Electronic device having a plastic substrate

Abstract

A method of manufacturing a thin-film electronic device comprises applying a plastic coating to a rigid carrier substrate ( 12 ) using a wet casting process, the plastic coating forming a plastic substrate ( 22 ). The plastic material has a coefficient of thermal expansion greater in a first direction perpendicular to the substrate plane than in a second direction parallel to the substrate plane. Thin film electronic elements are formed over the plastic substrate and the rigid carrier substrate is released from the plastic substrate by a heating process which expands the plastic substrate preferentially in a direction perpendicular to the substrate plane. The anisotropy of the thermal expansion in the plastic substrate of the invention enables the expansion of the substrate during the thermal lift-off process to be in the perpendicular direction. This has been found to aid the lift-off process and also protect the components mounted on the upper surface of the plastic substrate.

1 . A method of manufacturing a thin-film electronic device, the method comprising:
 applying a plastic coating ( 22 ) to a rigid carrier substrate ( 12 ) using a wet casting process, the plastic coating ( 22 ) forming a plastic substrate, and comprising a transparent plastic material having a coefficient of thermal expansion at least three times greater in a first direction perpendicular to the substrate plane than in a second direction parallel to the substrate plane;   forming thin film electronic elements ( 30 ,  32 ,  34 ,  36 ,  40 ) over the plastic substrate ( 22 ); and   releasing the rigid carrier substrate ( 12 ) from the plastic substrate, by a heating process which expands the plastic substrate preferentially in a direction perpendicular to the substrate plane.   
   
   
       2 . A method as claimed in  claim 1 , wherein the plastic material has a greatest coefficient of thermal expansion in a direction substantially perpendicular to the rigid carrier substrate ( 12 ). 
   
   
       3 . A method as claimed in  claim 1  or  2 , wherein the plastic material has a least coefficient of thermal expansion in a direction substantially parallel to the rigid carrier substrate ( 12 ). 
   
   
       4 . A method as claimed in any preceding claim, wherein the coefficient of thermal expansion of the plastic material perpendicular to the rigid carrier substrate ( 12 ) is at least five times that parallel to the rigid carrier substrate ( 12 ). 
   
   
       5 . A method as claimed in  claim 4 , wherein the coefficient of thermal expansion of the plastic material perpendicular to the rigid carrier substrate ( 12 ) is at least ten times that parallel to the rigid carrier substrate. 
   
   
       6 . A method as claimed in any preceding claim, wherein the coefficient of thermal expansion of the plastic material parallel to the rigid carrier substrate ( 12 ) is less than 30·10 −6 /° C. 
   
   
       7 . A method as claimed in any preceding claim, wherein the plastic material comprises a polyimide. 
   
   
       8 . A method as claimed in  claim 7 , wherein the plastic material comprises poly(p-phenylene biphenyltetracarboximide). 
   
   
       9 . A method as claimed in any preceding claim, wherein the release is by thermally delaminating the plastic substrate from the rigid carrier substrate. 
   
   
       10 . A method as claimed in  claim 9 , wherein the thermal delamination is performed by exposure to ultraviolet laser light. 
   
   
       11 . A method as claimed in  claim 10 , wherein the ultraviolet laser light has a wavelength greater than 200 nm. 
   
   
       12 . A method as claimed in any preceding claim, wherein the rigid carrier substrate ( 12 ) comprises a glass substrate. 
   
   
       13 . A method as claimed in any preceding claim, wherein the wet casting process comprises a spin-on process. 
   
   
       14 . A method as claimed in any preceding claim, for manufacturing an active matrix display device, wherein:
 forming thin film electronic elements ( 30 ,  32 ,  34 ,  36 ,  40 ) over the plastic substrate ( 22 ) comprises forming an array of pixel circuits over the plastic substrate,   and wherein the method further comprises forming a display layer ( 100 ) over the array of pixel circuits before releasing the rigid carrier substrate from the plastic substrate.   
   
   
       15 . A method as claimed in  claim 14 , further comprising manufacturing a second substrate arrangement ( 50 ), and wherein forming a display layer over the array of pixel circuits comprises mounting the first and second substrate arrangements with electro-optic material sandwiched therebetween, the active matrix display device thereby comprising first and second substrates with the electro-optic material sandwiched therebetween. 
   
   
       16 . A thin-film electronic device, comprising:
 a plastic substrate ( 22 ) comprising a transparent plastic material, the plastic substrate having a coefficient of thermal expansion which is at least three times greater in a direction perpendicular to the substrate plane than in a direction parallel to the substrate plane; and   thin film electronic elements over the plastic substrate;   
   
   
       17 . A thin-film electronic device as claimed in  claim 16 , wherein the plastic substrate ( 22 ) has a greatest coefficient of thermal expansion in a direction substantially perpendicular to the substrate plane. 
   
   
       18 . A thin-film electronic device as claimed in  claim 16  or  17 , wherein the coefficient of thermal expansion of the plastic substrate perpendicular to the substrate plane is at least five times that parallel to the substrate plane. 
   
   
       19 . A thin-film electronic device as claimed in  claim 18 , wherein the coefficient of thermal expansion of the plastic substrate perpendicular to the substrate plane is at least ten times that parallel to the substrate plane. 
   
   
       20 . A thin-film electronic device as claimed in any one of  claims 16  to  19 , wherein the plastic material comprises a polyimide. 
   
   
       21 . A thin-film electronic device as claimed in  claim 20 , wherein the plastic material comprises poly(p-phenylene biphenyltetracarboximide).