Mechanical property measurement of thin films by micro plane-strain compression
This invention is directed to the measurement of stress-strain relationships in thin films using substantially flat, parallel test surfaces with minimal width. This invention is further directed to the measurement of stress-strain relationships in thin films at controlled temperatures and at high strain rates above 100% per second.
1. A testing apparatus for determining the stress-strain relationship in a film comprising:
(a) a first and a second substantially flat test surfaces between which the film is placed for testing, the flat test surfaces each having a substantially linear configuration and in substantially complete alignment and wherein the width of each test surface is at least equal to the thickness of the film and no greater than twice the thickness of the film;
(b) a position means for positioning the test surfaces substantially parallel to each other;
(c) a displacement means for moving one of the test surfaces with respect to the second test surface; and
(d) a thermal control means for modulating temperatures of the film and the test surfaces comprise a heating surface and a cooling surface having a thermoelectric component positioned between said surfaces;
wherein the position means for positioning at least one of the test surfaces is a double cantilever structure onto which one test surface is attached.
2. The apparatus of claim 1 , wherein the displacement means for moving one of the test surfaces with respect to the second test surface is capable of delivering a displacement velocity to the test surfaces to achieve a strain rate ranging from 10 0 to 10 4 (100% to 1,000,000%) per second.
3. The apparatus of claim 1 further comprising an insulation means.
4. The apparatus of claim 1 , wherein the thermal control means is capable of generating a temperature at the test surfaces in a range from −50° C. to +150° C.
5. The apparatus of claim 1 , wherein the thermal control means is capable of generating a temperature at the test surfaces in a range from −50° C. to 0° C.
6. The apparatus of claim 1 wherein each test surface has a surface variation of less than about 30 nm.
7. The apparatus of claim 6 wherein each of the test surface comprises a single crystal.
8. The apparatus of claim 7 wherein at least one of the test surfaces consists essentially of silicon.
9. A method for determining the stress-strain relationship in a film of comprising the steps of:
(a) placing the film between a first and a second substantially flat test surfaces for testing, the flat test surfaces each having a substanstially linear configuration and wherein the width of each test surface is at least equal to the thickness of the film and no greater than twice the thickness of the film;
(b) positioning the test surfaces substantially parallel to each other;
(c) modulating temperatures of the film and the test surfaces by a heating surface and a cooling surface of thermal control means having a thermoelectric component postioned between said surfaces;
(d) moving one of the test surfaces toward second test surface to compress the film; and
(e) measuring the force required to compress the film;
wherein the test surfaces are positioned substantially parallel by means of a double cantilever structure onto which one test surface is attached.
10. The method of claim 9 , wherein the temperatures at the test surfaces is modulated to a range from −50° C. to +150° C.
11. The method of claim 9 , wherein the temperatures at the test surfaces is modulated to a range from −50° C. to 0° C.
12. The method of claim 9 , wherein each test surface has a surface variation of less than about 30 nm.