On Thursday, I will be back on Bryan Crump’s radio show (Nights, Radio New Zealand National, 8.42pm, Thursday July 15th). This week, we will continue our discussion of transistors, several billion of which are currently helping you read this article. Last time, we talked about how quantum mechanics allows transistors to work as electronic switches. This week, Bryan wants to discuss how transistors became so embedded in so many of the technologies we rely on in the modern world, and what exactly they are doing there!
A valley of silicon?
Although the idea had been around since the 1920s, the first transistor was made by John Bardeen and Walter Brattain at Bell Labs in New Jersey in 1947. It was made out of germanium, a semiconducting material similar to silicon, and was about the size of something you might put on your mantelpiece.
However, it was their boss, William Shockley, who tried to commercialise the transistor.
Bell Labs has been credited with pretty much inventing the modern world (just take a look at this list of its inventions). It has been criticised, however, for stifling the commercialisation of its inventions. Indeed, Shockley didn’t get an opportunity to try to turn a buck from the transistor at Bell Labs. Rather, he founded Shockley Semiconductor Laboratory on the opposite coast of the US: in Mountain View, California.
Why there? Well, the San Francisco Bay area already had a healthy electronics industry, which supplied components to the US military. This meant that there was a supply of skilled electronics workers. Nearby Palo Alto was home to Stanford University, which had set up the Stanford Industrial Park to encourage the development of high-tech industries such as Hewlett-Packard in the region. And importantly, Palo Alto was also home to William Shockley’s aging mother.
Silicon Valley was born.
Putting together a team of talented physicists and engineers, Shockley immediately set to work on developing silicon transistors. But Shockley was a terrible manager. Within a few years, Shockley Semiconductor was haemorrhaging its best young staff, including Gordon Moore (of ‘Moore’s Law’), who would later go on to co-found Intel. The firm was not well placed to react to the invention of the integrated circuit by Texas Instruments in Dallas in 1958.
The integrated circuit revolutionised the manufacture of electronics. Instead of making individual components, like transistors, separately, and then assembling them one by one on a circuit board, Jack Kilby developed a multi-step technique to fabricate the components and the circuit on a sheet of germanium all in one go. This tremendously sped up mass production, and led to cheap, light-weight electronic devices.
However, a Bay Area company that had been founded by disgruntled Shockley employees was not far behind Texas Instruments in making integrated circuits. In fact, Robert Noyce at Fairchild Semiconductor produced the first silicon integrated circuit six months after Kilby. And in the end, it was Noyce’s design that prevailed.
The military-industrial complex
From its invention until the mid-1960s, the Apollo program and the US military bought almost every integrated circuit built. Costs fell dramatically as production volumes increased and companies like Fairchild began to outsource to Asia.
By the end of the decade, however, pressures on the US military budget meant that the gravy train began to dry up, and the semiconductor industry had to develop new consumer markets. Today, you’ll find integrated circuits in cell phones, computers, and many other digital appliances.
So how are integrated circuits made? The process, known as photolithography, is actually a bit like taking a photograph using film.
The layout of the circuit is defined by a light shining it through a cut-out template, known as a mask, onto a wafer of silicon. The wafer will be covered in film of light sensitive chemicals called photo resist, which ‘cure’ when exposed to light. Regions that are shaded by the template don’t undergo this curing process, and chemical treatments can then be used to etch these regions away, engraving a pattern defined by the template into the silicon wafer underneath the resist.
I like traffic lights
So what can be done with a circuit full of transistors?
In my previous article on transistors, I explained that a transistor is an electronic switch: the current that flows through a transistor is turned on and off by applying a voltage at what is called its ‘gate’.
Transistors can be assembled into logic devices. A traffic light is a type of logic device, for instance: if the light is green light is on, the red light should be off. We could ensure this always happened using just a single transistor.
Imagine we set up the circuit that supplies electricity to the red light so that it can be short-circuited by a transistor. The transistor will now act as an inverter: the red light will switch on when the transistor is off but will switch off when the transistor is on.
Now by allowing the transistor to be switched on and off by the circuit that supplies current to the green light, then we ensure the red light will never be on when the green light is on.
More complicated logic operations can be performed if we assemble more transistors. If we have traffic lights running north-south and east-west, we could use the transistor that shorts the north-south red light to switch a transistor that short-circuits the green east-west light. Thus, when the north-south green light is on, it switches off the east-west green light and so on …
Unless your cell phone is modelled on something out of the original Star Trek, it probably doesn’t work by switching red and green lights off and on. Rather, it is adding and multiplying many, many ones and zeroes (’ons’ and ’offs’) using arrays of transistors assembled for the purpose.
Today, of course, Silicon Valley is a hub not only for electronics, but also for software and biotechnology. This is partly due to the fact that those early semiconductor companies not only invented the integrated circuit, but being far from the traditional sources of finance on the east coast, also had to pioneer the modern venture capital industry. William Shockley’s decision to set up in Mountain View and his subsequent mismanagement had far reaching implications indeed.