2

Back in school I took a couple electrical engineering classes and we did a lot of Boolean math using logic gates (AND, OR, XOR, NAND, etc), but never talked about how exactly the logic in a single gate is actually implemented or made. I'm sure logic gates are much smaller than they were before. What chemicals or materials were used to create the logic for logic gates?

  • 1
    Since the 1930s? Back then it was vacuum tubes. I'm no semiconductor expert, but the transistor wasn't invented until 1947, and since then there has been a major shift from germanium to silicon. – manassehkatz-Moving 2 Codidact Aug 23 '17 at 16:49
  • Ah, thanks @manassehkatz I'll change the date. – Retro Gamer Aug 23 '17 at 17:35
3

Since the 80s? Probably not - In the 70s, there was a change from germanium to silicon in transistor technology, today, most transistors are silicon-based (although technology seems to be turning around and may be going back to Germanium in the future). That also covers about 95% of integrated circuits.

Very high-speed devices are made from GaAs substrate, and even more exotic materials, like silicon on sapphire.

So, basically, nothing has changed much during the last 30 years regarding the material chips are made from. A lot, however, has indeed changed in the process, the material used to create structures on the silicon, and, especially, in the minimum size if structures that can be created - but that would be another question.

EDIT after the question was changed:

The above covers the base materials, another thing is the doping and the creation of structures on the chip - In many cases this is something that is considered "secret magic" - chip manufacturers don't really publish this information very often. Chip manufacturing is a layering technology that consists of masking, then doping the silicone, again masking and etching structures, stacking layers and layers of semiconductor, conducting and isolating layers on top of the wafer base material.

Some selected materials:

  • Photoresist - a lacquer that is used for masking, mainly consisting of phenolic resin and a small amount of photosensitive binding agent, and obviously an organic solvent to generate proper viscosity. The photo resist also requires, once exposure and development have been done, a number of aggressive solvents to be cleaned away.
  • Silicone oxide - This is created by superheating the wafer beyond 1000°C and creates the isolating layers. In part, these oxide layers have to be etched away to create structures - As SiO2 is extremely resistive to etching, this only works with one of the most aggressive acids: fluoric acid, HFl. Nitride layers are etched using phosphoric acid (H3PO4). More modern etching procedures mix physical and a chemical processes: etching gases are "shot" at the wafer with high speed - Most of those gases are fluoride acids as well.
  • Phosphorus, arsenic and boron for doping the silicon
  • Silicon nitride and its etching by-product, ammonia, also for isolating layers
  • various forms of silicon vapour, mainly silane (SiH4) and silicon chloride (SiCH4) to create upper layer silicone structures above an isolating layer
  • Various metal vapours (Aluminium, copper, titanium and tungsten) to create conductive layers (note: modern micro chips can easily have like 10km of conducting trace on them) and dope the silicon
  • Very trivially: water. Around 4000 litres per chip as solvent and cleansing liquid
  • and lots more...

None of these would really be considered healthy chemicals, so microchip manufacturing needs huge amounts of excipients to recycle, clean, dissolve and neutralize the base and processing material. (GaAs technology is even dirtier)

| improve this answer | |
  • The question scope has changed. Your answer has not been invalidated. – wizzwizz4 Aug 23 '17 at 19:25
  • Silane is considered a N A S T Y chemical with a capital N, bold blackletter font in a curve, and background music from the band "Nasty". BTW, Silicon transistors were well established in the 1970s - planar parts (like ICs or inexpensive, plastic encased transistors) were VERY rarely made in germanium technology (only example I can think of is the AF279S transistor used in TV tuners) – rackandboneman Aug 24 '17 at 20:29
  • The nastiness of silane is not so much that it's toxic (it is), but rather that it tends to cause nice explosions when coming in contact with oxygen - You tend to explode before you're poisoned.. – tofro Aug 24 '17 at 20:48
  • Science is good in unpoisoning people these days, it lacks in unexploding people. – rackandboneman Aug 26 '17 at 13:11
  • Fun fact: Explorer 1, the third successful satellite and the US's first, had silicon transistors aboard in 1958. space.stackexchange.com/a/21961/58 That's only four years after the first working silicon transistor! – called2voyage Feb 6 '18 at 15:17
4

Logic gates can be made out of many things, including (but not limited to) metal mechanical parts (Zuse Z1), electrical relays (telephone exchanges, elevators, Z3, Harvard Mark 1), vacuum tubes (Eniac, Univac), transistors (silicon or germanium plus oxides, metal layers (Al, Cu) and doping agents, or even Lego blocks (colored plastics). There are also fluidic gates (metal or plastic channels filled with liquid or gas flows), and optical/photonic gates (glass fibers and crystals).

All of the above can be used to implement Boolean logic (NAND, NOR, etc.)

Added: Here are some drawings found on the web of how (very common in contemporary chips) MOS FET transistors can be connected to produce a single NAND or NOR logic gating function: http://www.vlsifacts.com/nand-gate-using-cmos-technology/

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.