Printed patterns of thin film heaters on a quartz substrate using silver nanoparticle ink and its method of printing

Abstract

The present invention relates to the thin film heaters fabricated by direct ink writing method using silver nanoparticle ink on quartz substrate. Three different structures of thin film heaters are being fabricated, namely, serpentine, spiral, and combination of both spiral and serpentine. These structures help provide varied temperature distribution over the heater surface, while conserving costly ink material. Temperature distributions can be readily controlled by varying the patterns and the applied voltages. The printed thin film heater is a good replacement for the conventional thin film heater fabricated by physical vapour deposition. Printing helps in conserving costly precursor material, is less expensive, takes less time for fabrication and is versatile in producing different designs without the need for expensive masks. These printed thin films can be calibrated and used as heaters for gas sensing.

Description

[0001] IITM-IDF3075

[0002] PRINTED PATTERNS OF THIN FILM HEATERS ON A QUARTZ SUBSTRATE USING SILVER NANOPARTICLE INK AND ITS METHOD

[0003] OF PRINTING

[0004] FIELD OF INVENTION:

[0005]

[0001] The present invention relates to the field of thin film heaters. More particularly, the present invention relates to the printed patterns of thin film heaters on a quartz substrate using silver nanoparticle ink and its method of printing.

[0006] DESCRIPTION OF THE RELATED ART:

[0007]

[0002] Printed thin film heaters provide versatile and efficient heating solutions in a variety of industries, including automotive, medical, sensor technology, and consumer electronics. They have several advantages over traditional heating elements, including lightweight construction, flexibility, and the ability to integrate with a variety of substrates. This makes them ideal for modern technological applications that require space and weight while also improving efficiency and substrate integration. These heaters, which use advanced materials and printing technologies, provide efficient and uniform heating over large areas while also being flexible, quick to respond, and durable. They are especially well-suited for portable and wearable thermal management applications, which improve thermal solutions across a wide range of industries. Flexible printed heaters, such as tracebased designs, can provide uniform heating by adjusting the width, gap, and external traces, resulting in efficient and precise heating.

[0008]

[0003] Material science advancements have accelerated the development of printed thin film heaters, particularly with conductive inks and polymers, allowing for precise deposition of conductive inks such as AgNW / PEDOT:PSS for flexible, biocompatible printed heaters and bioelectronics, whereas silver nanoparticle inks are preferred for 3D printed electronics. Electrically conductive 2D material coatings, such as graphene and MXenes, enable flexible and stretchable printed thin film heaters. This advances lightweight electronic components and sensor applications. Silver nanoparticle-decorated multiwalled carbon nanotube ink with PEDOT:PSS enables the fabrication of advanced wearable devices like strain sensors, smart gloves, heaters, and breath sensors, demonstrating exceptional performance characteristics. Conductive inks, including AgNW7PED0T:PSS, silver nanoparticles, silver nanowires inks and graphene / CNT materials, improve the flexibility, conductivity, and biocompatibility of printed thin film heaters. Ag nanoparticles, Cu@Ag core-shell nanoparticles, graphene, and CNT inks enhance the flexibility and conductivity of printed thin film heaters, sensors, and bioelectronics, leading to advancements in wearable electronics.

[0009]

[0004] These inks can be deposited in precise patterns using different printing techniques. Screen printing is an inexpensive method of creating two-dimensional patterns on substrates such as fabric, acrylic, and metal plates. It supports a wide range of functional materials, including conductive and dielectric inks that require high viscosity and low volatility. The film thickness is influenced by mesh size, scanning speed, pressure force, screen-substrate distance and ink properties. Inkjet printing is a material-conserving technique that deposits nanomaterials through micrometer-sized nozzles to create functional patterns. The challenges include printability, line defects, resolution sensitivity, reproducibility, material waste, and the need for continuous calibration. Direct Ink Writing (DIW) technology facilitates the development of electronic devices by allowing rapid and convenient printing of structures with specific functions. Unlike traditional electronic manufacturing methods, DIW allows for robust 3D structure design without harsh chemicals or high-temperature processes, enhancing user-friendliness and versatility. The use of diverse materials, structures, and methods, as well as printable conducting inks with specific rheology, could lead to highly embedded electronics, flexible devices, and wearable systems. This marks a significant shift in electronics manufacturing and multi-material printing, as well as optimized fabrication with increased efficiency. These methods enable the creation of heaters that are not only efficient but also versatile in terms of shape, size, and heating characteristics.

[0010]

[0005] Reference may be made for the following:

[0011]

[0006] Patent No. US11304263 provides an apparatus, system and method for a flexible heater suitable for embedding in a wearable. The flexible heater comprises a conformable substrate; a matched function ink set, printed onto at least one substantially planar face of the substrate to form at least a conductive layer capable of receiving current flow from at least one power source; a resistive layer electrically associated with the at least one conductive layer and comprising a plurality of heating elements capable of generating heat upon receipt of the current flow; and a dielectric layer capable of at least partially insulating at least one resistive layer, wherein the matched ink set is matched to preclude detrimental interactions between the printed inks of each of the at least one conductive, resistive and dielectric layers, and to preclude detrimental interactions with the conformable substrate.

[0012]

[0007] Publication No. KR101584202 relates to a method for manufacturing a PTC planar heater using PTC ink for gravure. According to the present invention, a flexible planar heater produced based on a printing operation with conductive silver ink and PTC carbon ink is manufactured using gravure equipment, thereby being usable in various heating and heater fields such as a car seat heater, a steering wheel heater, a mirror heater for removing frost, a room heating film and an electric pad.

[0013]

[0008] Publication No. W02024050334 relates to a tailored thermal body including a substrate and a plurality of material regions extending throughout the substrate, the plurality of material regions having a variable thermal conductivity. At least one heating element is secured to the substrate. The substrate and the plurality of material regions are formed using at least one additive manufacturing process, and materials of the substrate and the plurality of material regions are chemically fused together.

[0014]

[0009] Publication No. US2007007267 relates to a method and apparatus for manufacturing thin film heaters. The method and apparatus include an automated process for applying at least one conductor to a conductive substrate, where the conductor and the conductive substrate are in electrical communication. In alternate embodiments, a flexographic printing process is used to overlay two similar layers of ink on a carbon impregnated substrate and cure the ink to form at least one electrode conductor.

[0010] Patent No. US11680180 relates to methods for forming e-textiles, wherein the methods include printing a particle-free conductive ink on a textile substrate and curing the textile substrate to produce a conductive pattern thereon. The printing may include inkjet printing and may produce a printed pattern which exhibits an ink bleed of less than 0.5 mm, such as less than 0.2 mm. During printing, the textile substrate may be heated to a temperature of 30° C to 90° C before and during the printing process. The fabric substrate may be cured using heat and / or light to produce a conductive pattern having a sheet resistance of less than 10 Q / square, or even less than 1 Q / square.

[0015] [OH] Patent No. US11064572 relates to a three-dimensional (3D) printed heater may include a part body formed of fused thermoplastic polymer particles and an electrically resistive element formed of a matrix of conductive particles interspersed between a matrix of thermoplastic polymer particles. The conductive particles and the thermoplastic polymer particles may be provided at respective densities to cause the electrically resistive element to have a predetermined resistance level.

[0016]

[0012] Publication No. US2022155247 relates to a gas sensing device, which is manufactured with three dimensionally connected metal oxide foam structure of large surface area and elongated channel pores within the three-dimensional porous structure for gas sensing applications, thereby increasing the surface area of the sensing layer and expediting sensitivity and sensor response. A gas sensor device includes the fabricated metal-oxide-foam sensing material attached via silver paste to platinum electrodes and a ruthenium heater that are printed on low temperature co-fired ceramic substrate.

[0017]

[0013] Publication No. CN210518867 relates to a conductive printed circuit, which is distributed on a base body, lead terminals are arranged at the two ends of the conductive printed circuit. This circuit is used for being connected with an external circuit and heating the assembly and it comprises resin and metal powder. It is further covered with a front face protective film. The printing type heater assembly can heat quickly, and it reduces the cost, improves the heat exchange efficiency, guarantees automatic fusing during overheating, and is safer and more reliable.

[0014] Publication No. CN116056266 relates to an electric heater based on a metal nanoparticle electrode and a preparation method and its application thereof relates to the technical field of metal nanoparticle electrodes. A metal nanoparticle solution is spray ed / scraped / dispensed on the surface of a substrate, a grid network structure is formed through self-assembly under the action of capillary driving force, and a metal nanoparticle layer is endowed with conductivity in a hot-pressing mode and is transferred to the surface of a thin film. And after cooling, stripping the film on which the metal nanoparticle grid network is transferred from the surface of the substrate to obtain the metal nanoparticle grid network electric heater.

[0018]

[0015] Thus, the heater uses Joule heating to achieve desired properties such as low response time, high spatial uniformity, long-term stability, low operating voltage, consistent heating temperature, cyclic stability, and low power consumption. Functional inks typically use resistive and conductive materials, such as carbon or silver. Silver nanoparticle ink is used to print thin film heaters due to its higher electrical conductivity and resistance to oxidation. Resistive heating elements in printed patterns can convert electrical energy into heat when an electric current passes through them, like how conventional heaters work. Printed heaters offer advantages over wire-based flexible heaters, including lower manufacturing costs, lower operating power, and greater flexibility due to a thin coating of tens of microns, good local temperature control. The challenge in heater design is to achieve uniform heating in a required heating area, which can be accomplished using a variety of design patterns ranging from basic wire patterns to complex shaped patterns that provide uniform thermal distribution. The serpentine, fan type, and double spiral square micro-heaters use less power, while the serpentine and double spiral provide better temperature distribution. The spiral square pattern is more efficient for higher temperatures. However, further improvements are needed to achieve uniform thermal distribution.

[0019]

[0016] To overcome the above listed prior art, the present invention aims to provide printed patterns of thin film heaters on a quartz substrate using silver nanoparticle ink and its method of printing OBJECTS OF THE INVENTION:

[0020]

[0017] The principal object of the present invention is to provide printed patterns of thin film heaters on a quartz substrate using silver nanoparticle ink and its method of printing.

[0021]

[0018] Another object of the present invention is to provide a pattern that has uniform temperature distribution and consumes the least amount of silver nanoparticle ink for printing.

[0022]

[0019] Another object of the present invention is to provide printed patterns showing good sensitivity.

[0023]

[0020] Yet another object of the present invention is to provide patterns for heaters that have good mechanical flexibility and durability during repeated thermal cycling tests.

[0024]

[0021] Still another object of the present invention is to provide silver nanoparticle ink printed as thin film heaters, which can be utilized in sensors, biomedical devices, and automotive systems.

[0025] SUMMARY:

[0026]

[0022] The present invention relates to the printed patterns of thin film heaters on a quartz substrate using silver nanoparticle ink and its method of printing. The encapsulant polydimethylsiloxane (PDMS) is printed, which is used for environmental protection, using the direct writing technique. The spiral, serpentine, and spiral-serpentine patterns have uniform temperature distribution and consume the least amount of silver nanoparticle ink for printing. The heaters have good mechanical flexibility and durability during repeated thermal cycling tests. The silver nanoparticle ink printed as thin film heaters has great potential for utilization in sensors, biomedical devices, and automotive systems.

[0027]

[0023] The heaters are fabricated by direct ink writing of a commercial silver nanoparticle ink on a quartz substrate and the number of printed layers and volume per layer are optimized to achieve good electrical conductivity. The encapsulant poly dimethylsiloxane (PDMS) is printed over the heater pattern and the heater’s performance is evaluated up to 200°C. The heaters have good stability and cyclability and among the different heater patterns. The combined serpentine-spiral pattern provides more uniform temperature distribution while using less ink. This can be used as a heater design for different applications, such as a heater for metal oxide-based gas sensing.

[0028] BREIF DESCRIPTION OF THE INVENTION

[0029]

[0024] It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments.

[0030]

[0025] Figure 1 (a,b,c) shows thin film heater design patterns

[0031]

[0026] Figure 2 shows printing procedure of AgNp thin film patterns

[0032]

[0027] Figure 3 (a,b,c) the actual image of the heater post encapsulation and silver epoxy contacts.

[0033]

[0028] Figure 4 shows IR images of temperature distribution of different types of heaters at 11 V (a) serpentine, (b) spiral, and (c) spiral and serpentine

[0034]

[0029] Figure 5 shows serpentine heater: (a) Temperature distribution for different applied voltages of 1-11 V with a step size of 2 V for on and off time of 300 s each, (b) Current and resistance for applied voltages of 1-11 V with a step size of 2 V for 300 s, (c) Temperature vs Observed resistance

[0035]

[0030] Figure 6 shows spiral heater: (a) Temperature distribution for different applied voltages of 1-11 V with a step size of 2 V for on and off time of 300 s each, (b) Current and resistance for applied voltages of 1-11 V with a step size of 2 V for 300 s, (c) Temperature vs Observed resistance

[0031] Figure 7 shows spiral and serpentine heater: (a) Temperature distribution for different applied voltages of 1-11 V with a step size of 2 V for on and off time of 300 s each, (b) current and resistance for applied voltages of 1-11 V with a step size of 2 V for 300 s, (c) Temperature vs Observed resistance

[0036]

[0032] Figure 8 shows (a) Spiral-serpentine heater: heating and cooling cycles, (b) Temperature response of heater under continuous gradient voltage, (c) Normalized resistance of the heater as a function of voltage at different heating cycles

[0037]

[0033] Figure 9 shows the standard deviation error bar for applied voltage in terms of resistance (a) and temperature (b).

[0038] DETAILED DESCRIPTION OF THE INVENTION:

[0039]

[0034] The present invention provides printed patterns of thin film heaters on a quartz substrate using silver nanoparticle ink and its method of printing. The encapsulant PDMS is printed, which is used for environmental protection, using the direct writing technique. The spiral, serpentine, and spiral-serpentine patterns have uniform temperature distribution and consume the least amount of silver nanoparticle ink for printing. The heaters have good mechanical flexibility and durability during repeated thermal cycling tests. The silver nanoparticle ink printed as thin film heaters has great potential for utilization in sensors, biomedical devices, and automotive systems.

[0040]

[0035] The heaters are fabricated by direct ink writing of a commercial silver nanoparticle ink on a quartz substrate and the number of printed layers and volume per layer are optimized to achieve good electrical conductivity. The encapsulant PDMS is printed over the heater pattern and the heater’s performance is evaluated up to 200 °C. The heaters have good stability and cyclability and among the different heater patterns the combined serpentine-spiral pattern provide more uniform temperature distribution while using less ink. This can be used as a heater design for different applications, such as a heater for metal oxide-based gas sensing.

[0041]

[0036] PDMS was used as an encapsulant because of its outstanding optical transparency, elasticity, biocompatibility, hydrophobicity, and durability, which are all due to the strong covalent bond between silicon and oxygen. This is prepared by combining base to curing agent in the ratio of 10: 1. Silver epoxy is used for making contacts.

[0042]

[0037] The pointer is built using silver nanoparticle (Ag NP) ink and DIW on a quartz substrate, with key parameters like printed layer thickness, volume per layer, and conductivity optimized for better performance. The conductivity values ranged from 3.42 * 107Q-1m-1to 3.47 * 107Q-1m-1, depending on the number of printing passes, compared to the bulk silver conductivity of 6.3 x io7Q-1m-1. Sheet resistance values of 0.57, 0.37, and 0.32 Q / square were obtained with film thicknesses of 5.4 ± 1.8 pm, 7.84 ± 0.4 pm, and 8.98 ± 1.1 pm for 1, 2, and 3 printing passes respectively.

[0043]

[0038] Thermal performance analysis at an applied voltage of 11 V revealed that each heater design had different maximum temperatures and resistances. The serpentine design, with its winding path, reached the highest temperature of 196 °C and had a low resistance of 16.2 Q. This higher temperature is most likely due to the serpentine design’s efficient distribution of current. In comparison, the spiral design (Figure lb) with a circular pathway reached a maximum temperature of 159 °C and had a higher resistance of 31.7 Q. The spiral-serpentine design, which combines elements of both patterns, achieved a maximum temperature of 137.5 °C and resistance of 24.5 Q. This combined design allows current to flow along both winding and circular paths, lowering the maximum temperature while maintaining moderate resistance.

[0044]

[0039] At a lower 9 V, the serpentine heater drew the most current (426.89 mA), followed by the combination design (290.38 mA) and the spiral (229.11 mA).

[0045]

[0040] At 11 volts, the current values increased to 491.36 mA, 339.17 mA, and 268.16 mA for serpentine, combination, and spiral designs. These differences in current draw correspond to each design’s thermal and electrical properties, with the serpentine’s lower resistance drawing higher currents and producing more heat.

[0046]

[0041] The spiral -serpentine design (Figure 1c) strikes a balance between temperature and resistance, making effective use of a moderate amount of ink (1.17 pL), thereby managing thermal performance while optimizing material efficiency.

[0047] This can be used in wearable electronics, flexible heating elements and metal oxidebased gas sensor.

[0048]

[0042] The serpentine and spiral heater patterns provide uniform temperature distribution, and the combination of both heater patterns adds an advantage to their performance at high temperatures. Figure la shows serpentine pattern. This pattern maximizes the length of the heating element in a confined space, allowing for uniform temperature distribution. The spiral pattern consists of a continuous winding of the heating element in a spiral shape, making it suitable for applications requiring a compact heating element, such as small sensors or medical devices. The spiral-serpentine pattern improves heat distribution through efficient space utilization and optimal distribution.

[0049]

[0043] The Silver nanoparticle (Ag-NP) ink was deposited using the direct writer with a nozzle diameter of 220 pm. The Ag NP ink was sonicated for 15 min in a bath ultrasonicator prior to printing to ensure the particles are well dispersed in the solvent and does not clog the nozzle while printing.

[0050]

[0044] The Ag-NP ink is used for printing thin film heaters in this experiment. PDMS is used as an encapsulant because of its outstanding optical transparency, elasticity, biocompatibility, hydrophobicity, and durability, which are all due to the strong covalent bond between silicon and oxygen. It is a widely used flexible material for substrates and encapsulation. This is prepared by combining base to curing agent in the ratio of 10: 1. Silver epoxy is used for making contacts and custom-built direct ink writer used for printing includes a print bed (that can be heated up to 80 °C) and syringe-based extruder heads with controllable extrusion rates.

[0051]

[0045] Fabrication of Ag NP thin film heater patterns

[0052]

[0046] The silver ink vortexed and ultrasonicated for 15 min before printing. The 5 cm x 5 cm quartz substrates were first thoroughly cleaned using acetone followed by isopropyl alcohol (IP A) and UV treated for 30 min. A custom-built direct ink writer was used to print the heater patterns. The Direct ink writer, used for printing, includes a print bed (that can be heated up to 80 °C) and syringe-based extruder heads with controllable extrusion rates. The heater pattern was printed by loading the design data and the printing parameters using Dwrite software into the direct ink writer. Printing parameters for heater patterns include print bed temperature at 60 °C, printing speed at 20 mm / s, and Ag NP extrusion amount at 3 nL / mm. Stepper motors attached to the extruder heads were used for ink extrusion. The substrate was secured to the stage during printing. After the first pass of printing, the pattern is allowed to dry on the stage for a few minutes before we print the second pass. The printed pattern was annealed at 200 °C for 1 hour in a hot air oven. Following that, a rectangular pattern of PDMS encapsulant, measuring 22.36 mm x 29.10 mm, was printed over the heater and cured for 2 hours at 80 °C in a hot air oven. Electrical connections were made using silver epoxy and copper wires and curing epoxy was done at 60 °C. Heating performance of the printed Ag NP heaters was measured by an IR thermal camera. Figure 3 shows the actual image of the heater post encapsulation and silver epoxy contacts. Room temperature electrical resistance of the printed patterns was measured using a multimeter as 16.2 £1, 31.7 Q, 37.0 Q for serpentine, spiral and spiral-serpentine respectively. Film thickness was measured using Burker surface profilometer for 2 pass heater and is observed as 7.84± 0.4 pm. Around 3 nL of ink is used for printing per mm of thin film pattern. Actual volume of ink utilized is calculated as shown in Table 1.

[0053]

[0047] Table 1 : Volume of ink utilization

[0054]

[0048] Thin film heater testing was performed on an experimental testing setup consisting of a printed heater, source meter and IR camera. Experiment was carried by applying varying voltage from 1 to 11 V with a step size of 2 V recording real time temperature in the IR camera over a period of 300 s to measure the temperature distribution of thin film heater as a function of time.

[0055]

[0049] Surface morphology of the Ag ink shows uniform distribution of nanoparticles in the ink. Thickness of the printed Ag NP ink for 1, 2, and 3 passes shows an increase in thickness as number of passes are increased. This cumulative effect is expected in layered printing processes, where multiple passes result in a thicker overall printed structure.

[0056]

[0050] The maximum temperatures of serpentine, spiral, and spiral-serpentine heaters at 11 V (Figure 4 196 °C, 159 °C, and 137.5 °C, respectively) are influenced by their geometric designs, which affect electrical resistance, heat generation, and heat dissipation. The serpentine design produces the most heat due to its lower resistance, whereas the spiral design dissipates heat more efficiently, and the spiralserpentine design balances the two effects. Heating performance of the printed Ag- NP heaters was measured by an IR thermal camera.

[0057]

[0051] Joule heating occurs when the current flows through a heater, causing the temperature to rise. When the voltage is turned off, the heater cools to room temperature.

[0058]

[0052] Figure 4 shows IR images of Temperature distribution of different types of heaters at 11 V (a) serpentine, (b) spiral, and (c) spiral and serpentine

[0059]

[0053] Figure 5 shows serpentine heater: (a) temperature distribution for different applied voltages of 1-11 V with a step size of 2 V for on and off time of 300 s each, (b) current and resistance for applied voltages of 1-11 V with a step size of 2 V for 300 s, (c) temperature Vs observed resistance

[0060]

[0054] Figure 6 shows spiral heater: (a) temperature distribution for different applied voltages of 1-11 V with a step size of 2 V for on and off time of 300 s each, (b) current and resistance for applied voltages of 1-11 V with a step size of 2 V for 300 s, (c) temperature Vs observed resistance

[0061]

[0055] Figure 7 shows spiral-serpentine heater: (a) temperature distribution for different applied voltages of 1-11 V with a step size of 2 V for on and off time of 300 s each, (b) current and resistance for applied voltages of 1-11 V with a step size of 2 V for 300 s, (c) temperature Vs observed resistance

[0056] Figure 8 shows (a) spiral-serpentine heater heating and cooling cycles, (b) temperature response of heater under continuous gradient voltage, (c) normalized resistance of the heater as a function of voltage at different heating cycles.

[0062]

[0057] Ag NP ink is a conductive ink which is used due to its high electrical, thermal conductivity and low cost as compared to other materials. Ag-based inks can be printed onto a variety of substrates to create conductive patterns. Ag NP ink shows good stability at higher temperatures also (up to) 200 °C. Serpentine, Spiral and Spiral- Serpentine heaters can reach temperature up to 196 °C, 159 °C, 137.5 °C respectively at 11 V. The volume of ink utilized for combination heaters is 1.17 / / L which is less as compared to other two heater patterns. The heater’s temperature response was evaluated under continuous gradient voltage and repeated heating and cooling cycles. As shown in Figure 2, the printing procedure of Ag NP thin film heater patterns are given below:

[0063]

[0058] Step 1

[0064]

[0059] The Ag NP ink was sonicated for 15 min in a bath ultrasonicated prior to printing to ensure the particles are well dispersed in the solvent and does not clog the nozzle (nozzle diameter: 220 pm) while printing.

[0065]

[0060] Step 2

[0066]

[0061] Dycotec DM-SIJ-3200 silver ink, purchased by Dycotec Materials, UK, was vortexed in a REMI CM / 101 plus mixer. 5 cm x 5 cm quartz substrates were first thoroughly cleaned using acetone followed by isopropyl alcohol (IP A) and UV treated for 30 min.

[0067]

[0062] Step 3

[0068]

[0063] The heater pattern was printed by loading the design data and the printing parameters using Dwrite software into the direct ink writer. Printing parameters for heater patterns include print bed temperature 60 °C, printing speed at 20 mm / s, and Ag NP extrusion amount at 3 nL / mm. Stepper motors attached to the extruder heads were used for ink extrusion. The substrate was secured to the stage during printing and was used to print the heater patterns. After the first pass of printing, the pattern is allowed to dry on the stage for a few minutes before we print the second pass.

[0069]

[0064] Step 4

[0070]

[0065] The printed patterns are annealed at 200 °C for 1 hour in a hot air oven.

[0071]

[0066] Step 5.

[0072]

[0067] Following that, a rectangular pattern of PDMS encapsulant, measuring 22.36 mm x 29.10 mm, was printed over the heater and cured for 2 hours at 80 °C in a hot air oven.

[0073]

[0068] Step 6.

[0074]

[0069] Electrical connection was made using silver epoxy and copper wires and curing of epoxy was done at 60 °C.

[0075]

[0070] The observed differences in maximum temperatures of the serpentine, spiral, and spiral-serpentine heaters at 11 V, as recorded by an IR camera. Geometric design and surface area of serpentine heater provides a larger surface area and a longer path for the current to travel. This increases resistance and generates heat, resulting in the highest maximum temperature of 196 °C. In comparison to the serpentine design, the spiral heater may have a more compact structure and a shorter path for current flow. This leads to less resistance and heat generation, resulting in a lower maximum temperature of 159 °C. The combination of spiral and serpentine designs most likely strikes a balance between the two, offering moderate resistance and heat generation. This produces a maximum temperature of 137.5 °C.

[0076]

[0071] Heat dissipation and distribution of serpentine heater design is longer and more convoluted path may cause hotspots and inefficient heat dissipation, resulting in a higher overall temperature.

[0077]

[0072] The spiral design improves heat distribution across the surface, reducing hotspots and lowering the maximum temperature. Spiral-serpentine design may provide intermediate heat dissipation characteristics by balancing the efficient distribution of the spiral with the concentrated heating of the serpentine.

[0073] The resistance of each heater design influences the amount of power converted to heat (P = V2 / R). The serpentine heater produces more heat for the same applied voltage due to its longer path and possibly higher resistance. Under the same conditions, the spiral heater produces less heat because its path is shorter and has lower resistance. The spiral-serpentine heater falls somewhere in the middle, offering moderate resistance and heat generation.

[0078]

[0074] Thus, maximum temperatures of the serpentine, spiral, and spiral-serpentine heaters at 11 V (196°C, 159°C, and 137.5°C, respectively) are influenced by their geometric designs, which affect electrical resistance, heat generation, and heat dissipation. The serpentine design produces the most heat due to its higher resistance, whereas the spiral design dissipates heat more efficiently, and the spiralserpentine design balances the two effects.

[0079]

[0075] Figures 5(c), 6(c) and 7(c) shows the I-V characteristics of serpentine, spiral, and spiral-serpentine heater patterns, respectively. The current measurements at 9 V were 426.9 ± 2.0 mA for the serpentine heater, 290.4 ± 5.5 mA for the spiralserpentine heater, and 229. l±0.5 mA for the spiral heater. These values correspond to the resistances of each design: the serpentine, with the lowest resistance (16.2 ), allows the most current flow, whereas the spiral, with the highest resistance (31.7 Q), draws the least current.

[0080]

[0076] The spiral-serpentine heater has a balanced performance due to its intermediate resistance (24.5 Q). This demonstrates how resistance directly influences current flow, power output, and heat generation.

[0081]

[0077] The temperature coefficient of resistance (a) was calculated from the slope of the plot change in resistance Vs temperature which is approximately 0.0017 7C for all the heater patterns, shown in Figures 5(b), 6(b) and 7(b) respectively. Bulk silver has a reported TCR of 3.8 x 10-3 / °C, while previous measurements on silver nanoparticles range from 1.62 to 2.15 x 10-3 / °C . Thus, the experimental value is in the acceptable range. Joule heating occurs when the current flows through a heater, causing the temperature to rise. When the voltage is turned off, the heater cools to room temperature.

[0078] Figures 5(a), 6(a), and 7(a) illustrate heater temperature variation over time. Temperature changes were measured for input voltages ranging from 1 to 11 V, with increments of 2 V. Constant voltage supply was provided for 300 s to enable the system to achieve steady-state temperature and subsequently the cooling down or recovery of the heater back to room temperature was observed for the next 300 s. It was observed that heaters reach room temperature within 300 s, showing a good recovery time for all patterns. Figure 8(a) demonstrates good repeatability of heater after heating and cooling for 300 s for ten cycles at 5 V. Figures 8(b) and (c) show the temperature change during cycling, as well as the corresponding resistance change based on voltage respectively. The plots demonstrate a constant temperature with minimal changes in normalized resistance good recovery and the heater maintains good repeatability across multiple voltages and resistance variations.

[0082]

[0079] Figure 9 shows the standard deviation error bar for applied voltage in terms of resistance (a) and temperature (b). The serpentine design has larger error bars, indicating greater variability, especially at lower voltages. In contrast, the spiral and spiral-serpentine designs have smaller error margins, indicating more stable resistance responses suitable for applications that require consistency. Each of the designs has relatively small temperature error bars, implying consistent measurements. However, the spiral-serpentine design has slightly lower temperature variability at higher voltages, implying better thermal stability. The spiral and spiral-serpentine designs appear to be better suited for applications requiring consistent resistance, whereas the spiral-serpentine design, with its lower temperature rise and stable readings, is particularly appropriate for applications requiring precise temperature control.

[0083]

[0080] Figure 4 demonstrates the real-time temperature recorded by the IR camera for all three heater patterns. These images show that the spiral-serpentine heater distributes heat more evenly across the entire pattern than the serpentine and spiral heaters.

[0081] Thus, maximum temperatures of the serpentine, spiral, and spiral-serpentine heaters at 11 V (196 °C, 159 °C, and 137.5 °C, respectively) are influenced by their geometric designs, which affect electrical resistance, heat generation, and heat dissipation. The serpentine design produces the most heat due to its higher resistance, whereas the spiral design dissipates heat more efficiently, and the spiralserpentine design balances the two effects.

[0084]

[0082] Numerous modifications and adaptations of the system of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the true spirit and scope of this invention.

Claims

IITM-IDF3075WE CLAIM:

1. Printed patern of thin film heaters on quartz substrate using silver nanoparticle ink by direct ink writing technique comprises- a) serpentine patern which produces the most heat due to its lower5 resistance, b) the spiral patern which dissipates heat more efficiently, c) the spiral-serpentine patern which balances the efficient distribution of the spiral with the concentrated heating of the serpentine.

2. The printed thin film heaters, as claimed in claim 1, wherein the heaters can10 achieve temperature sensitivity ranging from 19.16 ± 0.90°C / V, 14.57 ± 0.80 °C / V and 12.27 ± 0.70 °C / V, depending on the printed patern (serpentine, spiral, spiral-serpentine).

3. The heater, as claim 1, wherein the spiral-serpentine design has minimal deviation during repeated heating and cooling cycles.

4. The method of printing paterns of thin film heaters on a quartz substrate15 includes following steps- a) The silver nanoparticle (Ag-NP) ink was sonicated for 15 min in a bath ultrasonicated prior to printing to ensure the particles are well dispersed in the solvent and does not clog the nozzle while printing. b) Silver ink was vortexed, and quartz substrates were first thoroughly cleaned using acetone followed by isopropyl alcohol (IP A) and UV treated for 30 min. c) The heater patern was printed by loading the design data and the printing parameters into the direct ink writer d) Printing parameters for heater paterns include print bed temperature25 60°C, printing speed at 20 mm / s, and Ag NP extrusion amount at 3 nL / mm. e) Stepper motors atached to the extruder heads were used for ink extrusion.f) The substrate was secured to the stage during printing and was used to print the heater patterns. g) After the first pass of printing, the pattern is allowed to dry on the stage for a few minutes before we print the second pass. h) The printed patterns are annealed at 200°C for 1 h in a hot air oven. i) Following that, a rectangular pattern of PDMS (encapsulant) was printed over the heater and cured for 2 hours at 80°C in a hot air oven. j) Electrical connection was made using silver epoxy and copper wires and curing of epoxy was done at 60°C.

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