The mesa structure semiconductor was one of the earliest commercially produced solid-state electronic devices that radically changed the technological landscape. The silicon mesa transistor made commercially available by the Fairchild Semiconductor Manufacturing company is the most famous model. The mesa transistor had limitations due to its mesa-type structure and was later replaced by the planar transistor. Keep reading to find out more about the founding of the silicon mesa transistor, how it was made, and why it was later replaced by a different transistor design.
What Is a Mesa Structure Semiconductor Device?
In the natural world, a mesa is an isolated, flat-topped mountain that has steep slopes all around its boundary, and stands above its surroundings (usually a plain) distinctly. In the world of semiconductors, a mesa is a structure that has its components rising above the insulating substrate that surrounds it. The difference between them is that the mountain is typically hundreds of feet high, whereas the mesa semiconductor is less than one micron (0.001 millimeters) in height. The most famous mesa-type semiconductor device is the mesa transistor.
The Inventions That Led to the Silicon Mesa Transistor
The very first point-contact transistor was developed at Bell Labs in 1947 by scientists John Bardeen and Walter Brattain, who were led by solid-state physicist William Shockley. They utilized a block of germanium as the semiconductor with two gold point contacts. They detected a higher output current when a small positive current was applied to this system. This was essentially an amplifier. The three would later win the Nobel Prize in Physics for discovering the transistor effect and their work on semiconductors.
This new solid-state transistor technology allowed for a major difference in the miniaturization of electronics and quickly replaced the vacuum tube technology that was utilized at the time. In the years since the point-contact transistor was invented, many other types of transistors quickly sprang up. The first type of bipolar junction transistor (BJT) called the grown-junction transistor was invented by Shockley in 1948-49 and had p-n junctions. BJTs are transistors with three pins, the base, collector, and emitter.
This was the first case of doping in a semiconductor component which introduced electrons and holes as charge carriers. This used germanium as the semiconductor and it was Texas Instruments who were the first to produce a grown-junction transistor that used silicon in 1954. Further research led to the diffused junction transistor and eventually, the mesa transistor which was one step away from the planar transistor that makes nearly every type of modern electronic device work. To learn more about the chemistry and physical properties of semiconductor materials, p-n junctions, and how they work, read Understanding the Chemistry of Semiconductors.
Making Transistors: Diffusion vs Growing
The grown-junction transistor received its name from the process that created it. Here, the p-type and n-type regions of the semiconductor component are grown. The process of growing is extremely hard to control, resulting in very thick base layers. This limited the frequencies that could be used for a grown-junction transistor.
The solution to this problem was to utilize a process called diffusion rather than growing to create the doped regions of the transistor. In this, impurities were introduced into germanium and then later silicon by exposing them to high-temperature gasses that contained the dopant materials. The earliest diffusion-junction transistors had a base that was produced through the diffusion of the material into the substrate, with an emitter and collector made with alloys. When double diffusion was discovered in 1955, it was possible to form all the structures including the emitter, collector, and base. This research done at Bell Laboratories by Calvin Souther Fuller paved the way for the mesa transistor which came next.
Silicon Mesa Transistor
The IBM company’s government contracts were handled by their Federal Systems Division. Many computing requirements of the US government including administrative processing, top-secret supercomputers, and even NASA’s Apollo Space Program were fulfilled by IBM’s Federal Systems Division. The transistors that were used to build these computers were usually outsourced to companies like Fairchild Semiconductor.
Fairchild Semiconductor’s operation was located in Palo Alto which would later become famous as Silicon Valley. Their scientists Jay Last and Robert Noyce had already made advancements in photolithographic masking techniques. Aluminum properties that were required to make metal contacts were established by Gordon Moore who had even developed their own testing and manufacturing facilities.
Following the Bell Laboratories’ discoveries in double diffusion, the team at Fairchild Semiconductor was able to produce the first-ever silicon mesa transistor in 1958. As mentioned earlier, the mesa transistor is named for its raised structure that rose above the substrate. The mesa transistor was the first transistor to have diffused bases and emitters.
The mesa transistor was unveiled at the Wescon trade show in August of 1958 to much acclaim and had the technical title 2N697. While it may not sound much, this mesa transistor was selected as a component in the Minuteman ballistic missile’s guidance and control system. This was the largest defense program of the US at the time.
Mesa Transistor vs Planar Transistor
The mesa transistor like many of its predecessors had flaws. Due to the mesa structure, the collector-base junction of the mesa transistor was exposed. This made the mesa transistor very sensitive to leakage due to surface contamination. Hermetic seals were required to prevent this issue which threatened to degrade the electrical characteristics of the mesa transistor over time. This was a major reliability problem of the mesa transistor and it took a new transistor called the planar transistor to resolve it.
Planar transistors were also developed at Fairchild Semiconductor by Dr. Jean Hoerni in 1959. What he did was introduce a silicon dioxide layer to provide protection to the exposed junctions. The transistor could then be housed in affordable plastic packaging without risking contamination. While planar transistors had slower switching speeds than alloy-junction transistors, they were easier to mass produce. Planar transistors quickly advanced in the following years and became much more powerful than the models that preceded them, including the humble silicon mesa transistor.
Stepping into the Future with Semiconductors
The superior planar transistor quickly made the mesa transistor obsolete and went on to revolutionize the entire world of semiconductors. Modern integrated circuits which contain millions of microscopic transistors were only possible through these types of discoveries. The mesa transistor may have gone extinct, but it remains a crucial stepping stone in the history of semiconductor devices. To learn more about semiconductor devices, manufacturing methods, and equipment, check out our insights!
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FAQs
Semiconductors serve as the foundational materials utilized in the production of chips and integrated circuits. A chip, on the other hand, is a device constructed from semiconductor material that houses various electronic components. These components, such as transistors, resistors, capacitors, and others, are integrated to execute diverse circuit functionalities.
Various substitutes for silicon-based chips are emerging; among these, Gallium Nitride (GaN) chips stand out. GaN offers superior electron mobility compared to silicon, facilitating increased switching speed and enhanced power efficiency.
A mesa transistor is a type of diffused-junction silicon transistor that has its junction components rising above the substrate similar to the geological structure of a mesa mountain.
The mesa transistor was made commercially available in 1958 by the Fairchild Semiconductor company based in Palo Alto. It was created using the double diffusion techniques developed by Bell Labs in 1955.
