a comprehensive primer on simple semiconductor production and the challenges of producing copper (II) oxide rather than the lower temperature copper (I) oxide. The devices made have a Schottky junction between the semiconductor and an aluminium conductor, and after some concerns about whether the silicon substrate is part of the circuit and even some spectacular destruction of devices, he has a working photodiode with a satisfying change on the curve tracer when light is applied. The finale is an array of the devices to form a rudimentary camera sensor, but sadly due to alignment issues it’s not quite there  yet. We look forward to seeing it when he solves those problems.

As we’ve seen before, copper oxide isn’t the only semiconductor material outside the silicon envelope.

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Shuji Nakamura: The Man Who Gave Us The Blue LED Despite All Odds

February 14, 2024 by 68 Comments

With the invention of the first LED featuring a red color, it seemed only a matter of time before LEDs would appear with other colors. Indeed, soon green and other colors joined the LED revolution, but not blue. Although some dim prototypes existed, none of them were practical enough to be considered for commercialization. The subject of a recent [Veritasium] video, the core of the problem was that finding a material with the right bandgap and other desirable properties remained elusive. It was in this situation that at the tail end of the 1980s a young engineer at Nichia in Japan found himself pursuing a solution to this conundrum.

Although Nichia was struggling at the time due to the competition in the semiconductor market, its president was not afraid to take a gamble on a promise, which is why this young engineer – [Shuji Nakamura] – got permission to try his wits at the problem. This included a year long study trip to Florida to learn the ins and outs of a new technology called metalorganic chemical vapor deposition (MOCVD, also metalorganic vapor-phase epitaxy). Once back in Japan, he got access to a new MOCVD machine at Nichia, which he quickly got around to heavily modifying into the now well-known two-flow reactor version which improves the yield.

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The Geometry Of Transistors

December 13, 2023 by 10 Comments

Building things in a lab is easy, at least when compared to scaling up for mass production. That’s why there are so many articles about fusion being right around the corner, or battery technology that’ll allow aviation to switch away from fossil fuels, or any number of other miraculous solutions that never come into being. They simply don’t scale or can’t be manufactured in a cost effective way. But even when they are miraculous and can be produced on a massive scale, as is the case for things like transistors, there are some oddities that come up as a result of the process of making so many. This video goes into some of the intricacies of a bipolar junction transistor (BJT) and why it looks the way it does.

The BJT in this video is a fairly standard NPN type, with three layers of silicon acting as emitter, base, and collector. Typically when learning about electronics devices the drawings of them are simplified two-dimensional block diagrams, but under a microscope this transistor at first appears nothing like the models shown in the textbook. Instead it resembles more of a bird’s foot with a few small wires attached. The bird’s foot shape is a result of attempting to lower the undesirable resistances of the device and improve its performance, and some of its other quirks are due to the manufacturing process. That process starts with a much larger layer of doped silicon that will eventually become the collector, and then the other two, much smaller, layers of the transistor deposited on top of the collector. This also explains while it looks like there are only two layers upon first glance, and also shows that the horizontal diagram used to model the device is actually positioned vertically in the real world.

For most of the processes in our daily lives, the transistor has largely been abstracted away. We don’t have to think about them in a computer that much anymore, and unless work is being done on high-wattage power electronics devices, radios, or audio amplifiers it’s not likely that an average person will run into a transistor. But this video goes a long way to explaining the basics of one of the fundamental building blocks of the modern world for those willing to take a dive into the physics. Take a look at this video as well for an intuitive explanation of the close cousin of the BJT, the field-effect transistor.

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MOSFETs — The Hidden Gate

December 8, 2023 by 11 Comments

How many terminals does a MOSFET have? Trick question since most have three leads, even though there are really four connections to the underlying device. It isn’t a conspiracy, though and [Aaron Lanterman] talks about how MOSFETs really work and why thinking of them as three-terminal devices can lead you astray in a recent video that you can watch below.

Like many people, [Aaron] points out the parallel between a triode vacuum tube and a MOSFET. That’s not surprising, since a solid-state tube was exactly what they were looking for when they developed the FET. Since tubes and FETs are both voltage controllers, it is easy to think of the gate as the grid, the source as the cathode, and the drain as the plate. But, [Aaron] shows this isn’t really a very accurate picture.

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Fastest Semiconductor May Also Be Most Expensive

November 9, 2023 by 26 Comments

Scientists have found what they think may be the fastest known semiconductor. Sounds great, right? But it happens to made from one of the rarest elements: rhenium. That rare element combines with selenium and chlorine to form a “superatom.” Unlike conventional semiconductor material, the superatom causes phonons to bind together and resist scattering. This should allow materials that can process signals in femtoseconds,

Rhenium was the last stable element to be found in 1925. It is primarily used in combination with nickel in parts of jet engines, although it is also known as a catalyst for certain reactions. It is very rare and has a high melting point, exceeded only by tungsten and carbon. When it was discovered, scientists extracted a single gram of the material by processing 660 kg of molybdenite. Because of its rarity, it is expensive, costing anywhere from $2,800 to $10,600 per kilogram.

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