Micky Holcomb Condensed Matter Physicist West Virginia University The Physics of Faster, More Energy-Efficient Computers

Who cares about Physics? Why would one study Physics?

The Physics of Cell Phones Physics is responsible for the components in your phones and computers. The internet (formally the NSFnet*) is due to basic science funding. Memory Battery Connector Audio & Charging SIM Card Finding Signal Power Switch Camera Backup Battery GPS & WiFi Power Amplifier Runs the Screen Connection to Other Devices Keeps Time *

 Physics Helps Makes Life Better We learn about the basic products of nature and learn how to make some beefy devices.

 Computers Have Progressed

 Physics Makes Faster Computers

What is Electricity? In some materials, these electrons move freely under an applied voltage.

What is a Transistor? Resistor Transformative Changing Variable Resistor Time

Improving Transistors The number of transistors placed inexpensively on a computer chip has doubled every ~2 years (Moore’s Law) This trend has allowed massive progress in technology

Silicon A voltage on the gate electrode can induce flow of electricity between the two other contacts called the source and drain. The flow of electricity is affected by: the dielectric constant of the oxide, the area of capacitor and the oxide thickness 1) Making Them Smaller Area Speed Area Electron flow ThicknessElectron flow

Quantum Tunneling?!? Electrons are lazy! If the hill isn’t too wide, they tunnel through it. Not good.

High dielectric constant Low leakage current Works well with current Si technology Many materials have been tried but none are as cheap and easy to manipulate as existing SiO 2. 2) Replacement Oxides

3) Strain Industry found that it could improve electron travel in MOSFETs by straining (essentially squeezing) silicon. Strain can allow quicker, more efficient transfer of electrons. Strain can also affect other properties of a material.

Ex: roads, airplane wings, medical inserts, building materials Why We Care About Strain

Reaching the Limits We are reaching the limit that these strategies can continue to improve technology. 1) Scaling 2) Replacements 3) Strain

Magnetic moment electrons  4) Different Approach: Magnetism

0 0 1 Problems with Magnetic Fields Require a lot of power Heating problems Difficult to localize – limits size Magnetic field Using Magnetism

Ferroelectric Multiferroic Ferromagnetic 4) Different Approaches Spontaneous magnetization whose direction can be changed with an applied magnetic field Spontaneous polarization whose direction can be changed with an applied electric field (voltage)

P1+P1+ Bi Fe O P1-P1- 180° P4-P4- 109° P3-P3- 71° Using an electric field to change magnetism Magnetic plane is perpendicular to the polarization direction.  Electrical Control of Magnetism? Only room temperature magnetic ferroelectric (BFO)

 Physics at its Boundaries - Simple idea: Grow a magnetic material on top of a ferroelectric - BFO is not a good candidate - Problem: the physics at boundaries is not yet well understood

Magnetoelectric Interface Laser Molecular Beam Epitaxy (Laser MBE) A – Magnetic layer (LSMO) B – Ferroelectric layer (PZT) C – Substrate Programmable shutter Chu YH, et. al., Materials Today 10 (10), 16 (2007)

Visualizing the Nano 1 inch = 2.5 cm = 25 million nanometers (nm) Nanometer objects are too small to see with our eyes. We study structures that are only several nanometers in length. Scientists must use powerful microscopes to image objects this small. Penny = 0.06 inches thick (or 1,550,000 nanometers) Human hair = 100,000 nm wide

Our “Laser” Power of a laser pen: 5 mW Power of our lab’s laser: 1500 mW Paper will burn at 95 mW Femtosecond pulses, one million times smaller than nanoseconds!

Cooling Down the Physics Antarctica reaches temperatures of -129°F Capable of reaching temperatures of -450°F This is just above ABSOLUTE ZERO, the coldest possible temperature. Cryostat Other cool features: Low vibration stage Sample rotation

Measurements Elsewhere Experiments At National Labs: X-ray Dichroism Photoemission Electron Microscopy (PEEM)

Beam of electrons forced by magnets to go around in circles X-rays electrons Sample Collector X-rays excite electrons which tell us about many properties of the material electrons 150 Feet X-ray Production

As grown First E switch Second E switch Electric Control of FM

Ferroelectric Magnetic Multiferroic materials offer a pathway to new properties/devices. As computers continue to get smaller, the physics becomes more interesting. Basic physics research has allowed significant progress in computing and other modern day technologies. Magnetic and ferroelectric materials can be imaged and studied at WVU and national laboratories. Magnetic domains can be changed by an electric field. Summary

 Our Science Superheroes Left to Right: Srinivas Polisetty (post-doc), Disheng Chen (grad), Jinling Zhou (grad), Evan Wolfe (undergrad), Micky Holcomb (advisor) and Charles Frye (undergrad) National Chiao Tung University (Taiwan) A few of my collaborators: