Lecture26 transistors

Transistors

Semiconductors

A semiconductor is a material that does not conduct electricity very well

However, when some impurities are added (1 in a million atoms replaced with some other atom), they can conduct very well. When we do this, it’s called “doping”

Specially doped semiconductors only conduct one type of charge, positive (P-type) or negative (N-type). This can make their behavior unusual

For example, a diode is a P-type and N-type material in contact with eachother

Semiconductors• Function of diode is to act as a valve,

permitting the flow of current only in one direction.

• A semiconductor diode permits the flow of current from p-region to the n-region but offers a large resistance from n-region to p-region

Silicon

• A very common material and a semiconductor is silicon

• The first silicon transistor was produced by Texas Instruments in 1954, invented 1949 at Bell

• Today, most semiconductor transistors are made with silicon. Ever heard of the expression "Silicon Valley" ?

• The transistor is the key active component in practically all modern electronics. It is perhaps the most important invention of the 20th century.

The First TransistorThe workbench of John Bardeen and Walter Brattain at Bell Laboratories. They were supposed to be doing research about crystal surfaces, but the results hadn't been very good, and the company was about to cancel the project.  But in 1947 they tried very pure semiconductor material and discovered the transistor

Transitor explainedA transistor looks like two diodes back-to-back. No current should flow through a transistor because back-to-back diodes block current both ways.

True, except:

- apply a small current to the center layer of the sandwich, and a much larger current can flow through the sandwich as a whole. So, a small current can turn a larger current on and off.

Schematic of transistor

NPN and PNP Transistor Symbols

Current between collector and emitter is controlled by base.

An amplifier is a device that makes something stronger. In electrical circuits, it can be voltage, current, or both (power)

Transistors can serve as switches and/or amplifiers

Base current can be very small

Vacuum Tube

Diodes, Switches, Amps before transistors used electron beams inside an empty chamber

By having a cathode only serve as source of electrons, we make a diode (“di” meaning 2)

Vacuum TubeAdding a grid to control electron current makes a triode. With small grid voltage, can control large electron beam current – SWITCH OR AMPLIFIER

Vacuum TubeVacuum tubes were critical to the development of electronic technology, which drove the expansion and commercialization of radio communication and broadcasting, television, radar, sound reproduction, large telephone networks, analog and digital

computers

Boolean Algebra

Wich switches, we can create logic gates. Example: AND gate: if P AND Q, then true

Boolean Algebra

Wich switches, we can create logic gates. There are three main types of gates:

INPUT OUTPUT

A B A AND B

0 0 0

0 1 0

1 0 0

1 1 1

INPUT OUTPUT

A B A OR B

0 0 0

0 1 1

1 0 1

1 1 1

INPUT OUTPUT

A NOT A

0 1

1 0

AND OR NOT

Boolean Algebra

A positive-edge-triggered D flip-flop

With logic gates, can do arithmetic and store information. A “flip-flop” changes output permanently when a change occurs on the input - MEMORY

This enables COMPUTERS

You’ve heard expression: computer deals with 0 and 1. This simply refers to voltage on or off.

feedback

Computers"Computer" was originally a job title, for people: it was used to describe those human beings (mostly women) whose job it was to perform the repetitive calculations

A typical computer operation back when computers were people.

Early Computers

1822 Charles Babbage proposed steam driven calculating machine the size of a room, called the Difference Engine, to compute tables of numbers, such as logarithm tables.

Government funding for this project due to the importance of numeric tables in ocean navigation. But construction proved exceedingly difficult and the project soon became the most expensive government funded project up to that point in English history.

10 years after starting, the device was still nowhere near complete and funding dried up. The device was never finished.

Digital computers

Panel of the IBM 701 Defense Calculator, 1952

• ENIAC: Contained 18,000 Tubes, could only hold 20 numbers at a time.

• No moving parts, so it ran fast: a multiplication took 0.0028s.

• ENIAC's speed was 100,000 cycles per second. (your laptop today > 100k faster).

• The first problem run on ENIAC took 20 seconds, was checked against an answer obtained after forty hours of work with a mechanical calculator.

• Built with $500,000 from U.S. Army, ENIAC's first task: compute if it was possible to build a hydrogen bomb. After chewing this for 6 weeks, ENIAC did humanity no favor when it declared the hydrogen bomb feasible

First electronic computers used vacuum tubes.

Vacuum tubes 1.use a lot of power2.break often3.are somewhat large

Transistors enabled breakthroughFirst Microprocessor: 1971 - millions of transistors A microprocessor is a computer

that is fabricated on an integrated circuit (IC).

Computers had been around for 20 years before the first microprocessor was developed at Intel in 1971.

Intel were the first to succeed in cramming an entire computer on a single chip (IC)

Today: 42 million transistors and the 2 GHz clock rate (i.e., 2,000,000,000 times per second) used in a Pentium 4, thin chip the size of 3 x 3 cm

Microprocessors allowed very fancy calculations

1970's, you dealt with what today are called mainframe computers, such as the IBM 7090

ChipsThe progression from silicon to doped silicon to transistors to chips is what has made microprocessors and other electronic devices so inexpensive and ubiquitous in today's society.

The fundamental principles are surprisingly simple. The miracle is the constant refine-ment of those principles to the point where, today, tens of millions of transistors can be inexpensively formed onto a single chip

Power of computers: Size

45nm technology: Many critical feature sizes are smaller than the wavelength of light

In November 2006, developed a 45 nm SRAM chip with a cell size of less than 0.25 square micrometer using immersion lithography and low-k dielectrics.

The Xbox 360 S, released in 2010, has its Xenon processor (by Intel) in 45 nm process

Semiconductormanufacturingprocesses:

10 µm — 19713 µm — 19751.5 µm — 19821 µm — 1985800 nm (.80 µm) — 1989600 nm (.60 µm) — 1994350 nm (.35 µm) — 1995250 nm (.25 µm) — 1998180 nm (.18 µm) — 1999130 nm (.13 µm) — 200090 nm — 200265 nm — 200645 nm — 200832 nm — 201022 nm — 201116 nm — approx. 201311 nm — approx. 2015

Size gets you speed and larger number of circuits

Current state of computers• FLOPS (or flops or flop/s, for floating-point operations per

second) is a measure of a computer's performance

• Supercomputers are used for highly calculation-intensive tasks such as problems including quantum physics, weather forecasting, climate research, Oil and gas exploration, molecular modeling, and physical simulations (such as simulation of airplanes in wind tunnels and research into nuclear fusion)

• Currently, Japan's K computer (a cluster) is the fastest in the world, with a performance of 8.162 petaflops (1015). Six months ago, China for the first time ver had the worlds fastest computer (Tianhe-1A at 2.507 petaflops)