Patent Description:
Electrochromic materials are materials that allow their optical and/or electrical properties to be controlled by applying a voltage. An example of a use of electrochromic materials is in electrochromic devices such as windows and mirrors, where the application of a voltage to one or more layers of EC material sandwiched between electrodes changes the transmission or reflection properties, and/or the electrical properties, of the device.

<CIT> (D1) discloses a multi-cell electrochromic device that comprises a plurality of solid-state electrochromic cells that are arranged in an optical alignment. According to D1, each electrochromic cell is separated from an adjacent electrochromic cell in the optical alignment by a transparent conductive layer that is shared by the two adjacent electrochromic cells.

<CIT> (D2) discloses an electrochromic device comprising a single cavity Fabry-Pérot filter in which the metal conductive layers forming the cavity are sandwiched by conductive dielectric layers. In another embodiment of D2, an electrochromic device comprises a dual-cavity Fabry-Pérot filter.

<CIT> (D3) discloses an all solid electrochemical device comprising at least one substrate, at least one electroconductive layer at least one electrochemically active layer capable of reversibly injecting ions, and an electrolyte, wherein the electrolyte is a layer or an inorganic, multilayer stack comprising at least one layer made of a tonically conductive material capable of reversibly injecting said ions but whose overall degree of oxidation is maintained essentially constant.

<CIT> (D4) discloses a display device comprising a plurality of independently addressable pixels comprising: a first substrate; a counter-electrode; a second substrate; a stack of electrochromic layers associated with said second substrate; an electrolyte disposed between said counter-electrode and said stack of electrochromic layers. According to D4, said electrochromic layers are each independently addressable for switching operation;
and separated from each other by layers of an electrolyte. In D2, a driving method for operating said pixel comprises the steps of: providing at least one power line which is selectively connectable to an electrochromic layer or a working electrode associated with said electrochromic layer; selectively applying to said power line a bleaching or coloring voltage; addressing the electrochromic layer which is to be bleached or colored; connecting said power line to said addressed electrochromic layer; retaining the connection of said power line during a hold period; and disconnecting said power line.

Example embodiments encompass an electrochromic (EC) cell having improved dielectric tunability and lower dielectric losses. According to the invention, the EC cell is a multi-layer electrochromic structure having a top electrode layer; a bottom electrode layer; a plurality of electrochromic layers between the top and bottom layers; a first electrolyte layer between the at least one electrochromic layer and the top layer; and a second electrolyte layer between the at least one electrochromic layer and the bottom layer.

In another embodiment, a mm-wave device with tunable capacitance includes the above mentioned multi-layer electrochromic structure and a voltage source for applying a voltage between the top electrode layer and the bottom electrode layer.

In either of the above embodiments, the plurality of electrochromic layers includes an electrochromic film layer and an ion storage film layer wherein the electrochromic film layer is between the second electrolyte layer and the ion storage film layer.

In any of the above embodiments, the electrochromic film layer and the ion storage film layer further comprise transition metal oxides and the electrochromic film layer is selected from the group consisting of tungsten tri-oxide (WO<NUM>), titanium oxide (TiO<NUM>), molybdenum trioxide (MoO<NUM>), tantalum oxide (Ta<NUM>O<NUM>) and niobium pentoxide (Nb<NUM>O<NUM>) while the ion storage film layer is selected from the group consisting of nickel oxide (NiO), chromium oxide (Cr<NUM>O<NUM>), manganese oxide (MnO<NUM>), iron oxide (FeO<NUM>), cobalt oxide (CoO<NUM>), rhodium oxide (RhO<NUM>) and iridium oxide (IrO<NUM>).

In an embodiment, the electrochromic file layer is tungsten tri-oxide (WO<NUM>) and the ion storage film layer comprises nickel oxide (NiO).

In any of the above embodiments, the electrolyte layers are an electrolyte displaying different ion and electron conductivities, for example, lithium niobate (LiNbO<NUM>).

In any of the above embodiments, the electrochromic film layer, the ion storage film layer and the first and second electrolyte layers have thicknesses between <NUM> and <NUM> micron.

The scope of protection of the invention is set out by the independent claim. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claim are to be interpreted as examples useful for understanding various embodiments of the invention.

Electrochromic (EC) materials are materials that allow their optical and/or electrical properties to be controlled by applying a voltage. EC materials are often used as one of the layers in a multi-layer structure known as an electrochromic (EC) cell. Various characteristics of an EC cell may be engineered to tailor the EC cell for a variety of applications without changing its material composition.

An embodiment of an EC cell <NUM> is shown in <FIG>. This embodiment is not according to the claimed invention. Glass (not shown) may be used as a substrate on which is formed several layers. These layers include two conducting layers <NUM> and <NUM>, at least one EC layer <NUM>, for example, a transition metal oxide, adjacent to conducting layer <NUM> and an ion-conducting or electrolyte layer <NUM> between EC layer <NUM> and either the other conducting layer <NUM> or a second EC layer <NUM>. In an embodiment, layer <NUM> is lithium niobate (LiNbO<NUM>), although any electrolyte displaying different ion and electron conductivities, typically σL > <NUM>-<NUM> S/cm for ions and σe < <NUM>-<NUM> S/cm for electrons, may be used.

In an embodiment, layers <NUM> and <NUM> are conductors, for example, gold, indium tin oxide (ITO), zinc oxide (ZnO), a conductive polymer or any material that is a good electrical conductor. Layer <NUM> is a chromic film, for example, tungsten tri-oxide (WO<NUM>), however, a variety of other transition metal oxides may be used, such as titanium oxide (TiO<NUM>), molybdenum trioxide (MoO<NUM>), tantalum oxide (Ta<NUM>O<NUM>) or niobium pentoxide (Nb<NUM>O<NUM>). Layer <NUM> is another chromic film, also understood as an ion storage film, chosen to have complementary electrochromic characteristics to chromic film layer <NUM>. Layer <NUM> may be, for example, nickel oxide (NiO), although a variety of other transition metal oxides, such as chromium oxide (Cr<NUM>O<NUM>), manganese oxide (MnO<NUM>), iron oxide (FeO<NUM>), cobalt oxide (CoO<NUM>), rhodium oxide (RhO<NUM>) or iridium oxide (IrO<NUM>).

EC cell <NUM> is actuated by applying a voltage to conductive layers <NUM> and <NUM>. This voltage is provided by, for example, voltage source <NUM>. In a non-actuated state, EC layers <NUM> and <NUM> are non-conductive and behave as insulators. Electrolyte layer <NUM> is non-conductive in both actuated and non-actuated states. Upon application of a DC bias voltage between conducting layers <NUM> and <NUM>, ions from electrolyte layer <NUM> are expelled and subsequently injected into the one or more EC layers <NUM> and <NUM> through a process of intercalation, which changes the fundamental characteristics of the EC layers.

<FIG> illustrates another embodiment of an electrochromic (EC) cell at <NUM>. This embodiment is according to the claimed invention. Top and bottom layers <NUM> and <NUM> are conductors, for example, gold, indium tin oxide (ITO), zinc oxide (ZnO), a conductive polymer or any material that is a good electrical conductor. Layer <NUM> is a chromic film, for example, tungsten tri-oxide (WO<NUM>), however, a variety of other transition metal oxides may be used, such as titanium oxide (TiO<NUM>), molybdenum trioxide (MoO<NUM>), tantalum oxide (Ta<NUM>O<NUM>) or niobium pentoxide (Nb<NUM>O<NUM>). Layer <NUM> is another chromic film, also understood as an ion storage film, chosen to have complementary electrochromic characteristics to chromic film layer <NUM>. Layer <NUM> may be, for example, nickel oxide (NiO), although a variety of other transition metal oxides, such as chromium oxide (Cr<NUM>O<NUM>), manganese oxide (MnO<NUM>), iron oxide (FeO<NUM>), cobalt oxide (CoO<NUM>), rhodium oxide (RhO<NUM>) or iridium oxide (IrO<NUM>). In an alternative embodiment of EC cell <NUM>, layer <NUM> is not present.

Layers <NUM> and <NUM> are ion-conducting layers, and form an electrolyte. In an embodiment, layers <NUM> and <NUM> are lithium niobate (LiNbO<NUM>), although any electrolyte displaying different ion and electron conductivities, typically σI > <NUM>-<NUM> S/cm for ions and σe < <NUM>-<NUM> S/cm for electrons, may be used. Layers <NUM> and <NUM> serve as a tank for providing available ions to be injected into chromic layers <NUM> and <NUM> when a DC bias voltage is applied to bottom layer <NUM> and top layer <NUM>. This voltage is provided by, for example, voltage source <NUM>. Layers <NUM> and <NUM> may both be formed from the same or different electrolyte materials.

Depending on the application, EC cell <NUM> of <FIG> may also include one or more substrates, not shown for conciseness. These substrates may be glass, for example, but any structurally stable substrates may be used.

In order to explain the operation of EC cells <NUM> and <NUM> of <FIG> and <FIG>, the diagrams of <FIG> are provided. <FIG> depicts a cross-sectional view of internal layers of EC cell <NUM> as shown in <FIG>. Although specific materials are shown, one of ordinary skill in the art would understand that the following discussion applies to any of the alternative materials for these layers as described above. In <FIG>, an ion-conducting or electrolyte layer <NUM> of LiNbO<NUM> is sandwiched between an EC film layer <NUM> of WO<NUM> and an ion storage film layer <NUM> of NiO. The total height of the layers without DC bias voltage applied to external electrodes (not shown) attached at the top and bottom of the layers <NUM> and <NUM> is given by h0V = hWO3 + hLiNbO3 + hNiO. However, when the DC bias voltage is applied, ions from layer <NUM> intercalate into layers <NUM> and <NUM>, resulting in their transition from insulators to relatively poor conductors with a resistivity of up to approximately <NUM>x<NUM>-<NUM> (cm), for values of x~<NUM>. 5in in LixWO<NUM>. As a result, from the point of view of the external electrodes, the chromic layers effectively become part of the external electrodes and the channel height of the EC cell becomes approximately hVmax = hLiNbO3.

<FIG> depicts a cross-sectional view of internal layers of EC cell <NUM> of <FIG>. In this EC cell, EC film layer <NUM> of WO<NUM> and an ion storage film layer <NUM> of NiO have been moved away from the external electrodes (not shown) into the interior of the EC cell. An ion-conducting or electrolyte layer is split into two layers <NUM> and <NUM> on either side of layers <NUM> and <NUM> at the point of contact with the external electrodes. Since the electrolyte does not exhibit a dielectric to metal transition by losing ions, the effective height of the EC cell remains the same at both 0V and Vmax as h = hLiNbO3 + hWO3 + hNiO + hLiNbO3. This provides a greater degree of dielectric tunability and lower dielectric losses, since the channel height is not shortened.

As described above, when a voltage is applied across EC cells <NUM> or <NUM>, ions from the electrolyte layer or layers intercalate into the chromic layers. The net effect of ion intercalation and de-intercalation is macroscopically observed as modulation of the dielectric characteristics of the EC cell, in particular, its dielectric constant, or relative permittivity, and its loss tangents. This modulation provides for tailoring the dielectric and the optical characteristics of the EC cells of <FIG> and <FIG> for a variety of applications.

<FIG> depicts the relative permittivity εr vs. frequency in GHz of the EC cell of <FIG>. In an actuated state (DC bias voltage = 4V), εr is shown as curve <NUM> and in a non-actuated state (DC bias voltage = 0V) εr is shown as curve <NUM>. <FIG> shows the percentage dielectric tunability for the curves of <FIG>. In an example embodiment of this EC cell, the thicknesses of the individual layers are hLiNbO3 = <NUM>, the hWO3 = <NUM> and hNiO = <NUM>. Although specific thicknesses are shown for the purposes of illustration, all three layers of the EC cell of <FIG> may vary between approximately <NUM> and <NUM> micron. As is evident from <FIG>, the EC cell of <FIG> achieves a dielectric tunability pf approximately <NUM>%.

<FIG> depicts the relative permittivity εr vs. frequency in GHz of the EC cell of <FIG>. <FIG> shows permittivity when the EC cell is in an actuated state (DC bias voltage = 4V) as curve <NUM> and a non-actuated state (DC bias voltage = 0V) as curve <NUM>. <FIG> shows the percentage dielectric tunability for the curves of <FIG>. In an example embodiment of this EC cell, the thicknesses of the individual layers are hLiNbO3 = <NUM> and hWO3 = <NUM>. Although specific thicknesses are shown for the purposes of illustration, all four layers of the EC cell of <FIG> may vary between approximately <NUM> and <NUM> micron. As is evident from <FIG>, EC cell <NUM> achieves a dielectric tunability of no less than <NUM>%.

With regard to <FIG>, <FIG>, although these figures depict example embodiments of a DC bias voltage of 4V, any voltage up to approximately <NUM> V may be used. The DC bias voltage depends on a number of factors, including thickness of the layers in the EC cell.

Each of the layers in an EC cell exhibits a capacitance, with the total equivalent capacitance of the EC cell related to the sum of the capacitances of the constituent layers. The capacitance of each layer is proportional to the dielectric permittivity. By modulating the dielectric permittivity, it is possible to change the operational characteristics of the EC cell. Thus, the EC cells described above have many applications in both the MM-wave and optical domains, for example, displays with a tailor-made optical response and beam-forming function as well as tunable optical and microwave devices, such as phase shifters, switches, attenuators and antennas.

An EC cell as described above may be fabricated using a variety of semiconductor device manufacturing processes including, for example, chemical vapor deposition (CVD) and reactive-ion etching (RIE).

Claim 1:
A multi-layer electrochromic structure (<NUM>) comprising:
a top electrode layer (<NUM>);
a bottom electrode layer (<NUM>);
a plurality of electrochromic layers (<NUM>, <NUM>) between the top and bottom electrode layers:
a first electrolyte layer (<NUM>) between the plurality of electrochromic layers and the top electrode layer (<NUM>); and
a second electrolyte layer (<NUM>) between the plurality of electrochromic layers and the bottom electrode layer (<NUM>), wherein the first electrolyte layer (<NUM>) is at a point of contact with the top electrode layer (<NUM>), and the second electrolyte layer (<NUM>) is at a point of contact with the bottom electrode layer (<NUM>).