PRIORITY

This application claims the benefit of priority under 35 U.S.C. Â§119 of U.S. Provisional Application Ser. No. 61/870,419 filed on Aug. 27, 2013, the content of which is relied upon and incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to an antimony-free glass containing boron in an amount to effectively lower the glass transition temperature of the glass, a frit made therefrom, and a hermetically sealed glass packages sealed with the frit that is suitable to protect electronic devices that are sensitive to the ambient environment. Some examples of such devices are organic emitting light diode (OLED) displays, sensors, photovoltaic and other optical devices. Embodiments disclosed herein are demonstrated using OLED displays as an example.

BACKGROUND

OLEDs have been the subject of a considerable amount of research in recent years because of their use and potential use in a wide variety of electroluminescent devices, and are now reaching commercialization. For instance, a single OLED can be used in a discrete light emitting device or an array of OLEDs can be used in lighting applications or flat-panel display applications (e.g., OLED displays). OLED displays are known as being very bright and having a good color contrast and wide viewing angle. However, OLED displays, and in particular the electrodes and organic layers located therein, are susceptible to degradation resulting from interaction with oxygen and moisture leaking into the OLED display from the ambient environment. It is well known that the life of the OLED display can be significantly increased if the electrodes and organic layers within the OLED display are hermetically sealed from the ambient environment. Unfortunately, in the past it was very difficult to develop a sealing process to hermetically seal the OLED display. Some of the factors that made it difficult to properly seal the OLED display are briefly mentioned below:

The hermetic seal should provide a barrier for oxygen (10^âˆ’3cc/m²/day) and water (10^âˆ’6g/m²/day).

The size of the hermetic seal should be minimal (e.g., <2 mm) so it does not have an adverse effect on size of the OLED display.

The temperature generated during the sealing process should not damage the materials (e.g., electrodes and organic layers) within the OLED display. For instance, the first pixels of OLEDs which are located about 1-2 mm from the seal in the OLED display should not be heated to more than 100Â° C. during the sealing process.

The gases released during the sealing process should not contaminate the materials within the OLED display.

The hermetic seal should enable electrical connections (e.g., thin-film chromium) to enter the OLED display.

One method for sealing the OLED display is to use different types of epoxies, inorganic materials and/or organic materials that form the seal after they are cured, such as by irradiation. For example, some seals use a composite-based approach where alternate layers of inorganic materials and organic materials can be used to seal the OLED display. Although these types of seals usually provide good mechanical strength, they can be very expensive and there are many instances in which they have failed to prevent the diffusion of oxygen and moisture into the OLED display. Another common way for sealing the OLED display is to utilize metal welding or soldering. However, the resulting seal is not durable in a wide range of temperatures because of the substantial differences between the coefficients of thermal expansions (CTEs) of the glass plates and metal in the OLED display.

More recently, glass-based frits have been used to seal glass substrate plates in a glass package that provides excellent hermeticity to the enclosed device. But many of these frits contain toxic elements, such as antimony, which pose environmental hazards. Accordingly, there is a need for a glass-based frit suitable for hermetically sealing glass packages, such as electronic devices (e.g. for display-type applications), having a low coefficient of thermal expansion (CTE) that does not contain antimony.

SUMMARY

The present disclosure describes an antimony-free glass, a frit comprising the antimony-free glass and an hermetically sealed OLED display and method for manufacturing the hermetically sealed OLED display. Basically, an hermetically sealed OLED display is manufactured by providing a first glass substrate plate and a second glass substrate plate and depositing the frit onto the second glass substrate plate. An organic material, such as those used in the manufacture of an OLED may be deposited on the first substrate plate. An irradiation source (e.g., laser, infrared light) is then used to heat the frit which melts and forms a hermetic seal that connects the first glass substrate plate to the second glass substrate plate and also protects the OLEDs. The frit is an antimony-free glass that includes vanadium, and possibly a CTE lowering filler, such that when the irradiation source irradiates the frit, the frit is heated, softens and forms a bond between the substrate plates while avoiding thermal damage to the OLEDs. Vanadium phosphate frits, for example, have proven especially suitable for sealing glass packages of the type just described, and in particular antimony-containing vanadium phosphate frits. Such frits are stable, exhibit high optical absorbance and have excellent mechanical and aqueous durability. Unfortunately, antimony is a toxic element, and efforts have been directed toward finding a replacement for antimony that does not detrimentally affect the other beneficial attributes of the frit.

To that end, the excellent aqueous durability performance of Sb-vanadium phosphate frits was maintained without Sb₂O₃by replacement of the antimony oxide by a combination of Fe₂O₃+TiO₂, along with a small addition of ZnO to maintain flow performance and B₂O₃to reduce the glass transition temperature of the glass. The presence of Fe₂O₃was found to have the greatest effect in improving durability. However, it raised T_g, thus degrading frit flow during sealing. In addition, frits with high Fe₂O₃levels (equal to or greater than about 25 mole %) tended to be oxidatively unstable, with repeat samples fired to the same schedule (425Â° in N₂) exhibiting different colors (brown or black), with marked differences in the degree of flow. Although TiO₂alone actually degraded aqueous durability to some extent, the combination of Fe₂O₃+TiO₂+B₂O₃proved to be an ideal combination from the standpoint of obtaining laser-sealable frits with both high aqueous durability and low T_g(â‰¦365Â° C.).

Both lab bench tests exposing the glass to 90Â° C. deionized water as well as 85Â° C./85% relative humidity (RH) environmental chamber testing of laser-sealed samples indicate that frits based on the V₂O₅â€”P₂O₅â€”Fe₂O₃â€”TiO₂â€”ZnOâ€”B₂O₃system are capable of forming a low Tg frit that provides excellent sealing properties.

The antimony-free glass may contain V₂O₅in any amount in the range from â‰§40 mole % to â‰¦52.5 mole % where the upper and lower limits of suitable ranges fall therein, for example from â‰§40 mole % to â‰¦50 mole %, from â‰§40 mole % to â‰¦48 mole %, from â‰§42 mole % to â‰¦50 mole %, from â‰§42 mole % to â‰¦52.5 mole %, or from â‰§42 mole % to â‰¦48 mole %.

The antimony-free glass may contain P₂O₅in an amount from â‰§20 mole % to <25 mole %, from â‰§20 mole % to <24 mole %, from â‰§20 mole % to <23 mole %, or from â‰§20 mole % to <22.5 mole %.

The antimony-free glass may contain Fe₂O₃in an amount from >0 mole % to <25 mole %, from â‰§10 mole % to â‰¦20 mole %, from â‰§10 mole % to â‰¦18 mole %, from â‰§10 mole % to â‰¦16 mole %, from â‰§10 mole % to â‰¦15 mole %, or from â‰§10 mole % to â‰¦14 mole %.

The antimony-free glass may contain TiO₂in an amount from >0 mole % to <25 mole %, from â‰§5 mole % to â‰¦20 mole %, from â‰§5 mole % to â‰¦18 mole %, from â‰§5 mole % to â‰¦15 mole %, or from â‰§10 mole % to â‰¦18 mole %.

The antimony-free glass may contain ZnO in an amount from â‰§0 mole % to â‰¦10 mole %, from â‰§2 mole % to â‰¦5 mole %, from â‰§0 mole % to â‰¦4 mole %, or from â‰§2.5 mole % to â‰¦5 mole %.

The antimony-free glass may contain B₂O₃in an amount from >0 mole % to â‰¦20 mole %, from >0 mole % to â‰¦15 mole %, from >0 mole % to â‰¦10 mole %, from >0 mole % to â‰¦7.5 mole %, from â‰§1 mole % to â‰¦20 mole %, from â‰§3 mole % to â‰¦20 mole %, or from â‰§5 mole % to â‰¦15 mole %.

TiO₂+Fe₂O₃may be in a range from 15 mole % to 30 mole %, while TiO₂+Fe₂O₃+B₂O₃may be in a range from 25 mole % to 35 mole %, and in some embodiments TiO₂+Fe₂O₃+B₂O₃may be in a range from 27.5 mole % to 35 mole %.

Accordingly, as disclosed herein, an antimony-free glass is described comprising:

- V₂O₅â‰§40 mole % and â‰¦52.5 mole %;
- P₂O₅â‰§20 mole % and <25 mole %;
- ZnOâ‰§0 mole % and â‰¦10 mole %;
- Fe₂O₃>0 mole % and <25 mole %;
- TiO₂>0 mole % and <25 mole %;
- B₂O₃>0 mole % and â‰¦20 mole %; and
  wherein TiO₂+Fe₂O₃is in a range from 15 mole % to 30 mole %.

The antimony-free glass may, for example, comprise:

- V₂O₅â‰§40 mole % and â‰¦52.5 mole %;
- P₂O₅â‰§20 mole % and <25 mole %;
- ZnOâ‰§0 mole % and â‰¦5 mole %;
- Fe₂O₃â‰§10 mole % and <20 mole %;
- TiO₂>2 mole % and <20 mole %;
- B₂O₃â‰§1 mole % and â‰¦20 mole %; and
  wherein TiO₂+Fe₂O₃is in a range from 15 mole % to 30 mole %.

In some examples, the antimony-free glass may comprise:

- V₂O₅â‰§40 mole % and â‰¦50 mole %;
- P₂O₅â‰§20 mole % and <25 mole %;
- ZnOâ‰§2 mole % and <5 mole %;
- Fe₂O₃>0 mole % and <20 mole %;
- TiO₂>0 mole % and <20 mole %;
- B₂O₃â‰§3 mole % and â‰¦20 mole %; and
  wherein TiO₂+Fe₂O₃is in a range from 15 mole % to 30 mole %.

In other examples, the antimony-free glass can comprise:

- V₂O₅â‰§40 mole % and â‰¦50 mole %;
- P₂O₅â‰§20 mole % and <25 mole %;
- ZnOâ‰§2 mole % and <5 mole %;
- Fe₂O₃>0 mole % and <25 mole %;
- TiO₂>0 mole % and <25 mole %;
- B₂O₃>5 mole % and â‰¦20 mole %; and
  wherein TiO₂+Fe₂O₃is in a range from 15 mole % to 30 mole %.

The antimony-free glass may, for example, comprise the following composition:

- V₂O₅40 mole %;
- P₂O₅20 mole %;
- ZnO 5 mole %;
- Fe₂O₃>7.5 mole % and <15 mole %;
- TiO₂>7.5 mole % and <15 mole %;
- B₂O₃>5 mole % and â‰¦20 mole %; and
  wherein TiO₂+Fe₂O₃is â‰§15 and â‰¦30 mole %.

In other examples, the antimony-free glass may comprise the following composition:

- V₂O₅47.5 mole %;
- P₂O₅â‰§20 mole % and <22.5 mole %;
- ZnO 2.5 mole %;
- Fe₂O₃>12.5 mole % and <17 mole %;
- TiO₂>2.5 mole % and <9.5 mole %;
- B₂O₃>1 mole % and â‰¦15 mole %; and
  wherein TiO₂+Fe₂O₃is â‰§15 and â‰¦26.5 mole %.

The antimony-free glass can have a T_gâ‰¦365Â° C., such as a Tgâ‰¦350Â° C.

In some embodiments, the antimony-free glass may be a component in a frit for sealing together glass articles, such as glass plates in order to form, for example, a glass package. The frit may further comprise a CTE lowering filler, such as Î²-eucryptite or Î²-quartz.

In some embodiments of the antimony-free glass, TiO₂+Fe₂O₃+B₂O₃may be in a range from 25 mole % to 35 mole %.

In some embodiments of the antimony-free glass, TiO₂+Fe₂O₃+B₂O₃may be in a range from 27.5 mole % to 35 mole %.

In another embodiment discloses herein a glass frit is disclosed comprising:

- V₂O₅â‰§40 mole % and â‰¦50 mole %;
- P₂O₅â‰§20 mole % and <25 mole %;
- ZnOâ‰§0 mole % and â‰¦10 mole %;
- Fe₂O₃>0 mole % and <25 mole %;
- TiO₂>0 mole % and <25 mole %;
- B₂O₃>0 mole % and â‰¦20 mole %; and
  wherein TiO₂+Fe₂O₃is in a range from 15 mole % to 30 mole %.

In certain examples, TiO₂+Fe₂O₃+B₂O₃may be in a range from 25 mole % to 35 mole %.

In some examples, the glass frit further comprises a CTE-lowering filler such as Î²-eucryptite or Î²-quartz.

In another aspect, a glass package is described comprising a first glass plate, a second glass plate and a frit that connects the first glass plate to the second glass plate and forms an hermetic seal therebetween, the frit including an antimony-free glass comprising:

- V₂O₅â‰§40 mole % and â‰¦50 mole %;
- P₂O₅â‰§20 mole % and <25 mole %;
- ZnOâ‰§0 mole % and â‰¦10 mole %;
- Fe₂O₃>0 mole % and <25 mole %;
- TiO₂>0 mole % and <25 mole %;
- B₂O₃>0 mole % and â‰¦20 mole %; and
  wherein TiO₂+Fe₂O₃is in a range from 15 mole % to 30 mole %.

In some embodiments of the glass package TiO₂+Fe₂O₃+B₂O₃may be in a range from 25 mole % to 35 mole %.

In some embodiment of the glass package TiO₂+Fe₂O₃+B₂O₃may be in a range from 27.5 mole % to 35 mole %.

The glass package may further comprise an organic material disposed between the first and second glass plates. For example, the glass package may include an organic light emitting device such as an organic light emitting diode.

The invention will be understood more easily and other objects, characteristics, details and advantages thereof will become more clearly apparent in the course of the following explanatory description, which is given, without in any way implying a limitation, with reference to the attached Figures. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional illustration of the sealing of an exemplary OLED device using a frit according to embodiments of the present invention;

FIG. 2 is a plot of coefficient of thermal expansion (CTE) as a function of the substitution of Fe₂O₃for TiO₂in an Sb-free frit according to embodiments of the present invention in mole % where Fe₂O₃+TiO₂is between 20 mole % and 35 mole %;

FIG. 3 is a plot comparing CTE as a function of temperature for an Sb-free frit according to embodiments of the present invention and an Sb-containing frit under both heating and cooling conditions;

FIG. 4 is a photograph of the supernatant after temperature and humidity exposure of boron-containing antimony-free glasses compared to an antimony-containing glass;

FIG. 5 is a graph of glass transition temperature of both antimony-containing and antimony-free glasses as a function of B₂O₃concentration;

FIGS. 6 and 7 are photographs of the supernatant after temperature and humidity exposure of various compositions of boron-containing antimony-free glasses as disclosed herein;

FIG. 8 is a top-down view of a portion of a glass package showing a seal made with a frit comprising a boron-containing antimony-free glass as disclosed herein.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one having ordinary skill in the art, having had the benefit of the present disclosure, that the present invention may be practiced in other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods and materials may be omitted so as not to obscure the description of the present invention. Finally, wherever applicable, like reference numerals refer to like elements.

FIG. 1 depicts a cross-sectional side view illustrating the sealing of the basic components of a hermetically sealed OLED display 10. OLED display 10 includes a multilayer sandwich of a first glass substrate plate 12, one or more OLEDs 14, frit 16 and a second glass substrate plate 18. OLED display 10 comprises hermetic seal 18 formed from frit 16 that protects OLEDs 14 located between the first glass substrate plate 12 and the second glass substrate plate 18. Hermetic seal 20 is typically located around the perimeter of OLED display 10. OLEDs 14 are located within a perimeter of hermetic seal 20. The composition of frit 16, and more particularly the composition of the glass of frit 16, as well as how the hermetic seal 20 is formed from frit 16 is described in greater detail below.

In one embodiment, first and second substrate plates 12 and 18 are transparent glass plates. Frit 16 is deposited along the edges of second glass substrate plate 18. For instance, frit 16 can be placed approximately 1 mm away from the free edges of the second glass substrate plate 18. In the preferred embodiment, frit 16 is a low temperature antimony-free glass frit containing vanadium to enhance the optical absorbance of the frit. Frit 16 may also include a filler material, such as beta eucryptite or beta quartz, that lowers the coefficient of thermal expansion (CTE) of the frit so that it matches or substantially matches the CTEs of the two glass substrate plates 12 and 18.

OLEDs 14 and other circuitry are deposited onto second glass substrate plate 18. The typical OLED 14 includes an anode electrode, one or more organic layers and a cathode electrode. However, it should be readily appreciated that other environmentally sensitive components can be deposited onto second glass substrate plate 18.

Optionally, frit 16 can be pre-sintered to first glass substrate plate 12 prior to sealing glass substrates 12 and 18 together. To accomplish this, first substrate plate 12 comprising frit 16 deposited thereon is heated in a furnace or oven so that it becomes attached to the first glass substrate plate 12.

Next, first and second glass substrate plates 12 and 18 are brought together with frit 16 with one or more OLEDs positioned between them, and frit 16 is irradiated by irradiation source 22 (e.g. a laser or an infrared lamp) so that the frit 16 forms hermetic seal 20 that connects and bonds first substrate plate 12 to second substrate plate 18. Hermetic seal 18 also protects OLEDs 14 by preventing oxygen and moisture in the ambient environment from entering into the OLED display 10.

It should be readily appreciated that the irradiating wavelength should be within the band of high absorption in the particular frit 16. For instance, Ytterbium (900 nm<Î»<1200 nm), Nd:YAG (Î»=1064 nm), Nd:YALO (Î»=1.08 Î¼m), and erbium (Î»â‰ˆ1.5 Î¼m) CW lasers can be used depending on the optical properties of the particular frit 16 and glass substrate plates 12 and 18.

It should also be noted that most traditional low temperature sealing frits are PbO-based, because PbO frits have good flow, and adhesion properties. However, the antimony-free frits disclosed herein not only have a lower CTE than PbO-based frits, but also possess better aqueous durability, as well as being comparable to the traditional Pb-based frits with respect to adhesion.

In addition, although the role played by P₂O₅in a successful sealing frit is important, since it permits stable glasses to be formed, from a laser-sealing and post-seal performance standpoint the effect of Sb₂O₃and V₂O₅should not be ignored. In previous testing, seals made with Sb-free, Zn-based vanadium-phosphate frits could only survive the relatively benign environment of 60Â° C./40% relative humidity (RH), while seals made from mixed Sbâ€”Zn vanadium phosphate frits survived 60Â° C./85% RH before failing. Conversely, only seals made with Sb-vanadium-phosphate frits survived 85Â° C./85% RH exposure. However, despite the role that Sb₂O₃plays in improving aqueous durability, feedback from potential customers consistently raise concerns about its presence. Moreover, Sb₂O₃is thought to impede achieving desirably low glass transition temperatures (Tg). Thus, recent emphasis has been placed on development of a glass suitable for a sealing frit that is more environmentally friendly, noting that antimony is a toxic element.

Work on Sb₂O₃-free compositions began by first expressing a basic OLED device sealing frit composition as a three component system (20 mole % Sb₂O₃-50 mole % V₂O₅-30 mole % P₂O₅), simplifying the composition to a two component Sb₂O₃-free system (either 50 mole % V₂O₅-30 P₂O₅, 45 mole % V₂O₅-30 mole % P₂O₅, or 40 mole % V₂O₅-20 mole % P₂O₅), and then identifying the remaining components from the standpoint of their effect on aqueous durability, flow, glass transition temperature (T_g), and laser-sealability. Both aqueous durability, laser-sealability, and flow of any candidate frit compositions needed to be comparable to the Sb₂O₃-containing control sample, while the Tg requirements were relaxed with the criterion that T_ghad to be equal to or less than 400Â° C. (Frits with T_g>400Â° C. are unlikely to flow sufficiently during the presintering step for OLED frits to be handleable in subsequent processing.) The following oxides were investigated as potential substitutes for antimony (Sb₂O₃): WO₃, MoO₃, TeO₂, Bi₂O₃, Fe₂O₃, and TiO₂. ZnO was also investigated, although in view of the poor durability results obtained for a ZnOâ€”V₂O₅â€”P₂O₅frit, it was considered only as a minor component (5-10 mole %) to lower T_gand maintain flow. The various oxides selected were chosen on the basis that they formed stable binary glasses with V₂O₅.

All of the compositions investigated were melted, poured as glass patties, then ball-milled to form fine-particle frits (typically with a d₅₀=3-5 Î¼m). A key bench test to screen the different compositions was to prepare and fire flow buttons of the various frits, and then to assess their aqueous durability. The flow buttons were fired in N₂to 400Â° C.-450Â° C. (depending upon T_gand crystallization tendency). After firing, the flow buttons were immersed in 90Â° C. deionized water for 48 hours to assess their aqueous durability. Control samples of the OLED frit (either as the D1 base glass, or as a 70:30 by weight blend of the base glass with a Î²-eucryptite filler material) were also included in each evaluation. Of the potential replacements for Sb₂O₃that were investigated (see above), only TiO₂and Fe₂O₃appeared promising.

Listed in Tables 1 and 2 are results for a 50 mole % V₂O₅â€”30 mole % P₂O₅composition series with WO₃, MoO₃, WO₃+ZnO, Bi₂O₃, and TeO₂as the third component. Also shown are data on the standard OLED base glass, D1, as a comparison standard. All compositions (given in mole %) were evaluated for quality of glass formed from the pour, glass transition temperature (T_g) by DSC, flow and sinterability as a 3 Î¼m powder hand-pressed into a pellet (â€œflow buttonâ€ ) and fired at 400Â° C. for 1 hour in N₂, and aqueous durability (as gauged by the color of the supernatant for a fired flow button sampleâ€”the darker the color, the less durable the sample) in the bench aqueous durability test described above. Note that none of the potential Sb₂O₃replacements listed in Tables 1 and 2 produced the acceptable level of glass quality, T_g, flow, and aqueous durability exhibited by the Sb₂O₃-containing control (as judged by the appearance of the supernatant after 48 hrs, 90Â° C. deionized H₂O).

TABLE 1D1 (control)D2D3CompositionSb₂O₃, 22.9V₂O₅, 50V₂O₅, 50(molar basis)V₂O₅, 46.4P₂O₅, 30P₂O₅, 30P₂O₅, 26.3WO₃, 20MoO₃, 20Fe₂O₃, 2.4Al₂O₃, 1.0TiO₂, 1.0Glass qualityExcellentFluid, goodVery fluid,at pourqualitygood qualityT_g355Â° C.349Â° C.315Â° C.Flow (400Â°-Very goodSemi-glossy,Glossy and1 hr, N₂)flow andwell-sintered,black withsinterabilityno flowsome slumpAqueousV. slightly tintedBlackBlackdurability,appearance ofsupernatant(48 hrs, 90Â° C.D.I. H₂O)

TABLE 2D4D5D6CompositionV₂O₅, 50V₂O₅, 50V₂O₅, 50(molar basis)P₂O₅, 30P₂O₅, 30P₂O₅, 30WO₃, 10Bi₂O₃, 20TeO₂, 20ZnO, 10Glass qualityGood glass, fluid,CrystallizedMore viscous pour,at pourpoured wellafter pouringglass looked goodT_g323Â° C.Not eval.329Â° C.Flow (400Â° C.-Poor flowNot eval.Semi-glossy1 hr, N₂)black, no slumpAqueousBlackNot eval.Blackdurability

More positive results for Sb₂O₃-free vanadium phosphate frits were obtained by Fe₂O₃and/or TiO₂replacement of Sb₂O₃(see Tables 3 and 4). All compositions are expressed in mole %. Several combinations of Fe₂O₃+TiO₂produced good glasses at pouring. High TiO₂glasses (i.e., 25 mole %) such as D8 had acceptable T_gand flow properties, but also exhibited poor aqueous durabilities. Higher Fe₂O₃glasses (i.e., 25 or 30 mole %) such as D7 and D11 tended to produce poor glasses at pour, as evidenced by substantial surface devitrification. The relatively poor stability of these glasses (as indicated by the high amount of surface devitrification formed in the patty at pouring) resulted in poor flow as frits. They also tended to be unstable with respect to oxidation state, with a fired flow button from the same lot of powder alternately appearing either black (reduced) or red (oxidized) after the same firing conditions. Also included in Table 4 is D14, a glass with relatively high Fe₂O₃and TiO₂levels, but with 10 mole % ZnO to lower the expected increase in T_gfrom the Fe₂O₃. Note that a second approach to accommodating high Fe₂O₃levels is increasing the V₂O₅content. But as may be seen for D9 and D10, aqueous durability was compromised at higher V₂O₅content.

TABLE 3D7D8D9D10CompositionV₂O₅, 45V₂O₅, 45V₂O₅, 50V₂O₅, 50(molar basis)P₂O₅, 30P₂O₅, 30P₂O₅, 30P₂O₅, 30Fe₂O₃, 25TiO₂, 25TiO₂, 15TiO₂, 10Fe₂O₃, 5Fe₂O₃, 10Glass qualitySubstantialPouredPouredPouredat poursurface devitnicelynicelynicelyT_g353Â°345Â°323Â°322Â°Flow (400Â° C.,PoorlySemi-glossySintered,Sintered,1 hr, N₂)sinteredblack,some flowslight flowno slumpAqueousNotBlackMed.Med.durability,testedgreengreenappearance ofsupernatant(48 hrs, 90Â° C.D.I. H₂O)

TABLE 4D11D12D13D14CompositionV₂O₅, 42V₂O₅, 40V₂O₅, 45V₂O₅, 40(molar basis)P₂O₅, 28P₂O₅, 25P₂O₅, 25P₂O₅, 20TiO₂, 0TiO₂, 17.5TiO₂, 0TiO₂, 15Fe₂O₃, 30Fe₂O₃, 17.5Fe₂O₃, 30Fe₂O₃, 15ZnO, 10Glass qualityViscous,Good glass,Viscous,Good glass,at poursurfaceno devitsurfaceno devitdevitdevitT_g371Â°364Â°376Â°360Â°Flow (400Â° C.,Poor - powderyPoor -PoorSemi-glossy1 hr, N₂)and uncon-powderyblack,solidatedsintered,no slumpAqueousNot eval.Not eval.Not eval.Lt. browndurability

It should also be noted that although the test samples of Tables 3 and 4 having P₂O₅levels equal to or greater than 25 mole % performed poorly, it is anticipated that P₂O₅levels less than 25 mole % can be successfully employed. Table 5 summarizes the results of a second set of Fe₂O₃and TiO₂melts at 10 mole % ZnO. All compositions are expressed in mole %. As for the initial series, some combination of Fe₂O₃and TiO₂is preferred, since Fe₂O₃contributes excellent aqueous durability (but at the cost of high T_gand reduced frit sintering at 400Â°), and TiO₂results in lower T_gand improved flow (but at the cost of aqueous durability).

TABLE 5D15D16D17D18D19CompositionV₂O₅, 50V₂O₅, 50V₂O₅, 50V₂O₅, 50V₂O₅, 50(molar basis)P₂O₅, 20P₂O₅, 20P₂O₅, 20P₂O₅, 20P₂O₅, 20ZnO, 10ZnO, 10ZnO, 10ZnO, 10ZnO, 10Fe₂O₃, 0Fe₂O₃, 5Fe₂O₃, 10Fe₂O₃, 15Fe₂O₃, 20TiO₂, 20TiO₂, 15TiO₂, 10TiO₂, 5TiO₂, 0Glass qualityPouredPouredPouredPouredPouredat pournicelynicelynicelynicelynicelyT_g297Â°310Â°322Â°333Â°348Â°Flow (400Â°-Well-sintered,Well-sintered,Sintered,Sintered,Sintered,1 hr, N₂)good flowgood flowslight flowsome flowlittle flowAqueousDark blackDark blackDark blackClearCleardurability

An additional series of melts were made at higher levels of [Fe₂O₃+TiO₂] with ZnO maintained at 5 mole % (see Tables 6 and 7 below). All compositions are expressed in mole %. Note that to accommodate the higher T_gof the high Fe₂O₃glasses, flow was evaluated at 425Â° C., rather than the 400Â° C. previously used.

TABLE 6D20D21D22D23CompositionV₂O₅, 40V₂O₅, 40V₂O₅, 40V₂O₅, 40(molar basis)P₂O₅, 20P₂O₅, 20P₂O₅, 20P₂O₅, 20ZnO, 5ZnO, 5ZnO, 5ZnO, 5Fe₂O₃, 35Fe₂O₃, 30Fe₂O₃, 25Fe₂O₃, 20TiO₂, 0TiO₂, 5TiO₂, 10TiO₂, 15Glass qualitySubstantial sur-Surface devitSurface devitGood glass,at pourface + bulk devitno devitT_g416Â°407Â°400Â°389Â°Flow (425Â°-Not sinterableNot sinterableNot sinterableSintered,1 hr, N₂)at 425Â°at 425Â°at 425Â°no flowAq. durabilityNot testedNot testedNot testedClear

TABLE 7D24D25D26D27D28CompositionV₂O₅, 40V₂O₅, 40V₂O₅, 40V₂O₅, 40V₂O₅, 40(molar basis)P₂O₅, 20P₂O₅, 20P₂O₅, 20P₂O₅, 20P₂O₅, 20ZnO, 5ZnO, 5ZnO, 5ZnO, 5ZnO, 5Fe₂O₃, 17.5Fe₂O₃, 15Fe₂O₃, 10Fe₂O₃, 5Fe₂O₃, 0TiO₂, 17.5TiO₂, 20TiO₂, 25TiO₂, 30TiO₂, 35Glass qualityGood glass,Good glass,Good glass,Good glass,Good glass,at pourno devitno devitno devitno devitno devitT_g379Â°367Â°351Â°333Â°324Â°Flow (425Â°-Sintered,SinteredSintered,Sintered,Sintered,1 hr, N₂)slight flowslight flowmod. flowmod. flowgood flowAq.Clear with v.ClearMed. greenMed. greenMed. greendurabilityslight tint(residue)(residue)

As seen in previous results from Tables 1, 2 and 3, 4, Fe₂O₃levels not much higher than 20 mole % (e.g. about 25 mole %) resulted in frits with high T_g, poor stability, and unacceptable flow during 400Â° C.-425Â° C. sintering. Similarly, TiO₂not much higher than 20 mole % (e.g. about 25 mole %), resulted in frits with acceptable T_g, flow, and stability, but with unacceptable aqueous durability. Frits with Fe₂O₃levels ranging between from about 10 mole % to less than 25 mole %, and with TiO₂levels from about 15 mole % to less than 25 mole % (at 5-10 mole % ZnO) combine excellent aqueous durability with acceptable flow, T_g, and glass stability.

The aqueous durability of the (Fe₂O₃+TiO₂+ZnO) Sb₂O₃-free V₂O₅â€”P₂O₅frits were found to be comparable to or slightly superior to the Sb₂O₃-containing standard composition. An unexpected result of the Sb₂O₃-free work is that the coefficient of thermal expansion (CTE) becomes dramatically lower for the (Fe₂O₃+TiO₂+ZnO) frits at higher Fe₂O₃levels. Shown below in FIG. 2 are CTE data for sintered frits whose composition is listed in Tables 3, 4 and 5. Data are presented for all sinterable frits in the 20 mole % (Fe₂O₃+TiO₂) series of Tables 3, 4, (curve 120) and for the 35 mole % (Fe₂O₃+TiO₂) series of Table 5 as indicated by curve 122. CTE data for sintered frit bars are plotted as a function of Fe₂O₃level in each series up to 20 mole % Fe₂O₃, the apparent upper limit to achieving frits with good sinterability and oxidative stability. Note that CTE values are highest at 0 mole % Fe₂O₃/maximum TiO₂(20 mole % and 35 mole %, respectively), become essentially constant with increasing Fe₂O₃level at 60-65Ã—10^âˆ’7/Â° C., and then decrease substantially at Fe₂O₃>15 mole % (5 mole % and 20 mole % TiO₂, respectively), reaching a value of approximately 40Ã—10^âˆ’7/Â° C. at 17.5-20 mole % Fe₂O₃. By comparison, the CTE of the Sb₂O₃-containing base frit is approximately 70-80Ã—10^âˆ’7/Â° C.

A more direct comparison of CTE between the Sb₂O₃-containing and Sb₂O₃-free frits is shown in FIG. 3 where CTE curves are plotted for D1 under both heating and cooling conditions (curves 124 and 126, respectively) and D29 (remelt of D24, Table 7) also under both heating and cooling conditions (curves 128 and 130, respectively). With a CTE value of approximately 40Ã—10^âˆ’7/Â° C. for an unfilled frit, it is possible, with the addition of fillers such as Î²-eucryptite or beta quartz, to lower the CTE value of this frit close to that of fused silica.

The lab scale aqueous durability results for Sb-free frits were corroborated in a large scale sealing trial involving 85Â° C./85% RH exposure of laser-sealed samples. Shown in Table 8 are results of the trial and comparison between the standard OLED frit (D1, Table 1; used as a 70:30 blend by weight with low CTE filler Î²-eucryptite), and an Sb-free frit (D29, remelt of D24, Table 7; used as an 80:20 wt. blend with low CTE filler Î²-quartz). Each frit blend was made into a paste, dispensed on several sheets of EAGLE display glass, presintered (Sb-containing standard, heated at 325Â° C. for 2 hours in air+400Â° C. for 1 hr in N₂; Sb-free, heated at 325Â° C. for 2 hours in air+425Â° C. for 1 hour in N₂), sealed to sheets of EAGLE^XG, placed in an 85Â° C./85% relative humidity (RH) environmental chamber, and then examined periodically for evidence of seal leakage and Ca metal breakdown. In total, there were 3 sheets of the Sb-containing control composition and 7 sheets of the antimony-free composition included in the study, with 9 sealed arrays of Ca metal tabs per sheet. As may be seen in Table 8, several arrays failed either immediately after sealing or within 100 hrs of placing them in a 85Â° C./85% RH chamber for both the Sb-control and the Sb-free frits; these failures were related, most likely, to gross defects such as contamination present at random for each frit. However, after 96 hrs, no additional failures were observed for either the Sb-control or the Sb-free frit seals.

TABLE 8No. of good cellsLaser-At startAfter 96After 1056sealedof 85/85hrs of 85/85hrs of 85/85Standard Sb-frit blend27 (3252424(70:30, D1:Î²-eucryptite)sheets)Sb-free frit blend63 (7615757(80:20, D29:Î²-quartz)sheets)

In summary, the excellent aqueous durability performance of Sb-vanadium phosphate frits was maintained without Sb₂O₃by replacing the antimony oxide with a combination of Fe₂O₃+TiO₂, along with a small addition of ZnO to maintain flow and glass transition temperature (T_g). The presence of Fe₂O₃was found to have the greatest effect in improving durability. However, in large amounts it raised T_g, thus degrading frit flow during sealing. In addition, frits with high Fe₂O₃levels (equal to or greater than about 25 mole %) tended to be oxidatively unstable, with repeat samples fired to the same schedule (425Â° C. in N₂) exhibiting different colors (brown or black), with marked differences in the degree of flow. Although TiO₂actually degraded aqueous durability to some extent when added by itself, the combination of (Fe₂O₃+TiO₂) appeared to be an ideal combination from the standpoint of obtaining laser-sealable frits with both high aqueous durability and low T_g(â‰¦400Â° C.).

Both lab bench tests in 90Â° C. deionized water as well as 85Â° C./85% RH environmental chamber testing of laser-sealed samples indicate that frits based on the Fe₂O₃â€”TiO₂â€”ZnOâ€”V₂O₅â€”P₂O₅system are capable of forming a hermetic seal after laser-sealing that will withstand high humidity conditions for extended times (â‰§1000 hrs). An unexpected result of the (Fe₂O₃+TiO₂) replacement of Sb₂O₃was that the CTE of the Sb-free frit without fillers decreased by approximately half (from 70-80Ã—10^âˆ’7/Â° C. to 35-45Ã—10^âˆ’7/Â° C.), with only a minor increase in T_g(from 355Â° C. to 370Â° C.). Frits with CTE values near 40Ã—10^âˆ’7/Â° C. have the potential, with the addition of fillers such as Î²-eucryptite or Î²-quartz, of being able to seal fused silica and other low CTE substrates such as Kovarâ„¢.

However, in spite of the success in developing the foregoing antimony-free frits, the high T_g(380Â° C.) resulted in a higher pre-sintering temperature (Ëœ425Â° C.) than comparable antimony-containing frits like D1, and needed to be sustained for a longer period of time at the pre-sintering temperature. Thus, while environmentally friendly, such antimony-free frits tend to increase process times and therefore process costs. Moreover, the antimony-free frits described above were found to crystallize to at least some extent during the pre-sintering cycle, leading to somewhat reduced adhesion properties. Accordingly, additional work was conducted on a lower T_g, but still Sb-free, variant. The T_gof this newer frit, D30, was approximately 30Â° C. lower than D24, and was essentially identical to D1 in T_gand flow. This decreased T_gin D30 was achieved by incorporating about 7.5 mole % more V₂O₅at the expense of ZnO and TiO₂, indicating the role that small composition changes have on certain properties of the V₂O₅â€”P₂O₅glasses. Shown in Table 9 is a comparison between D24 and the revised composition D30. All compositional values are in mole %.

TABLE 9D24D30V₂O₅4047.5P₂O₅2022.5ZnO52.5TiO₂17.510Fe₂O₃17.517.5Al₂O₃00T_g378Â° C.351Â° C.

A key component in both D24 and D30 is Fe₂O₃, which may serve as a redox moderator of V₂O₅(as did Sb₂O₃in D1). Fe₂O₃, however, also acts to increase T_g. The other components of D24, namely ZnO and TiO₂, serve to counteract to some extent the role of Fe₂O₃in raising T_g, although they can also tend to lessen resistance to aqueous attack.

FIG. 4 shows photographs of sintered glass pellets of selected glass compositions suitable for the manufacture of glass frits in laboratory beakers for after being immersed in 90Â° C. deionized water for 48 hours. Prior to immersion the pellets were heat treated by exposing each flow button to 300Â° C. for one hour in air followed by 400Â° C. for one hour in nitrogen. FIG. 4 depicts, in order, from left to right, (a) D1, (b) D24, and (c) D30.

Although the lowering of T_gin Sb-free composition D30 to 350Â° C. was highly desirable, further composition efforts were undertaken to determine whether additional decreases in T_gwere possible. Accordingly, B₂O₃, a low T_gglass former, was added. In making the B₂O₃additions, the addition should be done in such as manner as to not degrade glass stability, aqueous durability, and flow. Indeed, the following guidelines were followed: (a) B₂O₃should not be substituted for P₂O₅, since, as noted, P₂O₅plays an important role in stabilizing the frit. When P₂O₅is present at moderate levels (approximately 20 mole %), the vanadate glass frit tends to exhibit minimal crystallization, and as a result, the frit exhibits an extended region of viscous flow during the sealing process, leading to improved adhesion; (b) B₂O₃should not be substituted for V₂O₅, since, as noted, this component is important for good flow and low CTE; (c) Fe₂O₃should be maintained as close as possible to the level (17.5 mole %) present in the starting D24 and D30 compositions, or durability could be impaired. However, small decreases in Fe₂O₃(down to about 12.5 mole %) can be tolerated with acceptable loss in aqueous durability; and (d) to maintain glass stability, the total amount of glass former (e.g., V₂O₅+P₂O₅+B₂O₃) should be at least 60 mole %, with 65-70 mole % more preferred for glass stability. With these prescriptions in mind, B₂O₃was added as follows: B₂O₃for (ZnO+TiO₂+Fe₂O₃), with Fe₂O₃maintained at â‰§12.5 mole %). It should be noted that while the following discussion is centered around D1, D24 and D30, this samples are representative of families of compositions. For example, as shown below in Table 10, each of the samples D31-D35 is a glass composition essentially the same as the D24 composition, with the exception that B₂O₃was substituted for Fe₂O₃and TiO₂in varying amounts. The same is true for Table 11, except that the glass is the D30 glass and the variations are D36-D41 (and D40 had decreased P₂O₅).

Listed below in Table 10 is the B₂O₃substitution series, including for reference D24. B₂O₃was added in an amount up to 20 mole % following the substitution schema presented above. T_gdecreased by approximately 70Â° C., from a temperature of 376Â° C. recorded for a remelt of D24 to a low of 305Â° C. for D34. The onset of crystallization is designated by T_x. All compositional values are in mole %.

TABLE 10D24D31D32D33D34D35V₂O₅404040404040P₂O₅202020202020B₂O₃057.5101520Fe₂O₃17.51513.712.5107.5TiO₂17.51513.812.5107.5ZnO555555T_g376Â° C.364Â° C.356Â° C.348Â° C.325Â° C.305Â° C.T_x(onset)497Â° C.507Â° C.506Â° C.506Â° C.511Â° C.485Â° C.

Additionally, B₂O₃substitutions were also made to D30, using the substitution schema presented earlier. B₂O₃was added in an amount up to 15 mole %. The glass transition temperature T_gfor this series decreased by approximately 50Â° C., from 351Â° C. to 299Â° C.

TABLE 11D30D36D37D38D39D40D41V₂O₅47.547.547.547.547.547.547.5P₂O₅22.522.522.522.522.522.520B₂O₃01357.51015Fe₂O₃17.517161513.512.512.5TiO₂109.58.57.56.552.5ZnO2.52.52.52.52.52.52.5T_g351Â°350Â°345Â°331Â°320Â°311Â°299Â°T_x(onset)493Â°476Â°442Â°510Â°512Â°515Â°511Â°

FIG. 5 is a graph illustrating the effect of including boron (B₂O₃) in certain frit glasses. For example, curve 200 depicts the effect on T_gfor varying amounts of B₂O₃in the general composition for D24, while curve 202 depicts the effect on T_gfor varying amounts of B₂O₃in the general composition for D30. Note that the addition of B₂O₃into these glasses resulted in a monotonic, linear decrease in T_g, indicating that no abrupt structural changes are occurring in the base vanadium phosphate glass with boron addition over the composition range studied. Equally interesting is the data represented by curve 204, wherein B₂O₃was added to the glass of D1, an antimony-containing glass. Curve 204 illustrates virtually no change in T_g, suggesting that the simple addition of boron per se may not result in a significant effect on T_g.

FIG. 6 shows photographs of sintered glass frit pellets in laboratory beakers for D24 glass, with varying amounts of B₂O₃added, after being immersed in 90Â° C. deionized water for 48 hours. The pellets were produced by forming a glass melt, grinding the solidified glass to form a glass frit, compressing the frit into pellets and sintering the pellets by exposing each pellet to 300Â° C. for one hour in air followed by 400Â° C. for one hour in nitrogen. FIG. 4 depicts, in order, from left to right, (a) 0 mole % B₂O₃, (b) 5 mole % B₂O₃, (c) 7.5 mole % B₂O₃, (d) 10 mole % B₂O₃, (e) 15 mole % B₂O₃, and (f) 20 mole % B₂O₃. Aqueous durability can be judged based on the â€œdarknessâ€ (opacity) of the supernatant: The darker the supernatant, the less durable the glass. The results shown in FIG. 6 indicate acceptable aqueous durability for B₂O₃in amounts up to about 10 mole %. It should be understood, however, that the acceptability of aqueous durability will depend on the end use of the glass.

FIG. 7 shows photographs of sintered glass pellets in laboratory beakers for D30 glass, with varying amounts of B₂O₃added, after being immersed in 90Â° C. deionized water for 48 hours. The pellets were produced as above, by forming a glass melt, grinding the solidified glass to form a glass frit, compressing the frit into pellets and sintering the pellets by exposing each pellet to 300Â° C. for one hour in air followed by 400Â° C. for one hour in nitrogen. FIG. 7 depicts, in order, from left to right, (a) 0 mole % B₂O₃, (b) 1 mole % B₂O₃, (c) 3 mole % B₂O₃, (d) 5 mole % B₂O₃, (e) 7.5 mole % B₂O₃, (f) 10 mole % B₂O₃, and 15 mole % B₂O₃. As illustrated, aqueous durability in the samples of FIG. 7 are improved over a range from about 5 mole % to about 7.5 mole %, compared with other concentrations shown.

Shown in FIG. 8 is a bright field image of a section of a laser-sealed section of two LOTUS^XTdisplay glasses 12, 18 sealed with a frit 16 made with a blend of the 5 mole % B₂O₃-modified D30 frit and a CTE-lowering glass-ceramic filler using a method as previously described in the present disclosure. The view in looking downward through glass substrate 12 to glass substrate 18. The frit connecting the glass plates includes a sealed portion 206 and unsealed portions 208. Note that the width 210 of the sealed portion of the frit, i.e. that portion of the frit actually bonded to the glass substrates, is approximately 90% of the total frit width 212 (968 Î¼m/1083 Î¼m=89.38%), indicating excellent flow and sealing behavior for a boron-containing, antimony-free frit as disclosed herein.

Sb-free frits containing boron (B₂O₃) are described for sealing electronic devices, such as OLED displays, that offer comparable-to-lower Tg and comparable-to-improved aqueous durability than current Sb-containing frits, such as represented by D1. These same boron-containing Sb-free frits also possess lower Tg and comparable aqueous durability than non-boron-containing but Sb-free frits.

Although embodiments disclosed herein have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it should be understood that these embodiments are not limited to those disclosed, but are capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the disclosure as set forth and defined by the following claims.