Student Creates First Homebrew Dual Differential Amplifier IC

Making your own DIY integrated circuits was considered a near-impossible feat, especially when you factor in all the equipment and tools needed for the lithography process. Most makers don’t have a high-temperature furnace, vacuum chambers or an electron microscope on hand to fabricate ICs as that equipment can (and often is) more expensive than some used cars. Those issues though, haven’t stopped high school student Sam Zeloof from building a fab shop in his garage and creating his own dual differential amplifier IC.

Zeloof began building his garage-based fab roughly a year ago after pondering how to make his own chips and what’s involved in the process of creating them, which led him to read old books and patents on the subject. He then found Jeri Ellsworth’s YouTube videos where she detailed how to build home-brew silicon transistors and replicated the process using materials and broken equipment (he repaired himself) he acquired on eBay.

Zeloof designed his Z1 amplifier IC using Magic VLSI to create a 4 mask PMOS- active/doped area, gate oxide, contact window and top-metal, all with a 16:9 aspect ratio. To pattern his circuit onto a silicon wafer, he modified a digital video projector by adding a miniaturizing optical lens, thereby enabling him to create a mask using the digital image. With his garage-based setup, Zeloof could create doped features at a resolution of about 1.5μm without the need of creating physical masks.

In his blog, Zeloof goes over every detail of the Z1 design process, including all 66 steps needed for its fabrication along with the lithography process details. When the process is complete, he uses an electron microscope to check for any abnormalities the chips may have acquired during the fabrication phase. Once the chip passes muster, he then physically tests them by probing the wafer with either sharp tweezers or utilizing a flip-chip board (he doesn’t own a wire bonder) connected to a curve tracer. It’s also undergoes testing in-circuit to verify operation.

Since starting the blog in 2017, Zeloof has gotten a lot of positive feedback, including some advice and tips from engineers who are veterans of circuit design. As far as the future goes, Zeloof is looking to develop a straightforward process for making his Z1 chip and perhaps make small batches of them for the maker community.