ECE 340Lecture 2 : Introduction to Semiconductor Electronics

Class Outline:

•How does a cell phone work?

Thanks to Kent Choquette, Jim Coleman and Wikipedia.

• Why look a cell phones for motivation?

• What are the major components of a cell phone?

• Which parts will we discuss more during this class?

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

Things you should know when you leave…

Key Questions

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?Let’s talk about length scales for a minute…

1 meter 1 cm 1 mm 100 µm 1 µm 100 nm10 µm 10 nm 1 nm

10-1 m100 m 10-2 m 10-3 m 10-4 m 10-5 m 10-6 m 10-7 m 10-8 m 10-9 m

10 cm

1 Hz 1 kHz 1 MHz 1 GHz 1 THz

100 Hz 103 Hz 106 Hz 109 m 1012 m

Length Scale

Frequency Scale

33 Hz

Lowest note on piano

1 kHzHighest note a

female can sing

1 ThzFrequency of

data in telecom fiber

optics

1 GHzGiga Ethernet is speed many local networks

operate

6 MHzBandwidth for

each TV channel sent down a cable

Thickness of a cellular membrane

Carbon NonotubeThickness

HIV Virus

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?Why do we care about cell phones?

• circuit board with lots of components • liquid crystal display• keyboard• microphone• speaker• battery

If you take apart cell phone, you find it contains a few parts:

It also contains:

•Optoelectronic devices•MOS devices•pn junctions

All of the devices that we will be discussing the remainder of the semester.

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?Now examine the block diagram for the cell phone…

Transmitter/Reciever

signal processing

Optoelectronics(camera, display)

Power Distribution(minimize drain on battery)

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?It contains a microprocessor unit…

Si wafer containingthousands of ICs

Integrated circuit containing millions of

transistors

cross section

singletransistor

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?The cross-section has many different layers, but why?

metal layersinterlevel

dielectric (ILD) layers

tungsten viastransistor devices

single MOS transistor

We will learn more about MOS and bipolar transistors later

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?Naturally, a cell phone contains many transistors.

Bardeen and Brattain built the first transistor in 1947.

Bardeen, Brattain, and Shockley win the Nobel Prize in 1956 for invention of the transistor

ECE & Physics faculty member atUniversity of Illinois (1952-1991)

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?But the size and performance we need doesn’t come from 1 transistor…

The Nobel Prize in Physics 2000has by The Royal Swedish Academy of Sciences been awarded

with one half jointly toZHORES I. ALFEROV

A.F. Ioffe Physico-Technical Institute, St. Petersburg, Russia and

HERBERT KROEMERUniversity of California at Santa Barbara, California, USA,

and with the other half to

JACK S. KILBYTexas Instruments, Dallas, Texas, USA.

The researchers' work has laid the foundations of modern information technology, IT, particularly through their invention of rapid transistors, laser

diodes, and integrated circuits (chips).

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?Integrated circuits allow us to miniaturize circuits…

JACK S. KILBYTexas Instruments, Dallas, Texas

BSEE University of Illinois

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

P-MOS

N-MOS

Input (A) Output (Q)

1 (Vdd) 0 (Vss)

0 (Vss) 1 (Vdd)

How does a Cell Phone Work•We can string multipletransistors together to traceout logical functionality.

•CMOS (Complementary MetalOxide Semiconductor) Logic

•Reproducible on large scales

•Leads to circuit design

•Left, we show the simpleconnection method fordifferent devices on the samewafer.

•Below, the connection schemefor a logical inverter.

Now let’s start to make something useful…

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?Gordon Moore (co-founder of Intel) made an emperical observation that the number of transistors in a integrated circuit doubles every two years…

This trend has been evident for nearly 40 years!

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?What else is there in the block diagram?

camera

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?How does the camera in the cell phone work?

sensor array

color filter array

microlensarray

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?But this isn’t the whole story, so let’s look deeper…

CMOS image sensor

sensor

control electronics, memory

1 megapixel = 1,048,576 individual sensors1,024 x 1,024 array

Each sensor is a pn photodiode (CCD) or CMOS sensor element

We will learn about photodiodes and CMOS later

Sensor yield signals in proportion to the intensity of the light

Bayer filter on a sensor

Each square of four pixels has one filtered red, one blue, and two green

The human eye is more sensitive to green than either red or blue

2009 Nobel Prize in Physics

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?Back again to the diagram…

display backlight

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How does a Cell Phone Work?We display output using a twisted nematic liquid crystal…

•Using an LC between two polarizers controls the transmission of light.

•Need a 2D matrix of LCs to create pixels with color.

Backlit display

Vert. Polarize light

LCDElectrodes for display

Glass substrate

Horiz. Polarize light

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?The LCD uses back lighting. How else can we produce light?

There are two major approaches:

• three different colors of semiconductor p-n junctions

• hybrid semiconductor/phosphor devices

Can use LEDs to generate white light very efficientlyWe will learn more about pn junctions & LEDs later

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?Henry Round made first observation of electroluminescence (1907) from SiCOleg Lossev made detailed study (1923) of electroluminescence in SiCNick Holonyak, Jr. (General Electric) demonstrated the practical GaAsP LED (1962)

Henry Joseph Round

Oleg Vladimirovich Lossev

from paper by Lossev, 1924

ECE faculty member atUniversity of Illinois

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?And now our diagram once again…

Transmitter/Receiver

digital radio

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?How does the radio work in a cell phone?

2) generate an RF sine wave with an oscillator circuit

3) mix with the information (data) in a non-linear modulator circuit

1) develop and process the baseband data signal (0100111011010)

pulse code modulation(PCM)

frequency shift keying(FSK)

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?The signal is then bounced off of towers…

Cell phones operate in hexagonal cells only a few miles apart

They can switch (handoff) cells as they move

Low power transmitters mean non-adjacent cells can reuse frequencies

Full duplex operation means pairs of frequencies are needed

full duplex – transmit and receive on different frequencies simultaneously

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?Now a bit about the history…

1946: Bell Labs launches the first commercial mobile telephone service.

At most, three subscribers per city could make calls at one time.

Each caller used a set of equipment that weighed nearly 80 pounds.

In 1947 Bell Labs was the first to propose a cellular network.

The primary innovation was a network of small overlapping cell sites in order to tracks users as they moved.

Bell Labs installed the first commercial cellular network in Chicago in 1970s.

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?The cell phone is most limited in power because it runs on batteries…

cellphone

tower

distance, r

Transmitted power, PtReceived power, PrAntenna gains, Gr, GtWavelength, λ

Free space loss

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?

Cell phone antenna gain ~ 0 dB so Gt = 1 tower antenna gain ~ 17 dB so Gr = 50Typical distance to a tower is 10 km and typical frequency, f, is 1990 MHz (f λ = c so λ = 15 cm)

remember a power ratio in dB is

For a reasonable S/N ratio (10), a typical receiver needs 50 mV at the terminals of a 50 W antenna

so Pt ~ 700 mW

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?So how long can we talk?

Assume the cell phone has an overall efficiency for transmitted power of 60%

A typical Li-ion cell phone battery is rated for 3.6 V at 1000 mA-hour

for Pt ~ 700 mW talk time will be about 3 hours

M. J. Gilbert ECE 340 – Lecture 2 08/24/1 1

How does a Cell Phone Work?How does the phone talk to the system?

Mobile Telephone Switching Office (MTSO), also called “data centers”,

where the “wireless” becomes “wired.”