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Additives and low-temperature printing processes can integrate various power-consuming and power-consuming electronic devices on flexible substrates at low cost.However, the production of complete electronic systems from these devices usually requires power electronic devices to convert between the various operating voltages of the devices.Passive components—inductors, capacitors, and resistors—perform functions such as filtering, short-term energy storage, and voltage measurement, which are essential in power electronics and many other applications.In this article, we introduce inductors, capacitors, resistors and RLC circuits screen-printed on flexible plastic substrates, and report the design process to minimize the series resistance of inductors so that they can be used in power electronic devices .The printed inductor and resistor are then incorporated into the boost regulator circuit.Manufacture of organic light-emitting diodes and flexible lithium-ion batteries. Voltage regulators are used to power the diodes from the battery, demonstrating the potential of printed passive components to replace traditional surface mount components in DC-DC converter applications.
In recent years, the application of various flexible devices in wearable and large-area electronic products and the Internet of Things1,2 has been developed.These include energy harvesting devices, such as photovoltaic 3, piezoelectric 4, and thermoelectric 5; energy storage devices, such as batteries 6, 7; and power-consuming devices, such as sensors 8, 9, 10, 11, 12, and light sources 13.Although great progress has been made in individual energy sources and loads, combining these components into a complete electronic system usually requires power electronics to overcome any mismatch between power supply behavior and load requirements.For example, a battery generates a variable voltage according to its state of charge.If the load requires a constant voltage, or higher than the voltage that the battery can generate, power electronics are required.Power electronics use active components (transistors) to perform switching and control functions, as well as passive components (inductors, capacitors, and resistors).For example, in a switching regulator circuit, an inductor is used to store energy during each switching cycle, a capacitor is used to reduce voltage ripple, and the voltage measurement required for feedback control is done using a resistor divider.
Power electronic devices that are suitable for wearable devices (such as pulse oximeter 9) require several volts and several milliamps, usually operate in the frequency range of hundreds of kHz to several MHz, and require several μH and several μH inductance and The capacitance μF is 14 respectively.The traditional method of manufacturing these circuits is to solder discrete components to a rigid printed circuit board (PCB).Although the active components of power electronic circuits are usually combined into a single silicon integrated circuit (IC), passive components are usually external, either allowing custom circuits, or because the required inductance and capacitance are too large to be implemented in silicon .
Compared with the traditional PCB-based manufacturing technology, the manufacturing of electronic devices and circuits through the additive printing process has many advantages in terms of simplicity and cost.First, since many components of the circuit require the same materials, such as metals for contacts and interconnections, printing allows multiple components to be manufactured at the same time, with relatively few processing steps and fewer sources of materials15.The use of additive processes to replace subtractive processes such as photolithography and etching further reduces process complexity and material waste16, 17, 18, and 19.In addition, the low temperatures used in printing are compatible with flexible and inexpensive plastic substrates, allowing the use of high-speed roll-to-roll manufacturing processes to cover electronic devices 16, 20 over large areas.For applications that cannot be fully realized with printed components, hybrid methods have been developed in which surface mount technology (SMT) components are connected to flexible substrates 21, 22, 23 next to the printed components at low temperatures.In this hybrid approach, it is still necessary to replace as many SMT components as possible with printed counterparts to obtain the benefits of additional processes and increase the overall flexibility of the circuit.In order to realize flexible power electronics, we have proposed a combination of SMT active components and screen-printed passive components, with special emphasis on replacing bulky SMT inductors with planar spiral inductors.Among the various technologies for manufacturing printed electronics, screen printing is particularly suitable for passive components because of its large film thickness (which is necessary to minimize the series resistance of metal features) and high printing speed, even when covering centimeter-level areas The same is true at times.Material 24.
The loss of passive components of power electronic equipment must be minimized, because the efficiency of the circuit directly affects the amount of energy required to power the system.This is especially challenging for printed inductors composed of long coils, which are therefore susceptible to high series resistance.Therefore, although some efforts have been made to minimize the resistance 25, 26, 27, 28 of the printed coils, there is still a lack of high-efficiency printed passive components for power electronic devices.To date, many reported printed passive components on flexible substrates are designed to operate in resonant circuits for radio frequency identification (RFID) or energy harvesting purposes 10, 12, 25, 27, 28, 29, 30, 31.Others focus on material or manufacturing process development and show generic components 26, 32, 33, 34 that are not optimized for specific applications.In contrast, power electronic circuits such as voltage regulators often use larger components than typical printed passive devices and do not require resonance, so different component designs are required.
Here, we introduce the design and optimization of screen-printed inductors in the μH range to achieve the smallest series resistance and high performance at frequencies related to power electronics.Screen-printed inductors, capacitors, and resistors with various component values ​​are manufactured on flexible plastic substrates.The suitability of these components for flexible electronic products was first demonstrated in a simple RLC circuit.The printed inductor and resistor are then integrated with the IC to form a boost regulator.Finally, an organic light-emitting diode (OLED) and a flexible lithium-ion battery are manufactured, and a voltage regulator is used to power the OLED from the battery.
In order to design printed inductors for power electronics, we first predicted the inductance and DC resistance of a series of inductor geometries based on the current sheet model proposed in Mohan et al. 35, and fabricated inductors of different geometries to confirm The accuracy of the model.In this work, a circular shape was chosen for the inductor because a higher inductance 36 can be achieved with a lower resistance compared to a polygonal geometry.The influence of ink type and number of printing cycles on resistance is determined.These results were then used with the ammeter model to design 4.7 μH and 7.8 μH inductors optimized for minimum DC resistance.
The inductance and DC resistance of spiral inductors can be described by several parameters: outer diameter do, turn width w and spacing s, number of turns n, and conductor sheet resistance Rsheet.Figure 1a shows a photo of a silk-screen printed circular inductor with n = 12, showing the geometric parameters that determine its inductance.According to the ammeter model of Mohan et al. 35, the inductance is calculated for a series of inductor geometries, where
(a) A photo of the screen-printed inductor showing the geometric parameters.The diameter is 3 cm.Inductance (b) and DC resistance (c) of various inductor geometries.The lines and marks correspond to calculated and measured values, respectively.(d,e) The DC resistances of inductors L1 and L2 are screen printed with Dupont 5028 and 5064H silver inks, respectively.(f,g) SEM micrographs of the films screen printed by Dupont 5028 and 5064H, respectively.
At high frequencies, the skin effect and parasitic capacitance will change the resistance and inductance of the inductor according to its DC value.The inductor is expected to work at a sufficiently low frequency that these effects are negligible, and the device behaves as a constant inductance with a constant resistance in series.Therefore, in this work, we analyzed the relationship between geometric parameters, inductance, and DC resistance, and used the results to obtain a given inductance with the smallest DC resistance.
Inductance and resistance are calculated for a series of geometric parameters that can be realized by screen printing, and it is expected that inductance in the μH range will be generated.The outer diameters of 3 and 5 cm, the line widths of 500 and 1000 microns, and various turns are compared.In the calculation, it is assumed that the sheet resistance is 47 mΩ/□, which corresponds to a 7 μm thick Dupont 5028 silver microflake conductor layer printed with a 400 mesh screen and setting w = s.The calculated inductance and resistance values ​​are shown in Figure 1b and c, respectively.The model predicts that both inductance and resistance increase as the outer diameter and the number of turns increase, or as the line width decreases.
In order to evaluate the accuracy of model predictions, inductors of various geometries and inductances were fabricated on a polyethylene terephthalate (PET) substrate.The measured inductance and resistance values ​​are shown in Figure 1b and c.Although the resistance showed some deviation from the expected value, mainly due to changes in the thickness and uniformity of the deposited ink, the inductance showed very good agreement with the model.
These results can be used to design an inductor with the required inductance and minimum DC resistance.For example, suppose an inductance of 2 μH is required.Figure 1b shows that this inductance can be realized with an outer diameter of 3 cm, a line width of 500 μm, and 10 turns.The same inductance can also be generated using 5 cm outer diameter, 500 μm line width and 5 turns or 1000 μm line width and 7 turns (as shown in the figure).Comparing the resistances of these three possible geometries in Figure 1c, it can be found that the lowest resistance of a 5 cm inductor with a line width of 1000 μm is 34 Ω, which is about 40% lower than the other two.The general design process to achieve a given inductance with a minimum resistance is summarized as follows: First, select the maximum allowable outer diameter according to the space constraints imposed by the application.Then, the line width should be as large as possible while still achieving the required inductance to obtain a high fill rate (Equation (3)).
By increasing the thickness or using a material with higher conductivity to reduce the sheet resistance of the metal film, the DC resistance can be further reduced without affecting the inductance.Two inductors, whose geometric parameters are given in Table 1, called L1 and L2, are manufactured with different numbers of coatings to evaluate the change in resistance.As the number of ink coatings increases, the resistance decreases proportionally as expected, as shown in Figures 1d and e, which are inductors L1 and L2, respectively.Figures 1d and e show that by applying 6 layers of coating, the resistance can be reduced by up to 6 times, and the maximum reduction in resistance (50-65%) occurs between layer 1 and layer 2.Since each layer of ink is relatively thin, a screen with a relatively small grid size (400 lines per inch) is used to print these inductors, which allows us to study the effect of conductor thickness on resistance.As long as the pattern features remain larger than the minimum resolution of the grid, a similar thickness (and resistance) can be achieved faster by printing a smaller number of coatings with a larger grid size.This method can be used to achieve the same DC resistance as the 6-coated inductor discussed here, but with a higher production speed.
Figures 1d and e also show that by using the more conductive silver flake ink DuPont 5064H, the resistance is reduced by a factor of two.From the SEM micrographs of the films printed with the two inks (Figure 1f, g), it can be seen that the lower conductivity of the 5028 ink is due to its smaller particle size and the presence of many voids between the particles in the printed film.On the other hand, 5064H has larger, more closely arranged flakes, making it behave closer to bulk silver.Although the film produced by this ink is thinner than the 5028 ink, with a single layer of 4 μm and 6 layers of 22 μm, the increase in conductivity is sufficient to reduce the overall resistance.
Finally, although the inductance (equation (1)) depends on the number of turns (w + s), the resistance (equation (5)) depends only on the line width w.Therefore, by increasing w relative to s, the resistance can be further reduced.The two additional inductors L3 and L4 are designed to have w = 2s and a large outer diameter, as shown in Table 1.These inductors are manufactured with 6 layers of DuPont 5064H coating, as shown earlier, to provide the highest performance.The inductance of L3 is 4.720 ± 0.002 μH and the resistance is 4.9 ± 0.1 Ω, while the inductance of L4 is 7.839 ± 0.005 μH and 6.9 ± 0.1 Ω, which are in good agreement with the model prediction.Due to the increase in thickness, conductivity, and w/s, this means that the L/R ratio has increased by more than an order of magnitude relative to the value in Figure 1.
Although low DC resistance is promising, evaluating the suitability of inductors for power electronic equipment operating in the kHz-MHz range requires characterization at AC frequencies.Figure 2a shows the frequency dependence of the resistance and reactance of L3 and L4.For frequencies below 10 MHz, the resistance remains roughly constant at its DC value, while the reactance increases linearly with frequency, which means that the inductance is constant as expected.The self-resonant frequency is defined as the frequency at which the impedance changes from inductive to capacitive, with L3 being 35.6 ± 0.3 MHz and L4 being 24.3 ± 0.6 MHz.The frequency dependence of the quality factor Q (equal to ωL/R) is shown in Figure 2b.L3 and L4 achieve maximum quality factors of 35 ± 1 and 33 ± 1 at frequencies of 11 and 16 MHz, respectively.The inductance of a few μH and the relatively high Q at MHz frequencies make these inductors sufficient to replace traditional surface-mount inductors in low-power DC-DC converters.
The measured resistance R and reactance X (a) and quality factor Q (b) of inductors L3 and L4 are related to frequency.
In order to minimize the footprint required for a given capacitance, it is best to use capacitor technology with a large specific capacitance, which is equal to the dielectric constant ε divided by the thickness of the dielectric.In this work, we chose barium titanate composite as the dielectric because it has a higher epsilon than other solution-processed organic dielectrics.The dielectric layer is screen printed between the two silver conductors to form a metal-dielectric-metal structure.Capacitors with various sizes in centimeters, as shown in Figure 3a, are manufactured using two or three layers of dielectric ink to maintain good yield.Figure 3b shows a cross-sectional SEM micrograph of a representative capacitor made with two layers of dielectric, with a total dielectric thickness of 21 μm.The top and bottom electrodes are one-layer and six-layer 5064H respectively.Micron-sized barium titanate particles are visible in the SEM image because the brighter areas are surrounded by the darker organic binder.The dielectric ink wets the bottom electrode well and forms a clear interface with the printed metal film, as shown in the illustration with higher magnification.
(a) A photo of a capacitor with five different areas.(b) Cross-sectional SEM micrograph of a capacitor with two layers of dielectric, showing barium titanate dielectric and silver electrodes.(c) Capacitances of capacitors with 2 and 3 barium titanate dielectric layers and different areas, measured at 1 MHz.(d) The relationship between the capacitance, ESR, and loss factor of a 2.25 cm2 capacitor with 2 layers of dielectric coatings and frequency.
The capacitance is proportional to the expected area. As shown in Figure 3c, the specific capacitance of the two-layer dielectric is 0.53 nF/cm2, and the specific capacitance of the three-layer dielectric is 0.33 nF/cm2.These values ​​correspond to a dielectric constant of 13.The capacitance and dissipation factor (DF) were also measured at different frequencies, as shown in Figure 3d, for a 2.25 cm2 capacitor with two layers of dielectric.We found that the capacitance was relatively flat in the frequency range of interest, increasing by 20% from 1 to 10 MHz, while in the same range, DF increased from 0.013 to 0.023.Since the dissipation factor is the ratio of energy loss to the energy stored in each AC cycle, a DF of 0.02 means that 2% of the power handled by the capacitor is consumed.This loss is usually expressed as the frequency-dependent equivalent series resistance (ESR) connected in series with the capacitor, which is equal to DF/ωC.As shown in Figure 3d, for frequencies greater than 1 MHz, ESR is lower than 1.5 Ω, and for frequencies greater than 4 MHz, ESR is lower than 0.5 Ω.Although using this capacitor technology, the μF-class capacitors required for DC-DC converters require a very large area, but the 100 pF-nF capacitance range and low loss of these capacitors make them suitable for other applications, such as filters and resonant circuits .Various methods can be used to increase the capacitance.A higher dielectric constant increases the specific capacitance 37; for example, this can be achieved by increasing the concentration of barium titanate particles in the ink.A smaller dielectric thickness can be used, although this requires a bottom electrode with a lower roughness than a screen-printed silver flake.Thinner, lower roughness capacitor layers can be deposited by inkjet printing 31 or gravure printing 10, which can be combined with a screen printing process.Finally, multiple alternating layers of metal and dielectric can be stacked and printed and connected in parallel, thereby increasing the capacitance 34 per unit area.
A voltage divider composed of a pair of resistors is usually used to perform voltage measurement required for feedback control of a voltage regulator.For this type of application, the resistance of the printed resistor should be in the kΩ-MΩ range, and the difference between the devices is small.Here, it was found that the sheet resistance of the single-layer screen-printed carbon ink was 900 Ω/□.This information is used to design two linear resistors (R1 and R2) and a serpentine resistor (R3) with nominal resistances of 10 kΩ, 100 kΩ, and 1.5 MΩ.The resistance between the nominal values ​​is achieved by printing two or three layers of ink, as shown in Figure 4, and photos of the three resistances.Make 8-12 samples of each type; in all cases, the standard deviation of the resistance is 10% or less.The resistance change of samples with two or three layers of coating tends to be slightly smaller than that of samples with one layer of coating.The small change in the measured resistance and the close agreement with the nominal value indicate that other resistances in this range can be directly obtained by modifying the resistor geometry.
Three different resistor geometries with different numbers of carbon resistive ink coatings.The photos of the three resistors are shown on the right.
RLC circuits are classic textbook examples of resistor, inductor, and capacitor combinations used to demonstrate and verify the behavior of passive components integrated into real printed circuits.In this circuit, an 8 μH inductor and a 0.8 nF capacitor are connected in series, and a 25 kΩ resistor is connected in parallel with them.The photo of the flexible circuit is shown in Figure 5a.The reason for choosing this special series-parallel combination is that its behavior is determined by each of the three different frequency components, so that the performance of each component can be highlighted and evaluated.Considering the 7 Ω series resistance of the inductor and the 1.3 Ω ESR of the capacitor, the expected frequency response of the circuit was calculated.The circuit diagram is shown in Figure 5b, and the calculated impedance amplitude and phase and measured values ​​are shown in Figures 5c and d.At low frequencies, the high impedance of the capacitor means that the behavior of the circuit is determined by the 25 kΩ resistor.As the frequency increases, the impedance of the LC path decreases; the entire circuit behavior is capacitive until the resonant frequency is 2.0 MHz.Above the resonance frequency, the inductive impedance dominates.Figure 5 clearly shows the excellent agreement between calculated and measured values ​​across the entire frequency range.This means that the model used here (where inductors and capacitors are ideal components with series resistance) is accurate for predicting circuit behavior at these frequencies.
(a) A photo of a screen-printed RLC circuit that uses a series combination of an 8 μH inductor and a 0.8 nF capacitor in parallel with a 25 kΩ resistor.(b) Circuit model including series resistance of inductor and capacitor.(c,d) The impedance amplitude (c) and phase (d) of the circuit.
Finally, printed inductors and resistors are implemented in the boost regulator.The IC used in this demonstration is Microchip MCP1640B14, which is a PWM-based synchronous boost regulator with an operating frequency of 500 kHz.The circuit diagram is shown in Figure 6a.A 4.7 μH inductor and two capacitors (4.7 μF and 10 μF) are used as energy storage elements, and a pair of resistors are used to measure the output voltage of the feedback control.Select the resistance value to adjust the output voltage to 5 V.The circuit is manufactured on the PCB, and its performance is measured within the load resistance and the input voltage range of 3 to 4 V to simulate the lithium-ion battery in various charging states.The efficiency of printed inductors and resistors is compared with the efficiency of SMT inductors and resistors.SMT capacitors are used in all cases because the capacitance required for this application is too large to be completed with printed capacitors.
(a) Diagram of voltage stabilizing circuit.(b–d) (b) Vout, (c) Vsw, and (d) Waveforms of current flowing into the inductor, the input voltage is 4.0 V, the load resistance is 1 kΩ, and the printed inductor is used to measure.Surface mount resistors and capacitors are used for this measurement.(e) For various load resistances and input voltages, the efficiency of voltage regulator circuits using all surface mount components and printed inductors and resistors.(f) The efficiency ratio of surface mount and printed circuit shown in (e).
For 4.0 V input voltage and 1000 Ω load resistance, the waveforms measured using printed inductors are shown in Figure 6b-d.Figure 6c shows the voltage at the Vsw terminal of the IC; the inductor voltage is Vin-Vsw.Figure 6d shows the current flowing into the inductor.The efficiency of the circuit with SMT and printed components is shown in Figure 6e as a function of input voltage and load resistance, and Figure 6f shows the efficiency ratio of printed components to SMT components.The efficiency measured using SMT components is similar to the expected value given in the manufacturer’s data sheet 14.At high input current (low load resistance and low input voltage), the efficiency of printed inductors is significantly lower than that of SMT inductors due to the higher series resistance.However, with higher input voltage and higher output current, resistance loss becomes less important, and the performance of printed inductors begins to approach that of SMT inductors.For load resistances >500 Ω and Vin = 4.0 V or >750 Ω and Vin = 3.5 V, the efficiency of printed inductors is greater than 85% of SMT inductors.
Comparing the current waveform in Figure 6d with the measured power loss shows that the resistance loss in the inductor is the main cause of the difference in efficiency between the printed circuit and the SMT circuit, as expected.The input and output power measured at 4.0 V input voltage and 1000 Ω load resistance are 30.4 mW and 25.8 mW for circuits with SMT components, and 33.1 mW and 25.2 mW for circuits with printed components.Therefore, the loss of the printed circuit is 7.9 mW, which is 3.4 mW higher than the circuit with SMT components.The RMS inductor current calculated from the waveform in Figure 6d is 25.6 mA. Since its series resistance is 4.9 Ω, the expected power loss is 3.2 mW.This is 96% of the measured 3.4 mW DC power difference.In addition, the circuit is manufactured with printed inductors and printed resistors and printed inductors and SMT resistors, and no significant efficiency difference is observed between them.
Then the voltage regulator is fabricated on the flexible PCB (the circuit’s printing and SMT component performance are shown in Supplementary Figure S1) and connected between the flexible lithium-ion battery as the power source and the OLED array as the load. According to Lochner et al. 9 To manufacture OLEDs, each OLED pixel consumes 0.6 mA at 5 V.The battery uses lithium cobalt oxide and graphite as the cathode and anode, respectively, and is manufactured by doctor blade coating, which is the most common battery printing method.7 The battery capacity is 16mAh, and the voltage during the test is 4.0V.Figure 7 shows a photo of the circuit on the flexible PCB, powering three OLED pixels connected in parallel.The demonstration demonstrated the potential of printed power components to be integrated with other flexible and organic devices to form more complex electronic systems.
A photo of the voltage regulator circuit on a flexible PCB using printed inductors and resistors, using flexible lithium-ion batteries to power three organic LEDs.
We have shown screen printed inductors, capacitors and resistors with a range of values ​​on flexible PET substrates, with the goal of replacing surface mount components in power electronic equipment.We have shown that by designing a spiral with a large diameter, filling rate, and line width-space width ratio, and by using a thick layer of low-resistance ink.These components are integrated into a fully printed and flexible RLC circuit and exhibit predictable electrical behavior in the kHz-MHz frequency range, which is of greatest interest to power electronics.
Typical use cases for printed power electronic devices are wearable or product-integrated flexible electronic systems, powered by flexible rechargeable batteries (such as lithium-ion), which can generate variable voltages according to the state of charge.If the load (including printing and organic electronic equipment) requires a constant voltage or higher than the voltage output by the battery, a voltage regulator is required.For this reason, printed inductors and resistors are integrated with traditional silicon ICs into a boost regulator to power the OLED with a constant voltage of 5 V from a variable voltage battery power supply.Within a certain range of load current and input voltage, the efficiency of this circuit exceeds 85% of the efficiency of a control circuit using surface mount inductors and resistors.Despite material and geometric optimizations, resistive losses in the inductor are still the limiting factor for circuit performance at high current levels (input current greater than about 10 mA).However, at lower currents, the losses in the inductor are reduced, and the overall performance is limited by the efficiency of the IC.Since many printed and organic devices require relatively low currents, such as the small OLEDs used in our demonstration, printed power inductors can be considered suitable for such applications.By using ICs designed to have the highest efficiency at lower current levels, higher overall converter efficiency can be achieved.
In this work, the voltage regulator is built on the traditional PCB, flexible PCB and surface mount component soldering technology, while the printed component is manufactured on a separate substrate.However, the low-temperature and high-viscosity inks used to produce screen-printed films should allow passive components, as well as the interconnection between the device and the surface mount component contact pads, to be printed on any substrate.This, combined with the use of existing low-temperature conductive adhesives for surface mount components, will allow the entire circuit to be built on inexpensive substrates (such as PET) without the need for subtractive processes such as PCB etching.Therefore, the screen-printed passive components developed in this work help pave the way for flexible electronic systems that integrate energy and loads with high-performance power electronics, using inexpensive substrates, mainly additive processes and minimal The number of surface mount components.
Using Asys ASP01M screen printer and a stainless steel screen provided by Dynamesh Inc., all layers of passive components were screen printed on a flexible PET substrate with a thickness of 76 μm.The mesh size of the metal layer is 400 lines per inch and 250 lines per inch for the dielectric layer and the resistance layer.Use a squeegee force of 55 N, a printing speed of 60 mm/s, a breaking distance of 1.5 mm, and a Serilor squeegee with a hardness of 65 (for metal and resistive layers) or 75 (for dielectric layers) for screen printing.
The conductive layers—the inductors and the contacts of capacitors and resistors—are printed with DuPont 5082 or DuPont 5064H silver microflake ink.The resistor is printed with DuPont 7082 carbon conductor.For the capacitor dielectric, the conductive compound BT-101 barium titanate dielectric is used.Each layer of dielectric is produced using a two-pass (wet-wet) printing cycle to improve the uniformity of the film.For each component, the effect of multiple printing cycles on component performance and variability was examined.Samples made with multiple coatings of the same material were dried at 70 °C for 2 minutes between coatings.After applying the last coat of each material, the samples were baked at 140 °C for 10 minutes to ensure complete drying.The automatic alignment function of the screen printer is used to align subsequent layers.The contact with the center of the inductor is achieved by cutting a through hole on the center pad and stencil printing traces on the back of the substrate with DuPont 5064H ink.The interconnection between printing equipment also uses Dupont 5064H stencil printing.In order to display the printed components and SMT components on the flexible PCB shown in Figure 7, the printed components are connected using Circuit Works CW2400 conductive epoxy, and the SMT components are connected by traditional soldering.
Lithium cobalt oxide (LCO) and graphite-based electrodes are used as the cathode and anode of the battery, respectively.The cathode slurry is a mixture of 80% LCO (MTI Corp.), 7.5% graphite (KS6, Timcal), 2.5% carbon black (Super P, Timcal) and 10% polyvinylidene fluoride (PVDF, Kureha Corp.). ) The anode is a mixture of 84wt% graphite, 4wt% carbon black and 13wt% PVDF.N-Methyl-2-pyrrolidone (NMP, Sigma Aldrich) is used to dissolve the PVDF binder and disperse the slurry.The slurry was homogenized by stirring with a vortex mixer overnight.A 0.0005 inch thick stainless steel foil and a 10 μm nickel foil are used as current collectors for the cathode and anode, respectively.The ink is printed on the current collector with a squeegee at a printing speed of 20 mm/s.Heat the electrode in an oven at 80 °C for 2 hours to remove the solvent.The height of the electrode after drying is about 60 μm, and based on the weight of the active material, the theoretical capacity is 1.65 mAh/cm2.The electrodes were cut into dimensions of 1.3 × 1.3 cm2 and heated in a vacuum oven at 140°C overnight, and then they were sealed with aluminum laminate bags in a nitrogen-filled glove box.A solution of polypropylene base film with anode and cathode and 1M LiPF6 in EC/DEC (1:1) is used as the battery electrolyte.
Green OLED consists of poly(9,9-dioctylfluorene-co-n-(4-butylphenyl)-diphenylamine) (TFB) and poly((9,9-dioctylfluorene-2,7- (2,1,3-benzothiadiazole-4, 8-diyl)) (F8BT) according to the procedure outlined in Lochner et al. 9.
Use Dektak stylus profiler to measure film thickness.The film was cut to prepare a cross-sectional sample for investigation by scanning electron microscopy (SEM).The FEI Quanta 3D field emission gun (FEG) SEM is used to characterize the structure of the printed film and confirm the thickness measurement.The SEM study was conducted at an accelerating voltage of 20 keV and a typical working distance of 10 mm.
Use a digital multimeter to measure DC resistance, voltage and current.The AC impedance of inductors, capacitors and circuits are measured using Agilent E4980 LCR meter for frequencies below 1 MHz and Agilent E5061A network analyzer is used for measuring frequencies above 500 kHz.Use the Tektronix TDS 5034 oscilloscope to measure the voltage regulator waveform.
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