WO2013067081A1

WO2013067081A1 - Microwave sealing of inorganic substrates using low melting glass systems

Info

Publication number: WO2013067081A1
Application number: PCT/US2012/062901
Authority: WO
Inventors: Srinivasan Sridharan; John J. Maloney; Chandrashekhar S. Khadilkar; Robert P. Blonski; Gregory R. PRINZBACH; George E. Sakoske
Original assignee: Ferro Corporation
Priority date: 2011-11-02
Filing date: 2012-11-01
Publication date: 2013-05-10
Also published as: EP2773596A1; CN103906718A; JP6527613B2; EP2773596A4; US20140261975A1; EP2773596B1; RU2014110540A; JP2015505792A; RU2638993C2; JP2018108929A; DK2773596T3; CN108455880A

Abstract

A frit-based hermetic sealing system for sealing glass plates to one another, or sealing glass to ceramics is disclosed. Seal materials, the methods to apply these seal materials, and the seal designs for selective and controlled absorption of microwave energy to heat and seal the system are presented. The hermetic seals are useful in various applications such as (a) encapsulating solar cells based on silicon, organic systems, and thin film, (b) encapsulating other electronic devices such as organic LEDs, (c) producing Vacuum Insulated Glass windows, and (d) architectural windows and automotive glass.

Description

MICROWAVE SEALING OF INORGANIC SUBSTRATES

USING LOW MELTING GLASS SYSTEMS

BACKGROUND OF THE INVENTION

1. Field of Invention

[0001] The present invention relates to a frit-based hermetic sealing system for sealing glass plates to one another, or sealing glass to ceramics, the seal materials, the methods to apply these seal materials, and the seal designs for selective and controlled absorption of microwave energy to heat and seal the system. These hermetic seals are useful in various applications such as (a) encapsulating solar cells based on silicon, organic systems, and thin film, (b) encapsulating other electronic devices such as organic LEDs (OLED), (c) producing Vacuum Insulated Glass (VIG) windows, and (d) architectural windows and automotive glass.

2. Description of Related Art

[0002] In many practical applications of glass to glass sealing, such as encapsulation of solar cells (crystalline silicon as well as thin films based CdTe and CIGS, polymeric, flexible), OLED packaging, displays, touch screens, vacuum insulated glass (VIG) windows sealing, and architectural and automotive windows sealing, there exists a need to use tempered glasses in many instances. Tempered glasses lose their temper when heated above about 300 °C in conventional furnace firing of sealing glass materials. Therefore, there exists a need to selectively heat the seal material alone and to effect the bonding to the base glasses/substrates without significantly heating the base glasses/substrates.

[0003] Accordingly, improvements in the art of selective sealing methods such as microwave sealing are required.

BRIEF SUMMARY OF THE INVENTION

[0004] From the universe of various selective heating techniques such as IR heating, induction heating, microwave heating, laser sealing, and high density plasma arc lamp sealing, microwave heating offers heating rates up to 1000°C/sec (compared to 6 to 10° C/sec slow heating of glass in conventional ovens) coupled with excellent penetration depth at low frequencies such as 0.915GHZ, or generally 0.9 to 2.5 GHz, where industrial/commercial microwave ovens operate. Therefore, microwave heating and sealing can offer unique advantages including selectively heating a thicker layer of seal materials. Since many of these sealing applications - especially vacuum insulated window sealing and solar cells encapsulation or OLED sealing applications - require a thicker seal material (over 20 microns), volumetric heating techniques such as microwave heating becomes a preferred method of sealing.

[0005] The invention relates to the use of microwave sealing of substrates to one another, including glass to glass seals, utilizing both tempered as well as annealed glass substrates.

[0006] An embodiment of the invention is a method of sealing two inorganic substrates together using a microwave energy source comprising: (a) providing first and second inorganic substrates; (b) applying to at least one of first and second substrates a paste composition including: (i) a glass frit, and (ii) a microwave coupling additive, and (c) subjecting the substrates and paste to microwave radiation, thereby forming a hermetic seal between the two inorganic substrates.

[0007] An embodiment of the invention is a lead-free and cadmium-free sealing glass composition, comprising, prior to firing, (a) 25-65 mol% Bi₂0₃, (b) 3-60 mol% ZnO, (c) 4-65 mol% B₂0₃, (d) 0.1-15 mol% of at least one selected from the group consisting of CuO, Fe₂0₃, Co₂0₃, Cr₂0₃, and combinations thereof, (e) no intentionally added oxides of silicon, and (f) no intentionally added oxides of aluminum.

[0008] An embodiment of the invention is a method of sealing a solar cell module comprising: (a) providing at least two glass plates, (b) positioning a plurality of solar cells in electrical contact with one another and in between these two glass plates, (c) applying any glass frit composition disclosed herein to at least one of the glass plates, (d) bringing at least a second glass plate into physical contact with the glass frit, and (e) subjecting the glass frit composition to microwave heating to sinter and flow the glass composition to thereby form a hermetic seal.

[0009] An embodiment of the invention is a method of sealing a vacuum insulated glass assembly comprising: (a) providing at least two glass plates (b) applying any glass frit composition disclosed herein to at least one of the glass plates, (b) bringing at least a second glass plate into contact with the applied glass frit composition and (d) subjecting the glass frit composition microwave heating to sinter and flow the glass composition to thereby form a hermetic seal. [0010] An embodiment of the invention is a method of sealing at least one electronic device such as an LED display or OLED display, or electronic circuit assemblies comprising: (a) providing at least two glass plates (b) applying any glass frit composition disclosed herein to at least one of the glass plates thereby forming a cavity, (c) placing the at least one electronic device into the cavity, (d) bringing at least a second glass plate into contact with the glass frit composition, and (e) subjecting the glass frit composition to microwave heating to sinter and flow the glass frit composition to thereby form a hermetic seal.

[0011] An embodiment of the invention is a method of sealing an assembly comprising: (a) providing at least two glass plates (b) applying any glass composition disclosed herein to at a first of the glass plates, (c) placing the assembly into a cavity formed by the at least first of the glass plates and the glass frit composition, (d) bringing at least a second glass plate into contact with the glass frit composition, and (e) subjecting the glass frit composition to microwave heating to sinter and flow the glass frit composition to thereby form a hermetic seal.

[0012] An embodiment of the invention is a method of sealing an assembly used in automotives comprising: (a) providing at least two glass plates (b) applying any glass frit composition disclosed herein to at least one of the glass plates, (b) bringing at least a second glass plate into physical contact with the glass frit composition, and (d) subjecting the glass frit composition to microwave heating to sinter and flow the glass composition to thereby form a hermetic seal.

[0013] An embodiment of the invention is a method of sealing an assembly in buildings, such as smart windows, comprising: (a) providing at least two glass plates (b) applying any glass composition disclosed herein to at least one of the glass plates, (b) bringing at least a second glass plate, into physical contact with the glass frit composition, and (d) subjecting the glass frit composition to microwave heating to sinter and flow the glass frit composition to thereby form a hermetic seal.

[0014] An embodiment of the invention is a method of bonding first and second glass panels to one another, so as to hermetically seal and isolate a cavity defined there between, the method comprising, (a) providing a first homogeneous powder glass sealing composition comprising: (i) 25-65 mol% Bi₂0₃, (ii) 3-60 mol% ZnO, (iii) 4-65 mol% B₂0₃, (iv) no intentionally added oxides of silicon, and (v) no intentionally added oxides of aluminum, (b) providing a second homogeneous powder glass sealing composition comprising: (i) 37-45 mol% Bi₂0₃, (ii) 30-40 mol% ZnO, (iii) 18-35 mol% B₂0₃, (iv) 0.1-15 mol% of at least one selected from the group consisting of CuO, Fe₂03, Co₂0₃, Cr₂0₃, (v) no intentionally added oxides of silicon, and (vi) no intentionally added oxides of aluminum (c) mixing the first and second powders form a homogeneous mixture, (d) applying the homogeneous mixture to at least one of the first and second glass plates, (e) positioning the first and second glass plates such that the first and second powders come into contact with both glass plates, (f) subjecting the glass plates and powders to microwave heating with an electromagnetic field having a frequency of 0.9 to 2.5 GHZ, to sinter and flow the first and second powders thereby forming a hermetic seal defining a cavity between the first and second plates.

[0015] An embodiment of the invention is a lead-free and cadmium-free sealing glass composition, comprising, prior to firing, (a) 5-65 mol% ZnO, (b) 10-65 mol% SiO?, (c) 5-55 mol% B₂0₃ + A1₂0₃, (d) 0.1-45 mol% of at least one selected from the group consisting of Li₂0, Na₂0, K₂0, Cs₂0, and combinations thereof, and/or (e) 0.1-20 mol% of at least one selected from the group consisting of MgO, CaO, BaO, SrO and combinations thereof, and/or (f) 0.1-40 mol% of at least one selected from the group consisting of Te0_2, T1₂0, V2O5, Ta₂0₅, Ge0₂ and combinations thereof.

[0016] Another embodiment of the invention is a lead-free and cadmium-free sealing glass composition, comprising, prior to firing, (a) 5-55 mol% Li₂0+Na₂0+K₂0, (b) 2-26 mol% Ti0₂, (c) 5-75 mol% B₂0₃ + Si0₂, (d) 0.1-30 mol% of at least one selected from the group consisting of V₂0₅, Sb₂0₅, P₂0₅, and combinations thereof, (e) 0.1-20 mol% of at least one selected from the group consisting of MgO, CaO, BaO, SrO, and combinations thereof, (f) 0.1-40 mol% of at least one selected from the group consisting of Te0₂, T1₂0, Ta₂0₅, Ge0₂ and combinations thereof, and (g) 0.1 -20 mol% F.

[0017] Still another embodiment of the invention is a method of sealing an assembly comprising: (a) providing at least two glass plates where in at least one glass plate is a smart glass (b) applying a glass frit composition to at least a first of the glass plates, (c) bringing at least a second glass plate into contact with the glass frit composition, and (d) subjecting the seal to microwave heating to sinter and flow the glass composition to thereby form a hermetic seal.

[0018] Suitable microwave coupling additives include ferrimagnetic metals, transition metals, iron, cobalt, nickel, gadolinium, dysprosium, MnBi alloy, MnSb alloy, MnAs alloy, CuO*Fe₂0₃, FeO, Fe₂0₃, Fe₃0₄ MgO»Fe₂0₃, Mn0«Fe₂0₃, NiO*Fe₂0₃, Y₃Fe₅0i₂, iron oxide containing glasses such as Fe₂03-glasses, SiC, Cr0₂, alkaline earth titanates, rhenium-titanates, rhenium- bismuth titanates, rare earth titanates, microwave dielectrics such as ULF800 (rhenium-titanate frit with density 4.37 g/cc that sinters at 900 °C); C0G620H (rhenium titanate with density of 5.65 g/cc that sinters at 1260 °C); C0G820MW (rhenium-bismuth-titanate with density of 5.68 g/cc that sinters at 1330 °C) from Ferro corporation, and combinations thereof.

[0019] Alternately, enamels can be prefired to each of top and bottom glass plates, and then a portion of microwave coupling containing enamel is applied to at least one of the enamel prefires. Then the top and bottom glass plates are sealed together by subjecting the seal through microwave heating. Prefiring eliminates the need to process a large mass of sealing material in a solar cell fabrication facility, and prevents excess heating of the photovoltaic device. For the final sealing fire, contamination from binder burnout is eliminated, as no organic binder is needed. In the aggregate, the sealing method carried out by the procedures outlined herein is faster than conventional methods, largely because the prefiring reduces the mass of frit that must be fired at the moment of seal formation

[0020] Although prefiring enamel layers before microwave sealing is beneficial to control bubbles, it is also envisioned, and in fact preferred, that direct sealing without prefiring is possible. Further, the enamel layers may be applied to only one of a pair of substrates to be sealed together. Similarly it is envisioned that sealing materials (enamel layers) can all be applied to the same plate (top or bottom) and selectively sealed to the other plate with or without prefiring the enamel. For the faster manufacturing it is preferred to have the enamels on the bottom plate and apply no enamel to the top plate to achieve maximum irradiated microwave energy to the enamels on the bottom plate where it is desired.

[0021] An embodiment of the invention is a multi-cell solar array comprising a plurality of individually hermetically sealed solar cells. In many of the practically useful applications of glass to glass sealing, such as encapsulation of solar cells (crystalline silicon as well as thin films based CdTe &CIGS, polymeric, flexible), OLED packaging, displays, and vacuum insulated windows sealing, and architectural & automotive windows sealing, there exists a need to use tempered glasses in many instances. Glasses lose temper when heated above about 300°C in conventional furnace firing of sealing glass materials. Therefore, there exists a need to selectively heat the seal material alone and to effect the bonding to the base glasses/substrates without significantly heating the base glasses/substrates. [0022] Envisioned herein is the use of products made by microwave heating and melting systems industry leaders such as Gyrotron Technology, Inc. 3412 Progress Drive, Bensalem, PA 19020 (www.gyrotrontech.com) which produces unique microwave heating technology, employing a high frequency concentrated microwave applicator to melt glasses. The Gyrotron Beam is a concentrated source of energy. Its high frequency and high energy concentration combined with the microwave nature of this novel source results in unique properties, different from any other known source of energy. The beam can perform the following functions: rapid volumetric heating of non-metallic materials from 10 microns to 30 cm (.0004" to 12"), meaning heating that is faster than heat conduction and oxidation methods; rapid selective heating, where a target region inside an exposed material can be heated differentially from surrounding regions. The Gyrotron Beam is an efficient heat source for the processing of any kind of polymer based materials, organics, ceramics, semiconductors, glass, wood, and other non-metallic materials.

[0023] The Gyrotron Beam is the first microwave source in the form of a beam. It has a heat flux of up to 15 kW / sq. cm, for example 1-15 kW/ sq. cm. It performs rapid heating at normal and low pressure: up to 10,000 °C /second, for example 0.1 to 10,000 °C/ second; provides selective and/or exclusive heating of target region or layer inside or on surfaces without significant heating of other layers. The beam can take any form, for example circular with diameter of 3mm (0.12") or more; a strip with length up to 2m (6 feet), square and ellipse up to 60 sq ft. The beam can also be split to support two production lines or heat two sides of a product being processed simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 depicts a simple microwave-heated fused seal between two glass plates.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Broadly in selective sealing methods localized heating occurs due either to preferential absorption of electromagnetic waves of interest due to the presence of suitable absorbers, or couplers in the seal materials. This leads to selective heating of seals. Control of various aspects of this selective sealing method such as: amount and location of absorption and heat generation; controlling heat dissipation to minimize the occurrence of thermal gradients or thermal shock— through materials and seal designs, especially for one such selective sealing method— Microwave Sealing— are other aspects of the invention.

[0026] The invention involves controlling the amount of microwave energy deposition, the location of the deposition of this energy, and the rate of deposition of this energy, so that a high quality seal is formed, eliminating fractures due to thermal shock and thermal expansion mismatches that would compromise the hermeticity of the seal are prevented or minimized.

[0027] The method for forming hermetic seals according to this invention is simple in concept, but quite difficult to achieve in practice. Note that the formation of a hermetic seal requires near perfection since even a single gap or leak in a large solar module or VIG panel, which may be on 0.8m x 1.2 m to 2m x 3m glass substrates, compromises the seal and lifetime of the solar module or loss of insulating power of VIG unit. The sealing glass or enamel can either be preglazed (or prefired) on the glass plates before microwave sealing the glass plates together, or directly sealed without preglazing. It should be appreciated that bubbles present in an enamel or that may form during the sealing operation will expand in size during the heating, forming larger voids that could compromise the integrity of the seal. Therefore depending on the seal geometry and glass plates sizes the enamel layer can either be preglazed or not.

[0028] In principle, this invention entails minimizing any dimensional changes, depositing the majority of the energy at the site of the interface to be sealed, controlling and minimizing average bubble sizes and then minimizing any thermal gradients and expansion mismatches to minimize the chance for fractures from thermal shock or thermal expansion mismatch.

[0029] The dimensional changes are primarily eliminated by the use of fired (preglazed) enamels that have been densified/sintered from dried depositions having bulk densities of about 60% or less of their theoretical density, to fired enamels with at least 90% of theoretical density. However, it should also be recognized that bonding a substrate having a preglazed enamel to one with a thin layer of dried enamel paste would give only minor dimensional changes and would work nearly as well, and is also part of this invention. Another purpose of the preglazed fired enamels on substrates is to create high-quality enamel-substrate interfaces.

[0030] Another embodiment of the invention concerns controlling the location of energy deposition. In microwave sealing electromagnetic fields of high intensity are created by microwave generators such as those from Gyrotron Technology, Inc. In fact the Gyrotron beam is the first microwave source in the form of a beam. This beam can provide rapid volumetric heating of various substrate materials - polymers, organics, ceramics, semiconductors, glass, wood, and other non-metallic materials. It has a heat flux of up to 15kW per sq, cm. The heating rate of at least a portion of the substrates and paste may be 0.1 to 10,000 °C per second. The beam may take any of the following shapes: circular, square, elliptical, or split.

[0031] The glass by itself can be heated by microwaves. However, additions of microwave coupling additives will increase the microwave absorption of the seal materials. Suitable microwave coupling additives include ferrimagnetic metals, transition metals, iron, cobalt, nickel, gadolinium, dysprosium, MnBi alloy, MnSb alloy, MnAs alloy, CuO*Fe₂0₃, FeO, Fe₂0₃, Fe₃0₄ MgO»Fe₂0₃, MnO*Fe₂0₃, NiO*Fe₂0₃ Y₃Fe₅0]₂, iron oxide containing glasses preferably Fe₂0₃-glasses, SiC, Cr0₂, alkaline earth titanates, rhenium-titanates, rhenium-bismuth titanates, rare earth titanates, microwave dielectrics such as ULF800; C0G620H; C0G820MW from Ferro corporation, and combinations thereof.

[0032] Still another embodiment of the invention relates to shape and size of these coupling agents. To effect volumetric heating in seal glass material, addition of coupling materials which are particulates having shapes selected from the group consisting of high sphericity, low sphericity, irregular, equant, ellipsoidal, tabular, cylindrical, flake, whisker and wire geometries, is envisioned, to generate the heat throughout the seal. The D₅₀ particle size can be in the range of 5 nm to 100,000 nm, preferably 10 nm to 50,000 ran, more preferably 50 nm to 10,000 nm.

[0033] Yet another embodiment of the invention relates to preventing stresses that would weaken the seal and preventing fractures that would compromise the hermeticity of the seal. This is done by controlling the composition of the enamel and the parameters of the sealing technique. Although it is not a requirement for the use of this invention, the use of preglazed enamels is extremely helpful for forming high-quality hermetic seals. The use of dried enamels for the sealing step results in significant dimensional changes when the coating has a substantial thickness, making formation of the seal more difficult. In addition, the dried enamels are prone to form large voids in the seal, and also tend to blow some contamination to the inside of the cell module or VIG panel during the sealing method.

[0034] Another embodiment of this invention is addition of the aforementioned coupling materials to low temperature seal glass materials disclosed in commonly owned copending PCT/US2011/032689 (U.S. Ser. No. 13/641 ,046), incorporated by reference. The

aforementioned coupling materials may be added to commercial available materials such as EG2824, EG2824B and EG2824G from Ferro Corporation, Cleveland, OH. The seal glass materials stated here, are not limited to high bismuth glasses alone. We envision incorporation of some of these coupling materials to different seal glass systems, namely high lead glass seal materials based on low melting lead glasses such as EG2760; zinc glass systems such as CF7574, LF256; bismuth zinc borate glasses such as EG2871 ; high barium glasses; high calcium glasses; alkali silicate glasses containing titanium and/or zinc such as EG3600, EG3608. The above named glasses are commercially available from Ferro Corporation, Cleveland Ohio and are broadly disclosed in the following tables.

[0035] Table 1. Broad ranges for individual oxides to be used in sealing glass frits. The glass frits broadly have softening points of 250 to 800 °C.

[0036] Table 2. Ranges for individual additional oxides to be used in sealing glass frits in minor amounts.

CuO 0-15 0.1-10 2-9.5 3-9 5-8.5 6-8.5

Co₂0₃ 0-15 0.1-10 2-9.75 4-9.5 6-9 7.5-9

MnO 0-15 0.1-10 1.5-9 2-8 4-7 4-7

NiO 0-15 0.1-10 1.5-9 2-8 4-7 4-7

(Ta₂0₅+P₂0₅ 0-10 0-8 0-6 0.1 -5 0.1-4 0.1-4

W0₃+Mo0₃+SnO)

(Te0₂+Tl20+V₂0₅+Ge02) 0-40 0-30 0-20 0.1-30 0-10 0.1-15

F₂ 0-15 0-10 0-8 1-6 2-6 2-6

[0037] Alternative ranges for individual additional oxides in Table 2 include, for CuO, Fe₂0₃, Co₂0₃, and MnO, in mol%: 1.5-9, 2-8 and 4-7. Alternate ranges for La₂0₃ include 0.5-8, 2-6 and 1-6 mol%.

[0038] Oxides in Tables 2 or 4, including the alternatives in the preceding paragraph, can be used in any amount disclosed in any column together with oxides from Table 1 or 3. Amounts from different columns in Tables 2 or 4 can be used with amounts of oxides from any column in Table 1 or 3.

[0039] It is to be noted that part of these glass oxides such as Bi₂0₃, ZnO, CuO, Fe₂0₃, Co₂0₃, MnO, can be included as ceramic oxide additives in the seal materials to obtain the final overall glass compositions envisioned here.

[0040] As mentioned previously multiple glasses, preferably glass mixtures of two or three frits can be used to control the overall properties of the seal. If a second glass composition is used, the proportions of the glass compositions can be varied to control the extent of paste interaction with substrates such as silicon, flow and crystallization characteristics of the seal and hence the resultant seal properties. For example, within the glass component, the first and second glass compositions may be present in a weight ratio of about 1 :20 to about 20: 1 , and preferably about 1 :5 to about 5:1. The glass component preferably contains no lead or oxides of lead, and no cadmium or oxides of cadmium. However, in certain embodiments where the properties of PbO cannot be duplicated, such embodiments advantageously comprise PbO.

Further the second or third glass can be another bismuth glass from Tables 1 & 2, or a zinc glass (Table 3) or alkali titanium silicate glass (Table 4) or a lead glass (Table 5 or 6). [0041] Table 3. Oxide frit ingredients for zinc based additive glasses in mole percent.

[0042] Table 4. Oxide frit ingredients for alkali-titanium-silicate additive glasses in mole percent.

[0043] Table 5. Oxide frit ingredients for lead based additive glasses in mole percent.

(Li₂0 + Na₂0 + K₂0+Cs₂0) 0-40 0-30 0-10

Ti0₂+Zr0₂ 0-20 0-10 0.1-5

(MgO + CaO + BaO + SrO) 0-20 0-15 0-10

(Te0₂+Tl₂0+V₂0₅+Ta₂0₅+Ge0₂) 0-40 0-30 0-15

F₂ 0-15 0-10 0-8

Table 6. Oxide frit ingredients for lead vanadium based additive glasses in mole

10045] Sealing glass compositions of the invention can be lead-free and cadmium free, in one embodiment, the lead-free and cadmium-free sealing glass composition, comprise, prior to firing, (a) 25-65 mol% Bi₂0₃, (b) 3-60 mol% ZnO (c) 4-65 mol% B₂0₃, (d) 0.1-15 mol% of at least one selected from the group consisting of CuO, Fe₂0₃, Co₂0₃, Cr₂0₃, and combinations thereof, (e) no intentionally added oxides of silicon, and (f) no intentionally added oxides of aluminum.

[0046] In addition to other embodiments, the glasses used in the invention may be selected from the group consisting of bismuth glass, lead glass, zinc glass, barium glass, calcium glass, alkali silicate glasses, vanadium glass, telluride glass, phosphate glass and combinations thereof.

[0047] Yet another embodiment of this invention is adding these coupling materials to epoxies as well organic-inorganic hybrid materials to effect the heating, flowing and bonding of substrates glass to glass, glass to metal, and glass to ceramic sealing.

[0048] Yet another embodiment of this invention is at least one of the glass plate is tempered. [0049] Yet another embodiment of this invention is at least one of the glass plate is a pre laminated glass assembly.

[0050] Yet another embodiment of this invention is at least one of the glass plate is coated with conductive coatings such as tin oxide (TCO) or indium-tin oxide (ITO) material.

[0051] Yet another embodiment of this invention is other enamels or pastes are fired along with the sealing glass or enamel layers of this invention.

[0052] Yet another embodiment of this invention is an exact feed through is incorporated on glass plates and is either sealed together with, or separately from, seal enamel firing.

[0053] Broadly, a process of induction sealing begins with prefiring an induction coupling containing enamel composition on a top glass plate. Then the top plate is placed over the bottom plate. Then a microwave heating source is targeted to the assembly, to melt the top surface of the energy absorbing/coupling enamel and bond the pieces together.

[0054] Alternately, microwave coupling containing enamels are prefired to each of top and bottom glass plates. Then the plates are placed together and subject to heating by a microwave source to complete the seal.

[0055] Prefiring eliminates the need to process a large mass of sealing material in a solar cell fabrication facility, and prevents excess heating of the photovoltaic device. For the final sealing fire, contamination from binder burnout is eliminated, as no organic binder is needed. In the aggregate, the sealing method carried out by the procedures outlined herein is faster than conventional methods, largely because the prefiring reduces the mass of frit that must be fired at the moment of seal formation.

[0056] Although prefired enamel layers before microwave sealing is preferred, it is also envisioned that direct sealing without prefiring is possible.

[0057] Similarly it is envisioned that sealing materials (enamel layers) can all be applied to the same plate (top or bottom) and selectively sealed to the other plate with or without prefiring the enamel.

[0058] Various embodiments of the invention may involve various procedures for application of microwave coupling enamel layers. The application procedures may include one or more of screen printing, paste extrusion, ink jet printing, digital application procedures using ink jet or spray deposition, automatic syringe dispensing such as by the use of Nordson robotic dispenser systems, spin coating, dip coating and others. [0059] Another embodiment of the invention is a sealant material system for use in joining two or more inorganic substrates that are used to form a photovoltaic device, said sealant material system comprising one or more glass or ceramic components. The sealant material system may include any glass and/or metal and/or oxide in any combination, disclosed herein.

[0060] In any embodiment herein, a vacuum or inert atmosphere may be sealed in a space created by the at least two inorganic substrates together with the sealant material system.

[0061] An embodiment of the invention is a sealant material system for use in joining two or more inorganic substrates contained in a photovoltaic device upon application of a concentrated energy source. The sealant material system may include any glass and/or oxide in any combination, disclosed herein.

[0062] An embodiment of the invention is a multi-cell solar array comprising a plurality of individually hermetically sealed solar cells. In many of the practically useful applications of glass to glass sealing, such as encapsulation of solar cells (crystalline silicon as well as thin films based CdTe &CIGS, polymeric, flexible), OLED packaging, displays, and vacuum insulated windows sealing, and architectural & automotive windows sealing, there exists a need to use tempered glasses in many instances. Soda-lime silica glass substrates lose their temper when heated above about 300°C in conventional furnace firing of sealing glass materials. Therefore, there exists a need to selectively heat the seal material alone and to effect the bonding to the base glasses/substrates without significantly heating the base glasses/substrates.

[0063] Envisioned herein is the use of products made by microwave heating and melting systems industry leaders such as Gyrotron Technology, Inc. 3412 Progress Drive, Bensalem, PA 19020 (www.gyrotrontech.com) as they have unique microwave heating technology, which employs

[0064] The present invention contemplates three different designs as shown in Figures 1 to 3, for induction sealing of glass plates. In Figure 1 it is a simple seal between two glass plates. In Figure 2 the seal has a metallic interlayer. In Figure 3 the outer metal piece is inductively heated to effect glass to metal seals.

[0065] In particular, Figure 1 depicts an embodiment with glass plates 110 and 120 joined by a green inductive sealing glass 130 (seal glass and induction coupling additive) to form assembly 100. Assembly 100 is subjected to heating which fuses the glass in seal 130 to a solid hermetic seal. Cavity 140 may house an active layer (not shown) or a special atmosphere, such as an inert atmosphere, such as N₂, He, Ar, or a partial vacuum, to a pressure of 500 torr, 400 torr, 300 torr, 200 torr, or even 100 torr, to the hermeticity limit of the sealant material used to seal the glass plates 110 and 120 together.

[0066] All ranges herein are presumed to include "about" referring to both the upper and lower limits of such ranges. An entry such as 1-10 % Te0₂+Ta₂Q5+ T1₂0 +Ge0₂ means that any or all of the named oxides may be present up to a total of 1-10% of the composition.

[0067] Details about aspects of the invention can be found in one or more of the following United States Patent Applications, all of which are commonly owned, and all of which are incorporated herein by reference: 10/864,304; 10/988,208; 1 1/131 ,919; 1 1/145,538; 1 1/384,838; 1 1/774,632; 1 1/846,552; 12/097,823; 12/298,956; 12/573,209; 61/324,356; 61/328,258;

61/366,568; and 61/366,578.

Claims

1. A method of sealing two inorganic substrates together using a microwave energy source comprising:

a. providing first and second inorganic substrates;

b. applying to at least one of first and second substrates a paste composition including: i. a glass frit, and

ii. a microwave coupling additive,

c. arranging the substrates such that the paste composition lies therebetween and in contact with both substrates, and

d. subjecting the substrates and paste to microwave radiation, thereby forming a

hermetic seal between the two inorganic substrates.

2. The method of claim 1 , wherein the microwave radiation has a frequency of about 0.9 GHz to about 2.5 GHz.

3. The method of claim 1 , wherein the microwave radiation has a frequency of about 0.915 GHz.

4. The method of claim 1 , wherein the microwave radiation provides a heat flux of 0.1 to 15 kW per square centimeter.

5. The method of claim 1, wherein the microwave radiation heats at least a portion of the

substrates and paste at a rate of 0.1 to 10,000 °C per second.

6. The method of claim 1, wherein the microwave radiation is provided in the form of a circular beam having a diameter of 3 millimeters to 10 centimeters.

7. The method of claim 1 , wherein the microwave radiation is provided in the form of a beam having a cross section selected from the group consisting of circular, square, elliptical or split.

8. The method of claim 1 , wherein one of the substrates is glass and the other substrate is ceramic.

9. The method of claim 1, wherein the glass frit is selected from the group consisting of

EG2824, EG2824B, EG2824G, EG2760, S46/6; LF256, GL4317, BBS2, EG0026, and combinations thereof.

10. The method of claim 9, wherein the paste further comprises Ti0₂.

1 1. The method of claim 1 , wherein the microwave coupling additive is selected from the group consisting of ferromagnetic metals, transition metals, iron, cobalt, nickel, gadolinium, dysprosium, MnBi alloy, MnSb alloy, MnAs alloy, CuO*Fe₂0₃, FeO, Fe₂0₃, Fe₃0₄

MgO*Fe₂0₃, MnO*Fe₂0₃, NiO«Fe₂0₃, Y₃Fe₅0i₂, iron oxide containing glasses, Fe₂0₃- glasses, SiC, Cr0₂, alkaline earth titanates, rhenium-titanates, rhenium-bismuth titanates, rare earth titanates, and combinations thereof.

12. The method of claim 1 , wherein the microwave coupling additive is selected from the group consisting of rhenium titanate, rhenium bismuth titanates, and combinations thereof.

13. The method of claim 1, wherein the paste further comprises a manganese-containing

constituent selected from the group consisting of bismuth manganese pigments, perovskite manganites, Βϊ₂Μπ4θιο, Bi^MnCho and a bismuth-manganese pigment having a mole ratio of Bi₂0₃ to Mn0₂ of 5: 1 to 1 :5.

14. The method of claim 1 , wherein the paste further comprises a Mn(II) additive.

15. The method of claim 14, wherein the Mn(II) additive is selected from the group consisting of MnO, MnO-containing glasses, Mn(II) pigments, perovskite manganites, and combinations thereof.

16. The method of claim 1 , wherein magnetic metallic glass wires are interspersed in the paste.

17. The method of claim 1 , wherein the paste further comprises a microwave susceptor material.

18. The method of claim 17, wherein the microwave susceptor material comprises SiC.

19. The method of claim 1 , wherein the paste further comprises at least one selected from the group consisting of an epoxy and an organic-inorganic hybrid material, and wherein, with the proviso that the first substrate is glass, the second substrate is selected from the group consisting of glass, metal, and ceramic.

20. The method of claim 1 , wherein the glass frit comprises prior to firing :

a. 25-65 mol% Bi₂0₃,

b. 3-60 mol% ZnO,

c. 4-65 mol% B₂0₃,

d. 0.1 -15 mol% of at least one selected from the group consisting of CuO, Fe₂0₃, C02O3, Cr₂0₃, and combinations thereof,

e. no intentionally added oxides of silicon, and

f. no intentionally added oxides of aluminum.

21. A lead-free and cadmium-free sealing glass composition, comprising, prior to firing, (a) 25- 65 mol% Bi₂0₃, (b) 3-60 mol% ZnO, (c) 4-65 mol% B₂0₃, (d) 0.1-15 mol% of at least one selected from the group consisting of CuO, Fe₂0₃, Co₂0₃, Cr₂0₃, and combinations thereof, (e) no intentionally added oxides of silicon, and (f) no intentionally added oxides of aluminum.

22. A method of forming a hermetically sealed cavity comprising:

a. providing at least two glass plates,

b. applying a glass composition selected from the group consisting of glass 1 , glass 2 and glass 3, to at least one of the glass plates, wherein glass 1 , glass 2, and glass 3 comprise, respectively, i. glass 1 :

1. 25-65 mol% Bi₂0₃,

2. 3-60 mol% ZnO,

3. 4-65 mol% B₂0₃,

4. 0.1 -15 mol% of at least one selected from the group consisting of CuO, Fe₂0₃, Co₂0₃, Cr₂0₃, and combinations thereof,

5. no intentionally added oxides of silicon, and

6. no intentionally added oxides of aluminum,

ii. glass 2:

1. 37-45 mol% Bi₂0₃,

2. 30-40 mol% ZnO,

3. 18-35 mol% B₂0₃,

4. 0.1 -15 mol% of at least one selected from the group consisting of CuO, Fe₂0₃, Co₂0₃, Cr₂0₃,

5. no intentionally added oxides of silicon, and

6. no intentionally added oxides of aluminum

iii. glass 3:

1. 5-65 mol% ZnO,

2. 10-65 mol% Si0₂,

3. 5-55 mol% B₂0₃ + A1₂0₃,

a. and at least one selected from the group consisting of:

i. 0.1 -45 mol% of at least one selected from the group consisting of Li₂0, Na₂0, K₂0, Cs₂0, and combinations thereof,

ii. 0.1 -20 mol% of at least one selected from the group consisting of MgO, CaO, BaO, SrO and combinations thereof, and

iii. 0.1 -40 mol% of at least one selected from the group consisting of Te0_2i T1₂0, V₂0₅, Ta₂0₅, Ge0₂, c. bringing at least a second glass plate into contact with the glass composition into physical contact with one another, and d. subjecting the glass composition to microwave heating to sinter and flow the glass composition to thereby form a hermetic seal.

23. A method of bonding first and second glass plates to one another, so as to hermetically seal and isolate a cavity defined there between, the method comprising,

a. providing a first homogeneous powder glass sealing composition comprising:

i. 25-65 mol% Bi₂0₃,

ii. 3-60 mol% ZnO,

iii. 4-65 mol% B₂0₃,

iv. no intentionally added oxides of silicon, and

v. no intentionally added oxides of aluminum,

b. providing a second homogeneous powder glass sealing composition comprising: i. 37-45 mol% Bi₂0₃,

ii. 30-40 mol% ZnO,

iii. 18-35 mol% B₂0₃,

iv. 0.1-15 mol% of at least one selected from the group consisting of CuO, Fe₂0₃, Co₂0₃, Cr₂0₃,

v. no intentionally added oxides of silicon, and

vi. no intentionally added oxides of aluminum,

c. mixing the first and second powders form a homogeneous mixture,

d. applying the homogeneous mixture to at least one of the first and second glass plates, e. positioning the first and second glass plates such that the first and second powders come into contact with both glass plates, and

f. subjecting the glass plates and powders to microwave heating with an

electromagnetic field having a frequency of 0.9 to 2.5 GHZ, to sinter and flow the first and second powders thereby forming a hermetic seal defining a cavity between the first and second plates.

24. The method of claim 23, wherein at least one glass panel is a smart glass panel.

25. A lead-free and cadmium-free sealing glass composition, comprising, prior to firing, a. 5-65 mol% ZnO,

b. 10-65 mol% Si0₂,

c. 5-55 mol% B₂0₃ + A1₂0₃,

d. at least one selected from the group consisting of i, ii, iii:

i. 0.1-45 mol% of at least one selected from the group consisting of Li₂0, Na₂0, K₂0, Cs₂0, and combinations thereof,

ii. 0.1-20 mol% of at least one selected from the group consisting of MgO, CaO, BaO, SrO and combinations thereof, and

iii. 0.1-40 mol% of at least one selected from the group consisting of Te0₂, T1₂0, V2O5, Ta₂0₅, Ge0₂ and combinations thereof.

26. A lead-free and cadmium-free sealing glass composition, comprising, prior to firing,

a. 5-55 mol% Li₂0+Na₂0+K₂0,

b. 2-26 mol% Ti0₂,

c. 5-75 mol% B₂0₃ + Si0₂,

d. 0.1-30 mol% of at least one selected from the group consisting of V₂0₅, Sb₂0₅, P₂0₅, and combinations thereof,

e. 0.1-20 mol% of at least one selected from the group consisting of MgO, CaO, BaO, SrO, and combinations thereof,

f. 0.1-40 mol% of at least one selected from the group consisting of Te0₂, T1₂0, Ta₂0₅, Ge0₂ and combinations thereof, and

g. 0.1-20 mol% F.

27. The method of claim 1 , wherein the glass frit composition is selected from the group consisting of glass 1, glass 2 and glass 3, wherein glass 1 , glass 2, and glass 3 comprise, respectively,

a. glass 1 :

i. 25-65 mol% Bi₂0₃,

ii. 3-60 mol% ZnO,

iii. 4-65 mol% B₂0₃,

iv. 0.1-15 mol% of at least one selected from the group consisting of CuO, Fe₂0₃, Co₂0₃, Cr₂0₃, and combinations thereof,

v. no intentionally added oxides of silicon, and

vi. no intentionally added oxides of aluminum,

b. glass 2:

i. 37-45 mol% Bi₂0₃,

ii. 30-40 mol% ZnO,

iii. 18-35 mol% B₂0₃,

v. no intentionally added oxides of silicon, and

vi. no intentionally added oxides of aluminum, and

c. glass 3:

i. 5-65 mol% ZnO,

ii. 10-65 mol% Si0₂,

iii. 5-55 mol% B₂0₃ + A1₂0₃,

1. and at least one selected from the group consisting of:

a. 0.1-45 mol% of at least one selected from the group consisting of Li₂0, Na₂0, K₂0, Cs₂0, and combinations thereof, b. 0.1-20 mol% of at least one selected from the group consisting of MgO, CaO, BaO, SrO and combinations thereof, and c. 0.1 -40 mol% of at least one selected from the group consisting of Te0_2, Tl₂0, V₂0₅, Ta₂0₅, Ge0₂.