Patent Application
20250066597
The present invention relates to printed electronics such as polymer capacitors, capacitive sensors and dielectric for transistors, particularly those containing multi-layered dielectrics.
As the manufacturing cost of electronic devices decreases, the potential for emerging applications increases, such as the use of smart packaging. Some examples of these applications include the incorporation of electronic sensors within product packaging, such as radio-frequency identification (RFID) tags that enable consumers to access supplemental product information or temperature sensors to alert distributors and consumers that a product has been exposed to unsafe temperatures.
Smart packaging has quickly become a multi-billion-dollar industry, with the potential to dramatically reduce food waste and improve consumer experience and confidence. However, for smart packaging to be viable, the electronically active materials need to be environmentally friendly to reduce the footprint of the waste created, inexpensive, amenable to low-cost printing processes, and suitable for a variety of implementations. Additionally, the electronically active materials should provide a high dielectric constant (high-k), low leakage current, and no hysteresis.
Organic thin film transistors (OTFTs) and capacitors offer potential sources for smart packaging. OTFTs and capacitors are capable of detecting and signaling changes to a variety of conditions. OTFTs and capacitors are generally comprised of multiple layers (having various thicknesses), including electrodes, a semiconductor, and a dielectric. The dielectric can be classified into two main categories: organic or inorganic.
Organic (carbon based) dielectrics, or polymer dielectrics, have the potential to yield flexible and biodegradable devices through low-temperature and solution processing techniques, however these dielectrics typically suffer from higher leakage currents, a larger number of defects, and lower capacitances. These restrictions limit their ability to be utilized in a variety of applications, and decrease their overall performance.
Inorganic dielectrics, meanwhile, have lower leakage currents with well characterized performance metrics, but these materials require higher processing temperatures, higher operating voltages, and are not amenable to printing processes or many flexible applications.
Existing organic dielectrics used in OTFTs are not suitable for use in smart packaging. For example, poly (methyl methacrylate), poly (vinyl phenol), and poly (styrene) are undesirable for smart packaging as they are non-biodegradable. These OTFTs are further unsuitable for use in smart packaging due to low-k and low capacitance densities. Meanwhile organic dielectrics such as poly (vinyl alcohol) (PVA), a relatively high-k dielectric that is water soluble and environmentally friendly, is moisture sensitive and suffers from large leakage currents, poor film forming capabilities, and large hysteresis.
These limitations prevent wide-spread applicability of OTFTs and capacitors, due to
the expense and limitations in manufacturing, or the negative impact on the environment from introducing further non-biodegradable products into the product chain.
As such, there exists a need for an OTFT and capacitors that utilizes a dielectric that is biodegradable, high-k, exhibits low leakage current, and no hysteresis, while also being amenable to a variety of processing techniques, preferably in an environmentally friendly manner.
An object of the invention is to provide a polymer dielectric comprising a multi-layered structure containing at least two different dielectric materials, as well as organic thin-film transistors (OTFT) and capacitors comprising this multi-layered structure, and methods for crosslinking the dielectric materials.
According to an aspect of the invention described herein, there is provided a polymer dielectric comprising a multi-layered structure containing at least two different dielectric materials, wherein the dielectric materials comprise biodegradable organic dielectric materials.
In certain non limiting embodiments of the polymer dielectric, the polymer dielectric may contain two or three different dielectric materials.
In further non limiting embodiments of the polymer dielectric, the multi-layered dielectric may contain at least one low-k dielectric material and at least one high-k dielectric material.
In further non limiting embodiments of the polymer dielectric, the biodegradable organic dielectric materials may be crosslinked at an interface of the material interface.
In further non limiting embodiments of the polymer dielectric, the dielectric may comprise a capacitor or transistor, or a polymer capacitive sensor.
According to another aspect of the invention described herein, there is provided an organic thin-film transistor (OTFT) comprising:
According to yet another aspect of the invention described herein, there is provided a capacitor comprising:
In certain non limiting embodiments of the OTFT or capacitor described herein, the
multi-layered dielectric component may be comprised of at least two different dielectric materials;
In further non limiting embodiments of the OTFT or capacitor described herein, the multi-layered dielectric component may be comprised of at least one high-k dielectric material and at least one low-k dielectric material.
In other non limiting embodiments of the OTFT or capacitor described herein, the multi-layered dielectric component may consist of only organic dielectric materials;
In further non limiting embodiments of the OTFT or capacitor described herein, the multi-layered dielectric component may consist of only biodegradable materials;
In additional non limiting embodiments of the OTFT or capacitor described herein, the multi-layered dielectric component may comprise:
In other non limiting embodiments of the OTFT or capacitor described herein, the PVAc layer and TPCL may be thermally cross-linked to one another.
In yet further non limiting embodiments of the OTFT or capacitor described herein, the multi-layered dielectric component may comprise:
In non limiting embodiments of the OTFT or capacitor described above, the TPCL layer may be deposited above the PVAc layer, and the PVAc layer deposited above the PLA layer.
In yet other non limiting embodiments of the OTFT or capacitor described herein, the PVAc layer and TPCL may be thermally cross-linked to one another.
According to yet another aspect of the invention described herein, there is provided a method for preparing a multi-layer dielectric for an organic thin-film transistor (OTFT) or capacitor, wherein:
In non limiting embodiments of the described method, the high-k dielectric material may be a poly (vinyl alcohol)/cellulose nanocrystal blended dielectric (PVAc) and the low-k dielectric material may be a toluene diisocyanate-terminated polycaprolactone (TPCL), and the TPCL layer is crosslinked with the PVAc material via hydroxyl groups of the PVAc material.
In further non limiting embodiments of the described method, the low-k dielectric material layer may be crosslinked on top of the high-k dielectric material at a layer interface after deposition.
In yet further non limiting embodiments, the crosslinking temperature is carried out at or above crosslinking temperatures, and below a decomposition temperature of the specific polymer used. For example, in non limiting embodiments the crosslinking may be carried out at from 150° C. to 350° C., more preferably from 150° C. to 250° C. In yet other non limiting embodiments of the described method, the crosslinking may be carried out at about 200° C.
These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:
One or more currently preferred embodiments have been described by way of example. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims.
Limitations in existing OTFT capabilities are overcome through the novel combination of multiple dielectric materials in a layered structure.
The layering of differing dielectric materials permits greater adaptability of OTFTs. It further enables the negative aspects of some dielectric materials, such as gate leakage, low-k properties, unfavorable surface chemistry, or moisture sensitivity, to be reduced such that they are suitable for use in a wider range of applications.
In an embodiment of the invention, the multiple dielectric layer (5) is made up of a mix of organic dielectric materials. In a preferred embodiment, PVA is used as a dielectric, and its dielectric properties are improved by combining it with a second dielectric that acts to protect it from water exposure. In certain embodiments, the addition of the second dielectric layer also changes the surface chemistry from hydrophilic to hydrophobic. This is especially helpful in an OTFT when depositing the next layer, which will form better on hydrophobic surfaces. This can lead to improved OTFT performance, and better manufacturability of the device. In a particularly preferred embodiment, the PVA layer is further protected by first cross-linking PVA with cellulose nanocrystals.
A particularly preferred embodiment of the invention is exemplified in
In a further particularly preferred embodiment, the PVAc layer (5a) is thermally cross-linked to the TPCL layer (5b).
Without being limited by any particular mechanism, it is believed that in this particularly preferred embodiment the PVAc layer (5a) has limited exposure to moisture, which reduces gate leakage that would otherwise be present in an OTFT where the sole dielectric was PVAc. It is believed that the layering of the multiple dielectric layer (5) permits a high-k polymer dielectric to be covered with a thin-film of a low-k material and thereby reduces the dipolar disorder at the dielectric/organic semiconductor interface, reducing charge trapping and the leakage current, all while preserving the large capacitance values obtained from high-k polymer dielectrics.
Alternative embodiments of the invention can utilize varying combinations high-k and low-k dielectrics, of either organic or inorganic nature, so as to optimize the desired characteristics of the resulting multiple dielectric layer (5).
Benefits of the invention are also available through further layering of dielectric materials. As shown in
Without being limited by any particular mechanism, it is believed that in this tri-layer embodiment of the invention, the use of a PLA layer (5c) and TPCL layer (5b) (both of which are low-k dielectrics) to encompass a central high-k PVAc layer (5a) further isolates the
PVAc layer (5a), minimizing the opportunity for dipolar disorder at the dielectric/organic semiconductor interface, and further reducing charge trapping and leakage current.
In a particularly preferred embodiment, the use of a multiple dielectric layer (5) permits the creation of an electronic component, for example but not limited to a sensor, exhibiting high-k, low leakage current, and no hysteresis, from otherwise unsuitable organic dielectrics. This provides an electronic component (e.g. a sensor) that is highly flexible and capable of being processed using a variety of substrate types (including rigid and flexible substrates) without need for costly or complex manufacturing equipment. In a particularly preferred embodiment, the dielectric materials found in the multiple dielectric layer (5) are all non-toxic and biodegradable, making this OTFT design desirable for use in food packaging.
Another tri-layer embodiment of the invention is illustrated in
When dielectrics are layered in accordance with this invention, the beneficial properties of high-k dielectrics remain available, while the commonly associated limitations (such as excessive gate leakage and sensitivity to moisture) that prevent high-k dielectrics from seeing wide-spread adoption in OTFTs are minimized. The result is an optimized dielectric component of the OTFT.
The beneficial properties from use of a multiple dielectric layer (5) in accordance with the invention can be seen in
OTFT manufacturing process.
With regard to tri-layered dielectrics,
The following examples illustrate methods of manufacturing OTFTs in accordance with the invention. The skilled person would understand what modification would be required to accommodate different dielectric materials when generating the multiple dielectric layer (5) component from a different combination of dielectric materials. Choice of preferred dielectric materials are dependent upon the intended use and desired properties of the sensor.
The synthesis of difunctionalized diisocyanate polycaprolactone was conducted as described by Prisco et al (Preparation, Physico-Chemical Characterization, and Optical Analysis of Polyvinyl Alcohol-Based Films Suitable for Protected Cultivation. J. Appl. Polym. Sci. 2002, 86 (3), 622-632. https://doi.org/10.1002/app.10912).
Polycaprolactone diol (PCL, 0.98 g, 0.5 mmol) was dissolved in chloroform (10 mL) and placed under nitrogen atmosphere. Tolylene-2,4-diisocyanate (0.97 g, 5.6 mmol), dissolved in chloroform (3 mL), was added to the PCL solution. The reaction mixture was refluxed at 65° C. for 5 hours. The chloroform was evaporated under reduced pressure, and the obtained viscous oil was washed three times with petroleum ether. The product was dissolved in dichloromethane (2 mL) and precipitated in petroleum ether (50 mL). The precipitation was repeated twice.
The product (0.9 g) was obtained as a viscous oil, which was dried in vacuo. 1H-NMR (400 MHz. CDCl3): 1.30, 1.39, and 1.64 (—CH2—); 2.27 (—CH3); 2.31 (—CH2—); 3.88 and 4.06 (—CH2—O—); 6.56, 6.77, and 7.08 (C—H, arom) ppm. FT-IR: 1220 (C-N), 1553 (N-H), 1724 (C═O), and 2270 (N═C—O) cm-1.
PVAc dispersions were prepared in ambient conditions according to Tousignant et al. (Improving Thin-Film Properties of Poly (Vinyl Alcohol) by the Addition of Low-Weight Percentages of Cellulose Nanocrystals. Langmuir 2020, 36 (13) https://doi.org/10.1021/acs.langmuir.0c00068).
A final concentration of 80 mg/ml PVA and 0.75 wt % CNCs. Briefly, 320 mg of PVA was dissolved in 2400 μL of distilled water at 90° C. and filtered using a 0.45 μm filter, after which 1650 μL of a 2 wt % dispersion of CNCs in water was added. TPCL solutions in anhydrous toluene were prepared at concentrations of 10, 4 and 2 mg/ml in a nitrogen-filled glovebox. PCL 80K MW was dissolved at 35 mg/ml. PCL was weighed under ambient environment and dissolved in toluene.
Ultrapure semiconducting-enriched dispersions of single-walled carbon nanotubes (sc-SWNTs) were prepared with a poly (carbazole-alt-co-fluorene) polymer (PCF) in toluene according to Rice et al. (Polycarbazole-Sorted Semiconducting Single-Walled Carbon Nanotubes for Incorporation into Organic Thin Film Transistors. Adv. Electron. Mater. 2019,5 (1), 1-11. https://doi.org/10.1002/aelm.201800539)
The synthesis of PCF (Mn=65 kDa, Ð=2.7) was also performed according Rice et al., with dispersions prepared using plasma grown SWCNTs (Batch: RNB781-120, diameter: 0.9-1.5 nm) purchased from Raymor NanoIntegris. The PCF-SWCNT dispersion was not filtered to remove excess polymer prior to fabricating OTFT devices, with concentration of sc-SWCNTs adjusted so that the peak at 937 nm had an absorbance value of 2.0 a.u (Figure S3).
A Laurell WS-650-23 spin coater was used to deposit the PVAc and PCL films. A specialty coating systems G3P-8 spin coater was used to deposit the TPCL films. PVAC, PVAc/TPCL, and PVAc/PCL films were deposited on 1 in2 glass substrates. The substrates were cleaned in a bath sonicator for 5 minutes using detergent, distilled water, acetone, and methanol, sequentially. The PVAc films were deposited by spin coating (200 μL) at 3000 RPM for 90 s under ambient conditions, then annealed under vacuum at 150° C. for 1h to remove excess moisture. PCL layers were deposited (200 μL) at 2000 RPM for 90 s under ambient conditions. TPCL layers were deposited (200 μL) at 2000 RPM for 60 s in an inert environment, then annealed for 15 minutes at 200° C. under vacuum to thermally crosslink the TPCL to the PVAc film.
Embodiments of the invention described herein additionally involve a process for preparing a multi-layer dielectric which comprises crosslinking the solution-processable polymers. For example, the method may comprise thermally crosslinking the low-k dielectric material with the high-k dielectric material. In embodiments, this may involve the crosslinking of a toluene diisocyanate-terminated polycaprolactone (TPCL) layer with the hydroxyl groups of a poly (vinyl alcohol)/cellulose nanocrystal (CNC) blended dielectric (PVAc).
In this non limiting example, a low-k TPCL layer is crosslinked on top of a high-k blend of PVA and CNCs (PVAc). The TPCL layer was thermally crosslinked with hydroxyl groups in the PVAc blend at the bilayer interface after film deposition. Optical profilometry and microscopy studies were performed to determine the optimal TPCL concentration to yield consistent thin-films. Metal-insulator-metal (MIM) capacitors were fabricated with and without the TPCL layer and characterized under ambient conditions and after 30 minutes of exposure to 99% relative humidity (RH). Incorporation of the TPCL layer significantly decreased moisture sensitivity compared to neat PVAc. Thermally crosslinking the TPCL polymer with the hydroxyl groups of PVAc enables annealing above the Tm of PCL as the crosslinked TPCL films can no longer move freely on the surface of the PVAc film and self-aggregate. In certain preferred embodiments, which are non limiting, the crosslinking can be carried out at from 150° C. to 350° C., in particular from 150° C. to 250° C., preferably about 200° C.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2022/000047 | 8/19/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63291751 | Dec 2021 | US |
