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Semiconductor Devices

Concepts

Semiconductor (intrinsic, extrinsic) Types (I-Type, N-Type, P-Type)

Devices

P-N Junction Diode Field-effect transistor MOSFET CMOS Integrated circuit Microcontroller Microprocessor SRAM

A microcontroller (MCU) is a microprocessor that contains a few additional components such as RAM, ROM, and programmable I/O ports primarily designed to control and drive other electronic equipment. MCUs are designed to be embedded, usually in a highly restrictive environment.

Microcontrollers, usually consume very little power, may run relatively slow, and typically execute individual task-specific programs. This is in contrast to system on chips (SoC) which are much more powerful devices, capable of executing modern-day operating systems and applications.

Overview

A PIC 18F8720 microcontroller in an 80-pin TQFP package

Microcontrollers are microprocessors with the necessary components incorporated into them to function as a single computer on a chip. This usually includes the CPU, program and data memory, programmable serial and parallel I/O ports, timers, and internal and external interrupts. External communication is a big part of microcontrollers. Because of that many MCUs allow for somewhat sophisticated I/O data manipulation programmatically.

The vast majority of microcontrollers are used in the controlling and monitoring of electronic equipment and products. Microcontrollers are designed to operate in a highly restrictive environments where characteristics such as cost, size, and power consumption are most important. MCUs range from 4-32 bits in word size and may come with as little as just a few kilobytes to a few hundred. Some MCUs can operate as low as just a few kHz and consume a few milliwatts or even microwatts in some situations. MCUs are also very cost-sensitive, ultra-cheap MCUs cost as little as just a few cents per 1000 units.

Applications

Microcontrollers are primarily designed, as their name imply, to control and drive electronic equipment. MCUs are used in a plethora of embedded systems such as toys, calculators, remote controls, power tools, office machines, and industrial controllers. More recently MCUs have found their way to implantable medical devices and internet of things. A modern home might have hundreds of embedded microcontrollers. MCUs can be found in almost all modern microwave ovens, refrigerators, dishwasher, coffee makers, and vacuum cleaners.

History

Background

Further information: MOS integrated circuit and Microprocessor chronology

The origins of both the microprocessor and the microcontroller can be traced back to the invention of the MOSFET (metal-oxide-semiconductor field-effect transistor), also known as the MOS transistor. It was invented by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959, and first demonstrated in 1960. The same year, Atalla proposed the concept of the MOS integrated circuit, which was an integrated circuit chip fabricated from MOSFETs. By 1964, MOS chips had reached higher transistor density and lower manufacturing costs than bipolar chips. MOS chips further increased in complexity at a rate predicted by Moore's law, leading to large-scale integration (LSI) with hundreds of transistors on a single MOS chip by the late 1960s. The application of MOS LSI chips to computing was the basis for the first microprocessors, as engineers began recognizing that a complete computer processor could be contained on a single MOS LSI chip.

The first multi-chip microprocessors, the Four-Phase Systems AL1 in 1969 and the Garrett AiResearch MP944 in 1970, were developed with multiple MOS LSI chips. The first single-chip microprocessor was the Intel 4004, released on a single MOS LSI chip in 1971. It was developed by Federico Faggin, using his silicon-gate MOS technology, along with Intel engineers Marcian Hoff and Stan Mazor, and Busicom engineer Masatoshi Shima. It was followed by the 4-bit Intel 4040, the 8-bit Intel 8008, and the 8-bit Intel 8080. All of these processors required several external chips to implement a working system, including memory and peripheral interface chips. As a result, the total system cost was several hundred (1970s US) dollars, making it impossible to economically computerize small appliances. MOS Technology introduced sub-$100 microprocessors, the 6501 and 6502, with the chief aim of addressing this economic obstacle, but these microprocessors still required external support, memory, and peripheral chips which kept the total system cost in the hundreds of dollars.

Development

One book credits TI engineers Gary Boone and Michael Cochran with the successful creation of the first microcontroller in 1971. The result of their work was the TMS 1000, which became commercially available in 1974. It combined read-only memory, read/write memory, processor and clock on one chip and was targeted at embedded systems.

During the early-to-mid-1970s, Japanese electronics manufacturers began producing microcontrollers for automobiles, including 4-bit MCUs for in-car entertainment, automatic wipers, electronic locks, and dashboard, and 8-bit MCUs for engine control.

Partly in response to the existence of the single-chip TMS 1000, Intel developed a computer system on a chip optimized for control applications, the Intel 8048, with commercial parts first shipping in 1977. It combined RAM and ROM on the same chip with a microprocessor. Among numerous applications, this chip would eventually find its way into over one billion PC keyboards. At that time Intel's President, Luke J. Valenter, stated that the microcontroller was one of the most successful products in the company's history, and he expanded the microcontroller division's budget by over 25%.

Most microcontrollers at this time had concurrent variants. One had EPROM program memory, with a transparent quartz window in the lid of the package to allow it to be erased by exposure to ultraviolet light. These erasable chips were often used for prototyping. The other variant was either a mask programmed ROM or a PROM variant which was only programmable once. For the latter, sometimes the designation OTP was used, standing for "one-time programmable". In an OTP microcontroller, the PROM was usually of identical type as the EPROM, but the chip package had no quartz window; because there was no way to expose the EPROM to ultraviolet light, it could not be erased. Because the erasable versions required ceramic packages with quartz windows, they were significantly more expensive than the OTP versions, which could be made in lower-cost opaque plastic packages. For the erasable variants, quartz was required, instead of less expensive glass, for its transparency to ultraviolet light—to which glass is largely opaque—but the main cost differentiator was the ceramic package itself.

In 1993, the introduction of EEPROM memory allowed microcontrollers (beginning with the Microchip PIC16C84) to be electrically erased quickly without an expensive package as required for EPROM, allowing both rapid prototyping, and in-system programming. (EEPROM technology had been available prior to this time, but the earlier EEPROM was more expensive and less durable, making it unsuitable for low-cost mass-produced microcontrollers.) The same year, Atmel introduced the first microcontroller using Flash memory, a special type of EEPROM. Other companies rapidly followed suit, with both memory types.

Nowadays microcontrollers are cheap and readily available for hobbyists, with large online communities around certain processors.

See also

• List of common microcontrollers
• List of Wi-Fi microcontrollers
• List of open-source hardware projects
• Microbotics
• Programmable logic controller
• Single-board microcontroller