DIY Transistors: Tools Needed to Build Transistors from Zero

I saw some amateur DIY transistors on the Internet, such as Neil Steiner and Jim. Among them, the most noticeable home-made transistor comes from a craftsman Jeri Ellsworth who understands the physics of semiconductor components. She built a small manufacturing facility (or fab) at home in 2010 and produced some simple circuits using homemade chips.

Interestingly, no other complete record of DIY transistor data can be found after that. This may be because this type of manufacturing inevitably leads to the handling of some hazardous chemicals and it will take several years to complete (Jeri spent 2 years). Furthermore, since transistors are building blocks for manufacturing electronic products, they can be purchased at a very cheap price and can also be used to create more complex ICs that can perform functions directly.

However, it is said that if transistors can be created from scratch in their own laboratories, it is a great achievement for amateurs. We can imagine the personal satisfaction created by our own transistors.

Today, most fabless companies outsource their actual production overseas because after investing US$10 billion in building advanced manufacturing plants, if more engineers and technicians are to be employed to operate the plant and equipment, they must face it. The cost of recurrent expenditure is too high. Most companies are unable to maintain the required sales volume for this huge financial investment.

Because there are no other alternatives that can produce transistors at a lower cost, these overseas foundries have also written sales records of US$400 billion and have taken one vote. Basically, while huge manufacturing facilities do cause cost and technical hurdles, it may make more sense to explore easier-to-use modular transistor manufacturing (especially prototypes).

For example, Jeri Ellsworth and Neil Steiner use prefabricated germanium diodes and cadmium sulfide photocells to make transistors, respectively. This differs from the way that transistors are constructed only with bare crystals because diodes and photocells are pre-manufactured.

The tools needed to build transistors from scratch are not common tools in home labs. Here are some less common tools:

• Nitrogen tank

• Furnaces

• Hydrofluoric acid (HF)

• Phosphosilicate film

• Prime grade silicon wafers

• Vinyl sticker replaces photomask photoresist

• Color table to identify oxide thickness

Some of these materials may be more harmful than others. Any person using HF must be very careful because this chemical may penetrate the tissue and cause very serious burns. A nitrogen tank is not necessary, but it helps to control the gas pressure in the furnace, making it easier to predict the growth of oxide layers on the silicon, and it can save even more when growing thin layers that are only a few hundred angstroms (A) thick. More time. In addition, it is worth noting that doped pure silicon is another development plan, so it may be more feasible to purchase pre-doped Prime grade silicon crystals on the network. Other amateur equipment also includes power supplies, oscilloscopes, tweezers, CPU fans, conductive epoxy and solders.

How to make a transistor?

Transistors are manufactured by optical lithography. Basically, the substrate surface is patterned to form various transistor topologies. This is a topological structure of a metal oxide field effect transistor (MOSFET), as shown in the following figure. Show.

Similarly, this large p-type substrate is easily available online.

It takes some time to grow the initial oxide layer in the kiln. For example, Jeri said it takes about 6 hours to grow a 500-600-A thick oxide layer. It is not necessary to pull out the ultra-small caliper and the microscope when measuring its thickness, because its color is obvious to see the thickness. A 600-A thick thin layer corresponds to green.

To achieve a specific pattern, the oxide can be etched or removed by using HF. For many etching steps, a portion of the wafer can be protected from etching by “etching” the material against etching. Vinyl sticker masks can be pre-cut to resist etchant in certain areas.

The source and drain regions are created by rotating the phosphosilicate film onto the chip so that there is a thin layer of liquid on the wafer; this is usually done using a CPU fan.

The assembly was again placed in a kiln at 1000°C for a period of time to deposit a high concentration of phosphorous onto the surface of the substrate and the oxide layer - resulting in two doped n-type regions, eventually forming an electronic channel flow.

Finally, a vinyl mask is used to etch away the gate area and put it back into the kiln to grow the gate oxide layer. Jeri specifies a thickness of 800 to 1,000 A—approximately pink to dark red.

The contacts with the gate, source, drain, and substrate can be made of conductive epoxy. This is accomplished by etching with another vinyl mask and more so that the access point is brought down to the source and drain, and an epoxy that can be soldered to the wire is placed.

This is explained in more detail in other different websites. Obviously, the complexity of this process will increase exponentially as we design reticle and plan multi-transistor topologies. The size and scope of the task may become larger and more difficult to handle. Therefore, manufacturing an electric chip with a gate width down to nanometer scale requires a large-scale manufacturing facility and a CAD program for laying out millions of transistors.