electronic materials and applications€¦ · • high throughput (combinatorial) materials science...

Combinatorial Approaches to Functional Materials 5/5-6/2014 M. L. Green

Electronic Materials and Applications

Martin L. Green, NIST


Computing Power Has Increased By A Factor of 107 Since 1970


The cost of developing new materials, and the time for commercializing them can both be decreased through simulation and modeling, which are less expensive and faster than experimentation

The Materials Genome Initiative

A large portion of the MGI program thus far has been devoted to modeling, simulation, and curation of data

High throughput (combinatorial) experimentation is the counterpart to the concerted computational materials design efforts being carried out under MGI

Such experimentation will realize the MGI approach by:

Enabling rapid experimental verification of models and simulations, iteratively improving them

Generating the data needed to power the MGI “engine” and thereby enable new models


Combinatorial Materials Science • High throughput (combinatorial) materials science methodology is

a relatively new research paradigm that has enabled rapid and efficient materials discovery, screening, and optimization

• MGI will be an important driver of high throughput methodologies for ongoing materials innovations in substitutes for critical materials, functional materials, energy-related materials, catalysts, materials discovery, etc. • Major challenges: – Expense and availability of high throughput facilities – Novel high throughput metrologies (fast and local) will be

needed – Real time data collection and analysis – Managing large amounts of data in a variety of formats – Better materials informatics


Why Now?: e.g., Increasing Complexity of Si Technology

Courtesy of Intel Corp.


The Advanced Gate Stack

Source

Silicon substrate

Gate Metal Electrode

Drain

Lc

Wc

High-κ Gate Dielectric

HfO2, Hf-O-N, Hf-Si-O, higher-κ…..

Metals, alloys, nitrides, silicides…..

Thermal and electrical stability of

the interfaces

2005 ITRS: ...The crux of this problem comes from the fact that the traditional transistor…materials, silicon, silicon dioxide, and polysilicon have been pushed to fundamental material limits and continued scaling has required the introduction of new materials.


HT Work Flow and Equipment Needs • Library synthesis tool (usually specific to a

few classes of materials) ($1.0M) • Basic characterization tools (composition,

structure) (generic to many classes of materials) ($1.5M)

• HT metrology (usually specific to one or two classes of materials) ($0.2M)

• Data analysis/informatics capability (generic to many classes of materials) ($0.2M)


• When I first visited Sematech in 2004, they had not heard of combinatorial materials science

• Found about 40 references • Lots of proprietary research


Silicon substrate

Gate Metal

Drain

Lc

Wc

High-κ gate dielectric

HfO2, ZrO2, Y2O3, Al2O3, silicates, aluminates, ...

nitrides, alloys, silicides…..

Candidates:

Candidates:

Thermal and electrical stability of the interfaces

Source

Metal-oxide-semiconductor field effect transistor (MOSFET) Motivation – Gate Metal Electrode

Challenge: For novel gate metal electrodes, need to know work function

Problem: Many candidates for gate metal electrode; not feasible to look at them all on a one-at-a-time basis


Strategy Ta1-xAlxNy/HfO2/Si gate stack

Ta1-xAlxNy library film

50 nm

p-Si

HfO2 (3 nm)

SiO2 (4, 5, 6, or10 nm)

Side View

Identical Ta1-xAlxNy composition spreads were deposited on four different thickness of dielectric layers using a shadow mask. These four libraries allow us to systematically extract work functions.

Vfb vs. EOT is used to extract Φm

We use an automated probe to measure capacitance – voltage (C-V) characteristics of hundreds of MOS capacitors for each library.

Over 2000 MOS capacitors are measured.

TaNy

AlNy

Top View


Capacitors: Ta1-xAlxNy Library

100 µm

Each capacitor has a different metal gate

composition

Chang et al, IEEE TRANS. ELECT. DEV., VOL. 55, NO. 10, 2008


TaN Ta1-xAlxN

4.4

4.5

4.6

4.7

4.8

4.9

5

5.1

5.2

5.3

0 10 20 30 40 50 60 Composition (x)

Wor

k fu

ncti

on (

eV)

HfO2(3nm)+SiO2(4, 5, 6, 10nm)

HfO2(3nm)+SiO2(4, 5, 6, 10nm) 900°C, 5s, Ar

Extracted Work Functions from the Ta1-xAlxN Library

Alshareef et al, APL, 88, 072108 2006

• Represents two years effort for a postdoc • Many other projects can go on simultaneously • Almost all tools are multi-use


Thermoelectric materials can generate an electrical potential from a thermal gradient, and vice-versa.

• The Seebeck Effect: The conversion of a temperature differential directly into electricity.

S = Seebeck coefficient = - ∆V/∆T

Major Application: Vehicular waste heat recovery

• The Peltier Effect: When a current flows through the junction of dissimilar materials, heat will either be absorbed or evolved depending on the direction of current flow.

Q = Heat current = Π x I (Π = Peltier coefficient, I = electrical current) Major Application: Solid-state refrigeration

• ZT is the figure of merit of thermoelectric

materials performance • Good candidate thermoelectric materials

exhibit high electrical conductivity and low thermal conductivity (unfortunately in most materials they are correlated)

0 T

C PPMS

Screening tool

Thermoelectric Materials


Pulsed laser deposition growth of a ternary thermoelectric material

library

(Ca2Sr)Co4O9

Ca3Co4O9 (Ca2La)Co4O9

Si(100) substrate

Thermoelectric System (Ca-Sr-La)3Co4O9

Otani et al, APL 91, 132102 (2007)


Thermoelectric Materials

M. Otani et al., APL 2007

Comparison of Seebeck coefficients

measured by scanning tool and

commercial (single measurement) tool


Material Measurement Laboratory

Phase Transformation in VO2

Tetragonal (Rutile), IR reflective Monoclinic, IR transparent

Eyert, Ann.Phys. 2002 Dimerization.

T = 68°C

e- density, c-axis compressive stress

To depress transformation temperature by impurity atoms:

increased e-density, dope with larger atoms.

For W impurities: 20°C/at.%



Thermochromic ‘Smart’ Windows

win

dow

: co

ld d

ay

win

dow

: ho

t da

y

outd

oors

indo

ors

outd

oors

indo

ors

At T < Tc, solar heating desirable, and window is VIS/NIR transparent.

At T > Tc, window is VIS transparent and NIR reflective.

VIS

NIR VIS/NIR

VIS/NIR



High Throughput Reflectometry

Thermochromic phase transition in V1-xNbxO2 Monoclinic Tetragonal

Measure NIR reflectance at many temperatures and locations (compositions)

35 temperatures X 165 locations

= 5775 spectra in 20 hours

x = 0.014


High Throughput Combinatorial Library Analysis: V-W-Nb-O

Combinatorial Thin Film Library

X-ray diffraction

Material Property Characterization: Thermochromism in VO2 region

Manual Analysis

High Speed Clustering Analysis

-20 0 20

-20

0

20

Structure-Property Relationship

VO2

WOx NbOx

electronic materials and applications€¦ · • high throughput (combinatorial) materials science...

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