Counter electrode for an electrochromic device
An imaging system for a portable electronic device includes a variable aperture between a lens group and an image sensor. The variable aperture is defined by an electrochromic stack that defines a switching region and a central non-switching region. The electrochromic stack is defined by a layer of electrochromic material in which an electrochromic crystallite dispersion (e.g., nickel oxide) is suspended in a field of a lithiated ion conductor layer (e.g., lithiated tungsten nickel oxide).
1 . A stack capable of defining at least a portion of an electrochromic layer of an imaging system in a portable electronic device, the stack comprising:
an optically transparent substrate;
a metal oxide layer disposed onto the optically transparent substrate; and
a precursor layer disposed onto the metal oxide layer to a first thickness, the precursor layer capable of defining an electrochromic counter electrode of the electrochromic layer of the imaging system when annealed, the precursor layer comprising a lithiated transition metal oxide stack defined by alternating layers of a first transition metal oxide and a second transition metal oxide; wherein:
the first transition metal oxide is nickel oxide;
the second transition metal oxide is tungsten oxide or tantalum oxide;
each layer of first transition metal oxide is disposed to a second thickness; and
each layer of second transition metal oxide is disposed to a third thickness.
2 . The stack of claim 1 , wherein the second thickness is greater than the third thickness.
3 . The stack of claim 1 , wherein the second thickness is approximately equal to the third thickness.
4 . The stack of claim 1 , wherein the first thickness is selected at least in part to optimize for optical transparency.
5 . The stack of claim 1 , wherein the optically transparent substrate is formed from silica glass and the metal oxide layer comprises indium tin oxide.
6 . A method of forming an anneal precursor stack and a counter electrode of an electrochromic layer of an imaging system in a portable electronic device, the method comprising:
forming the anneal precursor stack by:
selecting an optically transparent substrate;
disposing a first metal oxide layer onto a surface of the optically transparent substrate;
forming a precursor layer, to a first thickness, over the metal oxide layer by alternatingly disposing:
a second thickness of a first transition metal oxide over an uppermost layer of the precursor layer; and
a third thickness of a second transition metal oxide over the uppermost layer of the precursor layer; wherein lithium ions are diffused to a selected concentration within at least one of the first transition metal oxide or the second transition metal oxide;
annealing the anneal precursor according to an anneal plan to cause the precursor layer to define the counter electrode comprising a diffusion of crystallites of the first transition metal oxide suspended in a field of lithiated second transition metal oxide;
dispose a second metal oxide layer over the counter electrode; and
etch at least one of the first metal oxide layer or the second metal oxide layer to define a switching region and a non-switching region of the counter electrode, wherein:
the first transition metal oxide is nickel oxide; and
the second transition metal oxide is tungsten oxide or tantalum oxide.
7 . The method of claim 6 , wherein the first metal oxide layer and the second metal oxide layer comprise indium tin oxide.
8 . The method of claim 6 , wherein forming the precursor layer is performed at least in part by a planetary deposition process in which the optically transparent substrate is rotated through at least a first deposition region in which the first transition metal oxide is disposed and a second deposition region in which the second transition metal oxide is disposed.
9 . The method of claim 6 , wherein the anneal plan comprises instructions for annealing the precursor layer at approximately 450° C. for a selected time period.
10 . The method of claim 6 , wherein the anneal plan comprises instructions for setting a temperature of the anneal precursor during deposition of the precursor layer.
11 . The method of claim 6 , wherein an average crystallite diameter of the diffusion of crystallites is approximately 5 nm.
12 . The method of claim 6 , wherein at least one of the first transition metal oxide or the second transition metal oxide are disposed by one of:
chemical vapor deposition;
sputtering; or
evaporation.
13 . The method of claim 6 , wherein the second thickness is ranges between and including 20% and 200% of the third thickness.
14 . A method of forming an anneal precursor stack to define a counter electrode of an electrochromic layer of an imaging system in a portable electronic device, the method comprising:
disposing a first metal oxide layer onto a surface of a substrate;
forming a precursor layer, to a first thickness, over the metal oxide layer by alternatingly disposing:
a second thickness of a first transition metal oxide over an uppermost layer of the precursor layer; and
a third thickness of a second transition metal oxide over the uppermost layer of the precursor layer; and
annealing the anneal precursor according to an anneal plan to cause the precursor layer to define the counter electrode comprising a diffusion of crystallites of the first transition metal oxide suspended in a lithiated material, wherein:
the first transition metal oxide is nickel oxide; and
the second transition metal oxide is tungsten oxide or tantalum oxide.