Transparent Ultra-Barrier Film Production and Product Integration

Transcription

1 Transparent Ultra-Barrier Film Production and Product Integration Mark George, Martin Rosenblum, Jason Bloking Rex Chang Vitriflex Inc., 2350 Zanker Road, Suite 20, San Jose, CA Introduction Vitriflex has developed a R2R deposition equipment and process to produce highperformance transparent ultra-barrier flexible plastic films at production yields. These plastic films are used as indirect encapsulation of flexible opto-electronics such as photovoltaic thin film solar cells, OLED displays and lighting, quantum dot and electrophoretic displays. These plastic barrier films are laminated to encapsulation these devices. The integration of these films requires adhesion to other optical films while maintaining total light transmittance and for display applications, control of color. Barrier Adhesion The R2R coater is equipped with a remote plasma source that is used to provide plasma treatment of the front surface of the plastic film prior to barrier deposition. The properlay applied plasma treatment not only improves film adhesion but also the water vapor transport rate (WVTR). We have qualified several different plastic films that are suitable for ultra-barrier performance. Figure 1 shows a typical evaluation of plasma treatment efficacy for WVTR at different plasma pretreat doses. Figure 1. WVTR vs Plasma Pretreat Dose Figure 1. Example of WVTR as a function of plasma pretreat dose.

2 The remote plasma source is a Sputtering Components Incorporated envis-ion DMPTS operated with a PEII Advanced Energy 40 khz power supply operated at 5 millitorr in 50% Argon/Oxygen mixture. Barrier Film Lamination: Solar Module Example The barrier films are not used free standing, but are laminated in a stack to encapsulate the optoelectronic device. This is illustrated in Figure 2 for a thin film solar module. Figure 3 shows the specific layers in our barrier film and the interfaces facing the encapsulants. The PET film supports the barrier stack and is supplied with an organic primer that must be selected for adhesion to the encapsulating adhesive. Figure 2 Encapsulated Thin Film Solar Device Figure 3 Encapsulation layers used for barrier film integration. There are three common types of laminating adhesives for thin film solar modules. These encapsulants come in three types of materials: ethyl vinyl acetate (EVA), thermal plastic polyolefin (TPO) and polyolefin elastomer (POE). Each supplier of PET films offers several different primer options and encapsulant manufacturers offer unique formulations for each materials. This makes selection of a primer and encapsulant that have acceptable adhesion an iterative process with the solar module manufacturer. In Figure 4 we show T-peel adhesion results for a U (urethane) primer from two different suppliers and the same EVA formulation. The adhesion is measured initially after lamination and then once a week for 6 weeks. The lamination is exposed to an environment of 85 C/85% RH. Figure 4 T-peel results for two different suppliers (supplier 2 left and supplier 4 right) U primer and EVA Condition B. hi il S l i

3 The T-peel is performed on 10 mm wide strips. In this example adhesion of EVA condition B to supplier 2 s U primer decreases with duration of the environmental exposure. In contrast supplier 4 s U primer adhesion to EVA condition B improves with exposure. Even to the point that the PET undergoes cohesive failure (fracture). This lamination evaluation has to be performed on a case by case basis for each customer. In some cases our customers perform these tests on their own and in others it is a collaborative effort between the customer, substrate supplier, adhesive supplier and Vitriflex. In table I we show a summary of adhesion trials between three different EVA formulations and primers offered by these two PET suppliers. TABLE I. Adhesion results for PET surface primers and EVA Adhesion >30N/cm passes the T-peel test after C/85%RH The limited options for acceptable primers on the PET, places a constraint on the available PET film manufacturing. Minimum order quantities for PET with specific front surface and back surface primers usually range from 5 to 20 metric tons, depending on the manufacturer. These MOQ s are often much larger than customer s barrier film order. This places a significant burden for cash flow, inventory storage and scheduling. These factors therefore require a customer commitment for orders between 50,000 to 250,000 m 2 depending on PET thickness and MOQ for a specific supplier. Barrier Stack Color Control Display applications are very sensitive to color of the emitted light that propagates through the layers in the laminated device. Our ultra-barrier films are composed of two different films of inorganic mixed metal oxides. One film is a highly amorphous thin film (A layer) that acts as a diffusive barrier to oxygen and water and the second film is polycrystalline (C layer) material with a gettering function designed to coordinate water or oxygen within its matrix.

4 The A layer has an index of refraction >2.10 and the C layer and index <1.5. Therefore control of their layer thicknesses can create an index match to the laminating material. A TEM cross-section of the three layer barrier stack is shown in Figure 5. For specific customer device integration the thicknesses of the three layers are optimized to control the color of the light emitted from the device. The specific layers involved for a typical device application are shown in figure 6. Figure 5. TEM image of 3 layers of Figure 6. Stack architecture for emissive display device The color of the light must be maintained through the entire stack. In order to adjust the color emitted from the device the only adjustable layer thicknesses are the A and C layers of the barrier stack. For this particular device application the CIE Lab color coordinate requirements for the transmitted light is a*<±1.5, b*<±1.75 and L>93. The A layer thickness next to the planarization has a constraint of a minimum thickness in order to ensure the proper barrier performance. We employed OptiLayer multilayer optical thin film modeling program in the stacks modeling module to optimize the A/C/A layer thicknesses with the first A layer minimum thickness constraint and thickness variation of +/-7% of the primer and planarization layers. We came up with two designs that met these constraints and allow the R2R coater to operate at line speeds of approximately 2 m/min meeting coater throughput required to meet the market cost for barrier film. Figure 7. Stack optical transmission for barrier design 1. Figure 8. Stack optical transmission for barrier design 2.

5 Figures 7 and 8 show the transmittance of a laminated stack with these two barrier layer designs. Spectra were acquired at 5 different cross web locations. The non-laminted PET transmittance spectra are also included for reference. One can immediately observe that design 1 only meets the color requirements once the barrier is laminated to the other layers. Both of these designs can achieve the color coordinates with small changes of solution coating thickness variation cross-web and still meet a WVTR <5e-04 grams/m2/day at 40 C and 100% RH as shown in Figures ( 9& 10; respectively). Figure 9. CIE Lab space results for Designs 1 and Designs 2. Figure 10. WVTR for Design 1 measured by MOCON on an AQ1. Below detection limit of AQ1. Independent measurement of the WVTR by the calcium reaction test method was provided by one of our customers. Figure 11 shows the calcium test setup. 10 nm of calcium was deposited on the barrier surface and encapsulated in aluminum. The increase in reflection was used as a measure of calcium conversion as a function of exposure time at 40 C and 90%RH. These data show that barrier films had WVTR below 1E-5 grams/m 2 40 C & 90%RH.

6 Figure 11. WVTR performance of 3 layer barrier by calcium method. R2R Deposition System and Manufacturing Yield The roll-to-roll barrier coater utilizes six independently controlled sputter deposition zones. The sputtering process is controlled by a proprietary feedback control scheme that keeps the targets from being operated in the poisoned state. To keep the optical performance the sputter deposition rates must be controlled with a deviation less than 1.5% down web and cross-web over the duration of a production run. The R2R coater is shown in Figure 12. Figure 12. AEGIs R2R sputter coater. Six sputter deposition zones with a maximum coated width of1300 mm. Production runs can have durations up to 18 hours per roll depending on line speed and roll length. We have run several production campaigns of our 3-Layer barrier coating up to 25 consecutive rolls. During the latest 25 roll campaign of 1100 meter rolls, we had an average yield of >91%. The turn around time (pump, coat, vent) for individual rolls was 12 hours. The roll yield losses include 31 meters for IQC, OQC, startup material threading, rewind and trimming. During this particular campaign we increased the line speed by a factor of 2 over our previous process of record by increasing the power to the sputtering magnetrons. As a result of this increase we damaged some of the sputter power supplies and their output cables by running the sputter power supplies at 100% of their rated power. The SCAD system is setup to automatically stop the coating run upon system faults. Upon startup after the SCADA system automatically shut down the system, wrinkles developed upon restart. The development of the wrinkles was avoided in future rolls due to implementation of a new startup procedure after a run fault. Figure 13 shows the average yield and individual roll yields for this campaign. The rolls that experienced startup wrinkles include rolls 17,18 and 19. Other failure modes we experienced during this campaign include: air compressor failure

7 and post-coating edge trimming failure. All rolls met the minimum transmittance (>90%) and had a WVTR <5e-3 grams/m 2 /day, below the detection limit of the MOCON W-700. Figure 13. Production campaign of 25 consecutive rolls. Overall average yield was >91%. Successful Integration PMOLED Example We have worked in a collaborative manner with Sinovia to support development of a flexible/rollable PMOLED device. Sinovia integrated their flexible silver nanotechnology into a top coat applied to our barrier film. This silver layer forms the anode in the PMOLED device and acts as the interface to the OLED layers. A second barrier film encapsulates the backside of this device. Figure 14. Example of Sinovia PMOLED flexible and foldable display. The device stack is shown on the right.

8 Conclusion The R2R production of 3 layer barrier coating with high yield has been demonstrated by our sputter roll to roll coater. However, before a customer can utilize our barrier films integration hurdles must be overcome making sure that the barrier films pass both inter film adhesion, optical and environmental testing when laminated into the customers product. Substrate primer coatings must be tailored to the customer s needs and meet the demanding requirements required for ultra-barrier performance. A successful collaboration to work out the integration hurdles has been demonstrated in a functional PMOLED device.