Controlling the microstructure of poly(vinylidene-fluoride) (PVDF) thin films for microelectronics

PVDF thin films prepared under standard processing conditions have a cloudy appearance and are notoriously rough, which prevent microelectronic and photonic applications. On the other hand, high optical quality, smooth films can be prepared either at low relative humidity or at high substrate temperature. Here we systematically investigate the morphology of PVDF thin films by varying the processing conditions. Films are characterized by SEM and AFM and by measurements of clarity, haze and absorption. We show that the cloudy appearance is due to vapor-induced phase separation (VIPS) as is well-documented for the formation of PVDF membranes. Formation of opaque thin films is a general problem of any ternary polymer/solvent/non-solvent system where a high boiling point solvent is used that is fully miscible with a non-solvent, here water from the ambient.

[1]  P. Beckmann,et al.  The scattering of electromagnetic waves from rough surfaces , 1963 .

[2]  A. Fejfar,et al.  Optical absorption and light scattering in microcrystalline silicon thin films and solar cells , 2000 .

[3]  Larry R. Dalton,et al.  Polymer-based optical waveguides: Materials, processing, and devices , 2002 .

[4]  Otto J. Gregory,et al.  The influence of preparation conditions on the surface morphology of poly(vinylidene fluoride) films , 2001 .

[5]  Hideto Matsuyama,et al.  Membrane formation via phase separation induced by penetration of nonsolvent from vapor phase. I. Phase diagram and mass transfer process , 1999 .

[6]  Jan Feijen,et al.  Phase-Separation Processes in Polymer-Solutions in Relation to Membrane Formation , 1996 .

[7]  Hideto Matsuyama,et al.  Membrane formation via phase separation induced by penetration of nonsolvent from vapor phase. II. Membrane morphology , 1999 .

[8]  Marcel Mulder,et al.  Basic Principles of Membrane Technology , 1991 .

[9]  R. Zamboni,et al.  SCALING BEHAVIOR OF ANISOTROPIC ORGANIC THIN FILMS GROWN IN HIGH VACUUM , 1997 .

[10]  D. Bouyer,et al.  Morphological properties of membranes fabricated by VIPS process using PEI/NMP/water system: SEM analysis and mass transfer modelling , 2010 .

[11]  J. H. Lai.  An investigation of spin coating of electron resists , 1979 .

[12]  Vanessa F. Cardoso,et al.  Micro and nanofilms of poly(vinylidene fluoride) with controlled thickness, morphology and electroactive crystalline phase for sensor and actuator applications , 2011 .

[13]  Otto J. Gregory,et al.  The Role of Solution Phase Water on the Deposition of Thin Films of Poly(vinylidene fluoride) , 2002 .

[14]  W. Krantz,et al.  Vapor-induced phase separation—effect of the humid air exposure step on membrane morphology: Part I. Insights from mathematical modeling , 2005 .

[15]  L. Cheng,et al.  Mechanisms of PVDF membrane formation by immersion-precipitation in soft (1-octanol) and harsh (water) nonsolvents , 1999 .

[16]  P. Blom,et al.  Low voltage extrinsic switching of ferroelectric delta-PVDF ultra-thin films , 2013 .

[17]  Youn Jung Park,et al.  Spin cast ferroelectric beta poly(vinylidene fluoride) thin films via rapid thermal annealing , 2008 .

[18]  K. Yao,et al.  Crystallization mechanism and piezoelectric properties of solution-derived ferroelectric poly(vinylidene fluoride) thin films , 2006 .

[19]  Juin-Yih Lai,et al.  Insight into the preparation of poly(vinylidene fluoride) membranes by vapor-induced phase separation , 2010 .

[20]  I. Simonsen,et al.  Haze of surface random systems: An approximate analytic approach , 2009, 0904.3753.

[21]  F. Fitrilawati,et al.  Fabrication of planar waveguides of poly(N-vinylcarbazole) , 1999, International Symposium on Photonics and Applications.

[22]  R. Swanepoel.  Determination of the thickness and optical constants of amorphous silicon , 1983 .

[23]  Mengyuan Li,et al.  Revisiting the δ-phase of poly(vinylidene fluoride) for solution-processed ferroelectric thin films. , 2013, Nature materials.

[24]  K. Yao,et al.  Ferroelectric poly(vinylidene fluoride) thin films on Si substrate with the β phase promoted by hydrated magnesium nitrate , 2007 .

[25]  H. Caquineau,et al.  Influence of the relative humidity on film formation by vapor induced phase separation , 2003 .

[26]  S. Ducharme,et al.  Comparison of the theoretical and experimental band structure of poly(vinylidene fluoride) crystal , 2003 .