Directly patterning ferroelectric films by nanoimprint lithography with low temperature and low pressure

1
Directly patterning ferroelectric films by
nanoimprint lithography with low temperature and
low pressure

• K.C. Hsieh and H.L. Chien
• Department of Materials Science and Engineering,
  National Taiwan University, Taipei, Taiwan
• C.H. Lin
• National Nano Device Laboratories, Hsinchu,
  Taiwan
• C.Y. Lee
• Department of Materials Science and Engineering,
  National Taiwan University, Taipei, Taiwan
• Journal of Vacuum Science Technology B 24(6).
  Nov/Dec 2006, p3234-3236.

Joanne Yim EE C235/NSE C203
2
Outline

• Background
• Why ferroelectric materials?
• Conventional nanoimprint lithography
• Direct nanoimprint on metals
• Method
• Gel precursor
• Au/gel bilayer
• Results
• Summary/Questions Remaining

3
Why ferroelectric materials?

• Apply electric field to induce electric dipole
  moment
• Used for
• Memory, sensors, actuators, optoelectronics
• Large-area patterns
• Examples BaTiO3, PbZrTiO3

4
Conventional NIL

• Shape, then harden some soft material into relief
  of desired pattern
• Transfer pattern to substrate by etching
• Processing speed/resolution limited by etching

5
Direct nanoimprint previously

• Semiconductor material
• Excimer laser-assisted
• Requires high power and high pressure
• Metal films
• 100MPa
• Imprinted onto soft film
• DIRECT shape material, not some buffer
• Must be malleable
• Use sharper mold to reduce pressure

6
Method 1

• MOD (metal organic decomposition) solution of
  Pb(Zr0.52Ti0.48)O3 with excess Pb
• Spin coat 200nm onto Si substrate
• 120C anneal to remove solvent, make gel
  maximize hardness difference
• Si mold apply at RT, 10-20MPa
• Dry _at_ 120C, pyrolyze _at_ 450C, anneal _at_ 650-800C
  to obtain perovskite phase
• (higher T anneal more complete perovskite
  structure)

7
Method 2

• FE require some metal contact to apply electric
  field
• Apply metal thin film and shape along with FE
  layer
• Better
• Less sticking
• Less relaxation after mold release

8
Results FE gel

• After imprint, features 60nm high, much less
  than 500nm mold height and gel depth
• gel sticks to mold

9
Results FE gel Au film

• Depth by AFM
• 14MPa (top) 90nm
• 20MPa 300nm

10
Summary/Questions remaining

• Malleable precursor can be directly imprinted
• Combining with top metal film improves transfer
• Thickness of Au film?
• When will cracking begin?
• Applicability to other material systems?