Featured Research

from universities, journals, and other organizations

New Micro-technology Will Need To Consider Fatigue In Silicon Crystals

Date:
December 4, 2007
Source:
National Institute of Standards and Technology
Summary:
Researchers have demonstrated a mechanical fatigue process that eventually leads to cracks and breakdown in bulk silicon crystals -- a phenomenon that's particularly interesting because it long has been thought not to exist.

Optical micrographs of contact damage in silicon from cyclic stress show progressive damage after (a) 1,000 cycles, (b) 5,000 cycles, (c) 20,000 cycles and (d) 85,000 cycles. Color added for clarity, white circle shows computed size of the contact circle.
Credit: NIST

Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a mechanical fatigue process that eventually leads to cracks and breakdown in bulk silicon crystals -- a phenomenon that's particularly interesting because it long has been thought not to exist. Their recently published* results have important implications for the design of new silicon-based micro-electromechanical system (MEMS) devices that have been proposed for a wide variety of uses.

Silicon--the backbone of the semiconductor industry--is one the world's most heavily studied materials, and it has long been believed to be immune to fatigue from cyclic stresses because of the nature of its crystal structure and chemical bonds. And indeed, conventional tests have validated this. Recent research into silicon MEMS devices, however, has revealed that these microscopic systems that incorporate tiny gears, vibrating reeds and other mechanical features do seem to develop stress-induced cracks that can lead to failure.

Why this happens at the microscopic scale is a matter of debate. One school of thought holds that the effect is purely mechanical, due to friction, and the other argues that it essentially is caused by corrosion--a chemical effect. Because the effect has only been noticed at submicrometer scales, it has been difficult to determine which theory is correct.

A material's resistance to cracking--referred to as "toughness" by materials scientists--is measured customarily by taking a sample of the material, slightly notching one edge, and pulling on the ends repetitively to see if the tensile stress causes the notch to grow into a crack. Bulk silicon always has passed this test. But, argued the NIST team, in real-world MEMS devices the stresses are likely to be much more complicated.

To test this, they used an alternate method: pressing the top of test crystals with tiny tungsten-carbide spheres about 3 mm in diameter at pressures below the silicon's breaking point. Simply pressing down hard on the crystal for days at a time caused no detectable cracks--arguing against the corrosion theory. On the other hand, using half the pressure but cycling the test hundreds of thousands of times revealed a gradually increasing pattern of surface damage at the indentation site--clear indication of mechanical fatigue.

The NIST team, which included a researcher from the University of Extremadura in Spain, theorizes that the critical element in their experiments is the addition of shear stress (causing the crystal planes to slide against each other), a component missing in conventional tensile strength tests but not uncommon in real-world applications.

The NIST experiments demonstrated fatigue effects in silicon at the comparatively large scale of hundred of micrometers. The next step is to determine if the same mechanisms operate at the submicrometer level.

* S. Bhowmick, J.J. Melιndez-Martνnez and B.R. Lawn. Bulk silicon is susceptible to fatigue. Applied Physics Letters 91, 201902. Published online 13 November 2007.


Story Source:

The above story is based on materials provided by National Institute of Standards and Technology. Note: Materials may be edited for content and length.


Cite This Page:

National Institute of Standards and Technology. "New Micro-technology Will Need To Consider Fatigue In Silicon Crystals." ScienceDaily. ScienceDaily, 4 December 2007. <www.sciencedaily.com/releases/2007/11/071127153945.htm>.
National Institute of Standards and Technology. (2007, December 4). New Micro-technology Will Need To Consider Fatigue In Silicon Crystals. ScienceDaily. Retrieved August 22, 2014 from www.sciencedaily.com/releases/2007/11/071127153945.htm
National Institute of Standards and Technology. "New Micro-technology Will Need To Consider Fatigue In Silicon Crystals." ScienceDaily. www.sciencedaily.com/releases/2007/11/071127153945.htm (accessed August 22, 2014).

Share This




More Matter & Energy News

Friday, August 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Flower Power! Dandelions Make Car Tires?

Flower Power! Dandelions Make Car Tires?

Reuters - Business Video Online (Aug. 20, 2014) — Forget rolling on rubber, could car drivers soon be traveling on tires made from dandelions? Teams of scientists are racing to breed a type of the yellow flower whose taproot has a milky fluid with tire-grade rubber particles in it. As Joanna Partridge reports, global tire makers are investing millions in research into a new tire source. Video provided by Reuters
Powered by NewsLook.com
Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Awesome New Camouflage Sheet Was Inspired By Octopus Skin

Newsy (Aug. 19, 2014) — Scientists have developed a new device that mimics the way octopuses blend in with their surroundings to hide from dangerous predators. Video provided by Newsy
Powered by NewsLook.com
Researcher Testing on-Field Concussion Scanners

Researcher Testing on-Field Concussion Scanners

AP (Aug. 19, 2014) — Four Texas high school football programs are trying out an experimental system designed to diagnose concussions on the field. The technology is in response to growing concern over head trauma in America's most watched sport. (Aug. 19) Video provided by AP
Powered by NewsLook.com
Green Power Blooms as Japan Unveils 'hydrangea Solar Cell'

Green Power Blooms as Japan Unveils 'hydrangea Solar Cell'

AFP (Aug. 19, 2014) — A solar cell that resembles a flower is offering a new take on green energy in Japan, where one scientist is searching for renewables that look good. Duration: 01:29 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins