Carbon nanotube-based stress sensor
An embodiment of the present invention is a technique to form stress sensors on a package in situ. A first array of carbon nanotubes (CNTs) aligned in a first orientation is deposited at a first location on a substrate or a die in a wafer. The first array is intercalated with polymer. The first polymer-intercalated array is covered with a protective layer. A second array of CNTs aligned in a second orientation is deposited at a second location on the substrate or the die. The second array is intercalated with polymer.
1. A method comprising:
depositing a first array of carbon nanotubes (CNTs) aligned in a first orientation at a first location on a substrate or a die in a wafer;
intercalating the first array with polymer;
covering the first polymer-intercalated array with a nitride layer;
depositing a second array of CNTs aligned in a second orientation at a second location on the substrate or the die; and
intercalating the second array with polymer.
2. The method of claim 1 further comprising:
calibrating stress sensors formed by the first and second polymer-intercalated arrays of CNTs.
3. The method of claim 1 wherein depositing the first array comprises:
depositing the first array of CNTs by self assembly until a desired thickness is achieved;
etching the CNTs in the first array from an undesired region using ion beam under a pre-patterned mask; and
depositing a metal contact on each end of each of the CNTs.
4. The method of claim 3 wherein depositing the metal contact comprises:
depositing a low contact resistance material by sputter deposition; and
depositing a thin line of silver paste or solder, the thin line spreading between the each of the CNTs and a metal pad.
5. The method of claim 1 wherein intercalating the first array comprises:
soaking the CNTs in a polymer solution;
precipitating polymer by solvent evaporation; and
etching a thin trench around the CNTs.
6. The method of claim 1 wherein intercalating the first array comprises:
soaking the CNTs in a solution of a monomer and a chain initiator;
polymerizing in situ the soaked CNTs; and
etching a thin trench around the CNTs.
7. The method of claim 1 wherein intercalating the second array comprises:
soaking the CNTs in a polymer solution;
precipitating polymer by solvent evaporation; and
etching a thin trench around the CNTs.
8. The method of claim 1 wherein intercalating the second array comprises:
soaking the CNTs in a solution of a monomer and a chain initiator;
polymerizing in situ the soaked CNTs; and
etching a thin trench around the CNTs.
9. The method of claim 1 wherein depositing the second array comprises:
depositing the second array of CNTs by self assembly until a desired thickness is achieved;
etching the CNTs in the second array from an undesired region using ion beam under a pre-patterned mask, the ion beam being prevented from etching the first array of CNTs; and
depositing a metal contact on each end of each of the CNTs in the second array.
10. The method of claim 9 wherein depositing the metal contact comprises:
depositing a low contact resistance material by sputter deposition; and
depositing a thin line of silver paste or solder, the thin line spreading between the each of the CNTs and a metal pad.
11. The method of claim 1 wherein depositing the second array comprises:
depositing the second array of CNTs aligned in the second orientation approximately perpendicular to the first orientation.
12. The method of claim 2 wherein calibrating comprises:
applying a known stress to the wafer in a direction approximately parallel to one of the first and second orientations; and
measuring response from the sensors based on changes in resistivity of the CNTs in the first and second arrays.