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Introduction to Microelectronic Circuits: Part I

6/25/2025

Jackson Anderson

Research Assistant Professor

Electrical and Biomedical Engineering

College of Engineering and Mathematical Sciences

University of�Vermont

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Table of Contents

Part 1:

What are Integrated Circuits (ICs) and why are they important?

Digital Logic Fundamentals
Moore’s Law Scaling

How are ICs made? 🡪 Process Modules

Deposition
Lithography
Etch
Doping
Oxidation & Anneal

Lab: Mask Design & Photolithography

Part 2:

Recent challenges and innovations in IC processing

Devices: 2D 🡪 3D integration
Architecture: Compute-in-memory, Analog computing
Packaging: fine pitch interconnects, interposers, integrated photonics

Lab: IC Inspection and Deprocessing

Time permitting: cleanroom window tour, examples of UVM polished samples (SEM), package inspection (microCT)

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Integrated Circuits:�Enabling personal computing

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How Computers Work – Digital Logic

All numbers can be represented in base-2 (binary), with each digit representing a power of 2

Mathematical operations can be performed just like in base-10

Each digit only has two values (1 or 0), making it easy to implement in a computer using a series of switches

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https://learn.sparkfun.com/tutorials/binary

https://technobyte.org/binary-arithmetic-rules/

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How Computers Work – Digital Logic

In binary form, logic gates can be used to combine numbers and perform mathematical operations
Half-adder:

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https://learn.sparkfun.com/tutorials/digital-logic/all

https://www.build-electronic-circuits.com/half-adder/

Carry [C]

Sum [S]

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How Computers Work: Inside Logic Gates

Logic gates performing binary operations consist of a number of switches in two states:

On or off

With transistors, there are two types of switch:

NMOS:

On [Input 1 or V_DD]
Off [Input 0 or ground/V_ss]

PMOS:

On [Input 0 or ground/V_ss]
Off [Input 1 or V_DD]

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https://learn.sparkfun.com/tutorials/digital-logic/all

https://www.geeksforgeeks.org/cmos-logic-gate/

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Dawn of Computing: Discrete Components

Electronic Numerical Integrator and Computer (ENIAC)

first general-purpose digital computer

Discrete vacuum tubes, manually programmed

Unreliable – vacuum tube replacement common

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The New York Times, Feb 15, 1946

https://www.aps.org/apsnews/2022/11/eniac-first-top-secret-program

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Solid State Electronics: The Transistor

Point contact transistor invented in December 1947 at Bell Labs

Can replace unreliable, power-hungry vacuum tubes

Planar transistor developed at Fairchild Semiconductor in 1959

Transistors now easier to integrate together on-chip

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https://www.computerhistory.org/siliconengine/invention-of-the-point-contact-transistor/

https://spectrum.ieee.org/the-silicon-dioxide-solution

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Early Integrated Circuits: IBM System/360

General-purpose computer using solid state transistors, released in 1964
Discrete transistors, mounted on ceramic substrate connecting them together

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https://www.ibm.com/history/system-360

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Early Integrated Circuits: Block II Apollo Guidance Computer

Debuted in 1966

2,800 packaged Fairchild ICs
Resistors and transistors on same chip
Two 3-input NOR gates per chip

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https://en.wikipedia.org/wiki/Apollo_Guidance_Computer

https://www.nasa.gov/the-apollo-program/

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Moore’s Law – Personal computing

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Moore, 1965 http://www.computer-architecture.org/textual/Moore-Cramming-More-Components-1965.pdf

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Modern ICs: Atomic Scale

Modern circuits have:

Over 200 Billion transistors
60+ miles of metal wiring on-chip
Layers only a few atoms thick

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Modern ICs: Personal Computing

ENIAC (1946):

$7,000,000 (2025 USD)
18,000 vacuum tubes
500 Floating point operations per second (FLOPS)
One of a kind

Apple A18 (2024 iPhone 16)

$800 MSRP
15-16 Billion transistors (est.)
>1,000,000,000,000 FLOPS
37,000,000 pre-orders

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Modern ICs: Arduino Uno

Atmel AT 35473 ATmega328 microprocessor

$22
200,000 FLOPS (https://github.com/SuperUserNameMan/arduino_flops_benchmark)
You’re programming a [1940’s] supercomputer!

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Beyond Circuits: MEMS

Digital Micromirror Devices
Inkjet Printing
Airbag Deployment
Electronic Stability Control
Portable Ultrasound
Cardiac Monitoring
Fingerprint Sensing
Precision Timing/Navigation
Wireless Communication

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IEEE MEMS @ 40

Texas Instruments

Yole Group

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Microfabrication:�How integrated circuits work

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Doping

Adding dopant atoms to semiconductor (silicon) creates more electrons or holes (lack of electron)

Allows control of conductivity 🡪 resistors
Placing differently doped semiconductors together creates barriers (depletion regions) that can be manipulated with voltage to create devices like diodes and transistors (switches)

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Doping and how diodes work:

Veritasium Blue LED: https://youtu.be/AF8d72mA41M?t=242

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Metal-Oxide-Semiconductor (MOS) Transistors

When no voltage is applied, a barrier exists between source and drain
Applying a voltage to the gate, this barrier is removed and current can flow from source to drain

Oxide under gate prevents current from flowing into gate, making an ideal switch

N-type and p-type devices can be created depending on how material is doped. When used together, this is called Complementary MOS (CMOS)

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Microfabrication:�How integrated circuits are made

Free PDF Download:

https://plummergriffinbook.stanford.edu/book

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Process Modules

Cleans – removing residue/contaminants
Deposition – adding material (thin films)
Photolithography – Patterning thin films
Etch – Removing thin films
Doping – Adding impurities to semiconductors to control electrical properties
Oxidation/Diffusion & Anneal – Growing oxides (glass), moving & activating dopants

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Cleans

Modern transistors thousands of time smaller than a human hair 🡪 Contamination control important to ensure high yield

Cleanrooms
Automated material handling systems
Chemical cleans between processing steps

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Deposition

Adatoms are delivered to the substrate surface, which nucleate into thin films using methods including

Chemical reaction of source gasses
Evaporation of source materials in a vacuum
Knocking atoms off a solid source material with a plasma (sputtering)

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Chemical Vapor Deposition

Physical Vapor Deposition

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[Photo]lithography

Uses light (UV or X-ray) to initiate a chemical reaction in a photoresist, creating a pattern when developed

Photoresist is then used to transfer that pattern into an underlying film

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Resist Develop

Film

Substrate

Photomask

UV light

Expose

Photoresist

Resist Apply

Etch or Implant

Resist Strip

Starting Wafer (Mask)

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Etch

Patterns are transferred from resist into underlying film by removing exposed materials

Physical – bombardment of wafer surface to knock atoms loose
Chemical – reaction of film with another chemical to form a byproduct that is removed

Two main types:

Wet etching – wafer dipped in chemical baths (chemical etching)
Dry etching – wafer is exposed to a plasma that contains reactive species (physical and chemical)

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Ionized species (+): Fraction ionized 10-4-10-6

Volatile byproduct

Etched films: oxide, aluminum, Si3N4 or Si

Pattering film: photo resist or oxide

Neutral species

DC electric field

Sidewall passivation

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Doping – Ion Implantation

Dopant containing gas is ionized in a plasma, certain ions are selected with a magnetic field and accelerated towards wafer
Ions collide with atoms like billiard balls and experience electronic drag force, come to rest
Beam energy, ion selection can be changed to give different dopant depths

Precise control of doping location in wafer

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Magnetic-Field pointing out of page

Measure current to determine dose

mv²/r = qvB

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Oxidation/Diffusion & Anneal

Wafers heated in tube furnace or rapid thermal process/anneal (RTA/RTP) tool to:

Oxidize silicon (grow glass [SiO2])
Heal Implant damage
Activate dopants

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Example process: RIT PMOS

PMOS only
4 mask layers

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https://gnusha.org/~nmz787/mems/unorganized/PMOS150.pdf

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Background: Mask Design and �Sunprint Lithography

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[Photo]lithography

Two activities today:

Mask Design (Klayout)

Exposure (Sunprint)

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Resist Develop

Film

Substrate

Photomask

UV light

Expose

Photoresist

Resist Apply

Etch or Implant

Resist Strip

Starting Wafer (Mask)

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Early Lithography Masks

Early mask designs done by hand 🡪 Rubylith
Modern masks are drawn in Electronic Design Automation (EDA) software

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Modern Lithography Masks

Klayout is a free, open-source EDA tool for creating IC layout files.

Each “Layer” would be manufactured into a single mask
The set of layers (mask set), together with a process flow defines an integrated circuit

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Modern Lithography Masks

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https://www.youtube.com/watch?v=X56feAtHAJ4

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Lithography Exposure

Most commercial devices use projection lithography to print features 4-5x smaller on wafer than they appear on the mask
We will use a version of a simpler process, contact lithography, today

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High Resolution

High Defectivity

Low Cost

High Throughput

Low Resolution

Low Defectivity

High Throughput

High Resolution

Low Defectivity

Lower Throughput

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Lithography Exposure

Sunprint kits include:

Photosensitive paper (“substrate” + “photoresist”)
Acrylic sheet (to hold “mask” against paper for contact print)

Today, the mask will be designed by you, using Klayout

The Sunprint activity could also use masks hand-made (a la Rubylith) from construction paper, or just use everyday objects like leaves and flowers, to adjust for different age groups

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Lab: Mask Design and Sunprint Lithography

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Layout: Connect to Virtual Votey

Log in to the lab PC
Open a web browser and go to www.desktop.uvm.edu
Log in with your temporary UVM account
Connect to “CEMS Virtual Votey” and click “Allow” for it to go fullscreen.

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Layout: Open KLayout

Open “KLayout (Editor)”

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Layout: Open KLayout

If asked, click “yes” to enable Show full hierarchy mode. This will make all shapes visible by default (bad for complex layouts, but easier for our simple layout designs)

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Layout: Create a New Layout

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Layout: Create a New Layout

Edit new layout settings to match those at right

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Layout: Set up Grid

File 🡪 Setup
Set grid to 25 um to make sure your shapes are large enough for our printer to print well.
Click Okay

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Layout: KLayout Screen

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Toolbar

Standard Cells

Cell Hierarchy (used for organizing complex layouts)

Layers

Layer Appearance

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Layout: KLayout Toolbar

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Use to select existing shapes (then press Q to edit)

Use this to draw rectangles (specify opposite corners)

Use this to add a “Text” cell, that draws text out of shapes (this prints on final layout)

Use this to draw shapes by specifying vertices

Use to move existing shapes (hold shift to move in x/y only)

Measure distances (like the dimension tool in CAD)

Boolean operation performed by drawing new shape (add to create new shapes, subtract to cut out from existing shapes)

Create text labels that don’t print on final layout (only exist in editor)

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Layout: Open KLayout

Click Layer 1/0 to select as the active layer
Click the checkbox next to Color and Stipple to expand the toolbars
Change Layer 1/0 a solid black appearance (important for printing on transparency later on)

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Layout: Your First Shape

Try selecting the Box tool, ensure you are on “add” mode, and click in the main screen
Move your mouse. You should see an outline of the box that snaps to your grid setting
Click again to define the other vertex and create the shape

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Layout: Drawing borders

Press escape to go back to the Select tool. Click on the shape you drew and press Q
In the Object Properties dialog, you can type in specific coordinates for either

The corners of your box, or
The center and x/y size of your box

Press Ok to apply the changes
If you can no longer see your shape , press F2 to zoom out

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Layout: Drawing borders

Draw four boxes to set up the borders of your layout
Press F2 to zoom out. You may also zoom in/out using the mouse scroll wheel.

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Layout: Adding your name

Find“text” in the Libraries panel (lower left. Click and drag onto the layout.
If the Editor Options opens in the toolbar, click the little window button to undock it, then click and drag on the corner to expand

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Layout: Adding your name

Click on the PCell tab and fill out the following information:

Text: Your Name
Layer: 1/0
Magnification: 100 (or greater)

Now click on the layout to place the text

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Design Away!

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Layout: Exporting your Design

Press F2 to Zoom out
Go to File 🡪 Setup 🡪 Display 🡪 Background and turn off “Show background decoration” to remove the grid for printing
Go to File 🡪 Screenshot and save an image of your design

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Exposure:

Take the exported images, paste them on a sheet (word/photoshop/inkscape) and print on transparency paper, following instructions for your printer
Cut out your mask design and follow the Sunprint instructions, using the mask as your “item.”

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