semiconductor

59 Articles

Pulsed Deposition Points A Different Path To DIY Semiconductors

February 19, 2025 by 1 Comment

While not impossible, replicating the machines and processes of a modern semiconductor fab is a pretty steep climb for the home gamer. Sure, we’ve seen it done, but nanoscale photolithography is a demanding process that discourages the DIYer at every turn. So if you want to make semiconductors at home, it might be best to change the rules a little and give something like this pulsed laser deposition prototyping apparatus a try.

Rather than building up a semiconductor by depositing layers of material onto a silicon substrate and selectively etching features into them with photolithography, [Sebastián Elgueta]’s chips will be made by adding materials in their final shape, with no etching required. The heart of the process is a multi-material pulsed laser deposition chamber, which uses an Nd:YAG laser to ablate one of six materials held on a rotating turret, creating a plasma that can be deposited onto a silicon substrate. Layers can either be a single material or, with the turret rapidly switched between different targets, a mix of multiple materials. The chamber is also equipped with valves for admitting different gases, such as oxygen when insulating layers of metal oxides need to be deposited. To create features, a pattern etched into a continuous web of aluminum foil by a second laser is used as a mask. When a new mask is needed, a fresh area of the foil is rolled into position over the substrate; this keeps the patterns in perfect alignment.

We’ve noticed regular updates on this project, so it’s under active development. [Sebastián]’s most recent improvements to the setup have involved adding electronics inside the chamber, including a resistive heater to warm the substrate before deposition and a quartz crystal microbalance to measure the amount of material being deposited. We’re eager to see what else he comes up with, especially when those first chips roll off the line. Until then, we’ll just have to look back at some of [Sam Zeloof]’s DIY semiconductors.

Growing A Gallium-Arsenide Laser Directly On Silicon

February 7, 2025 by 10 Comments

As great as silicon is for semiconductor applications, it has one weakness in that using it for lasers isn’t very practical. Never say never though, as it turns out that you can now grow lasers directly on the silicon material. The most optimal material for solid-state lasers in photonics is gallium-arsenide (GaAs), but due to the misalignment of the crystal lattice between the compound (group III-V) semiconductor and silicon (IV) generally separate dies would be produced and (very carefully) aligned or grafted onto the silicon die.

Naturally, it’s far easier and cheaper if a GaAs laser can be grown directly on the silicon die, which is what researchers from IMEC now have done (preprint). Using standard processes and materials, GaAs lasers were grown on industry-standard 300 mm silicon wafers. The trick was to accept the lattice mismatch and instead focus on confining the resulting flaws through a layer of silicon dioxide on top of the wafer. In this layer trenches are created (see top image), which means that when the GaAs is deposited it only contacts the Si inside these grooves, thus limiting the effect of the mismatch and confining it to within these trenches.

There are still a few issues to resolve before this technique can be prepared for mass-production, of course. The produced lasers work at 1,020 nm, which is a shorter wavelength than typically used, and there are still some durability issues due to the manufacturing process that have to be addressed.

Schematic for progress of 3D integration. a, Schematic showing conventional 3D integration by TSV through wafers. b, M3D integration of single-crystalline Si devices by transfer, c, Growth-based M3D integration of polycrystalline devices. d, Growth-based seamless M3D integration of single-crystalline devices. (Credit: Ki Seok Kim et al., 2024, Nature)

Growing Semiconductor Layers Directly With TMDs

January 6, 2025 by 5 Comments

Transition-metal dichalcogenides (TMDs) are a class of material that’s been receiving significant attention as a possible successor of silicon. Recently, a team of researchers has demonstrated the use of TMDs as an alternative to through-silicon-vias (TSV), which is the current way that multiple layers of silicon semiconductor circuitry are stacked, as seen with, e.g., NAND Flash ICs and processors with stacked memory dice. The novelty here is that the new circuitry is grown directly on top of the existing circuitry, removing the need for approaches like TSV to turn 2D layers into 3D stacks.

As reported in the paper in Nature by [Ki Seok Kim] and colleagues (gift article), this technique of monolithic 3D (M3D) integration required overcoming a number of technological challenges, most of all enabling the new TMD single-crystals to grow at low enough temperatures that it doesn’t destroy the previously created circuitry. The progress is detailed in the paper’s schematic (pictured above): from TSV to M3D by transfer of layers and high- and low-temperature growth of single-crystal layers.

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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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