# Computational and Experimental Analysis of a Triode Microfuse with a WO3 Heater

Authors: Shovon Talukder
Journal: Journal of Sensors
 (2023)

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## Abstract

In this study, high-current-protecting multilayered thin film microfuses are designed and simulated using the MEMS-based tool of COMSOL multiphysics software and then fabricated and tested in the laboratory. Portable electronic devices are comprised of a secondary battery or DC charge source, and due to short circuit overcurrent, fire, and explosions can ensue. A protecting device should steadily cater to phenomena like overcurrent situations to avoid hazardous circumstances. The primary purpose of this investigation is to design a heater resistor with a negative temperature coefficient (NTC) to function as a low melting point-based alloy for the fuse element. A lead-tin (90Pb:10Sn wt.%) alloy has been employed as the low melting point-based fuse element, and tungsten oxide (WO3) is integrated with the layer as a heater resistor due to its negative temperature coefficient of resistance characteristics. The electro-thermo-mechanical behavior is assessed, and a three-dimensional structural modeling and simulation technique has been performed in both steady-state and transient conditions with varying physical and electrical parameters. The heat required to melt the fuse depends on heater geometry, and when we applied 2 A current to the 1 : 30 length and width ratio-based device, the heater achieved 600 K. Experimentally, nearly at 1 A current and above 4 V, the microfuse reached melting temperature and thus has been blown which provides a scope of controlling nearly 4 W of power electronic devices.


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## Body

## 1. Introduction

Due to its high energy density and high current supply per unit mass and volume, high-capacity lithium-ion batteries (LIBs), which are employed not only in portable electronics, such as computers and cell phones but also attract the most attention among electric or hybrid vehicles and energy storage systems [1–3]. Actually, LIBs’ superior performance and energy density have made them more attractive in all of these applications [4]. Furthermore, LIBs now dominate the battery market for portable electronic devices due to their inherent benefits over other battery systems, including high specific capacity and voltage [5], reduced memory [6, 7], outstanding cycling performance [8], low self-discharge [9], and a wide operating temperature range [10]. However, the low safety performance of lithium-ion (Li-ion) batteries is now impeding the further expansion of the LIBs market and its large-scale applications [11–13]. Small and medium-sized secondary batteries used in portable devices have recently evolved into adequate forms to meet the demands of energy storage systems, such as reliable driving [14], long-term use [15], and rapid charging and discharging [16]. However, frequent charging and discharging of lithium-ion batteries can result in unwanted overcurrent, overvoltage, overloads, and other issues [17–19]. When a battery is overcharged or discharged or is subjected to an external or internal short circuit, it is vulnerable to electrical abuse, resulting in a sequence of unfavorable electrochemical processes [20–22]. As a result, battery runaways [23], battery fire accidents [24], and battery explosions [25] are likely to happen and lead to a massive threat to the safety of users. In addition, substantial economic challenges for connected market sectors have arisen, as well as significant damage to LIB’s reputation has taken place [3, 26]. To avoid secondary battery fires and explosions caused by such electrical abuse, it is necessary to install a fuse that prevents current input from functioning when the incoming current rises from its rated value [27, 28]. Positive temperature coefficient (PTC) resistors and thermal fuses are the most common secondary protection devices [29]. Although PTC thermistors have two different operating modes: self-heating and sensing, problems such as delayed response time, finite breaking current, and significant leakage current must still need to be addressed [30]. In today’s energy networks, a high-capacity electric fuse is essential [31]. Fuse has been used in low- and medium-voltage distribution network electrical installations for many years, and their behavior has been thoroughly investigated. They usually function at a lower current than their nominal current or under excess or short-circuit currents for a brief period. The joule heating generated on the fuse element dissipates to the element’s surrounding environment during operation [32]. The fuse-blowing phenomenon and fuse mechanism have extensive applications in electronic devices in the scale of small to large applications like smartphones, tablet PCs, notebooks, to outdoor power tools and equipment, e-bikes, e-scooters, energy storage systems, etc. Especially in the small-scale application and providing a low-cost advantage in the medical sector, the fuse has been considerably used in power knees, electric toothbrushes, medical carts, blood, infusion warmers, blood pumps, and eye disease detection [33].Recently, 0.05 to 1.25 A low-rated current carbon nanotube (CNT) fiber-based miniature fuse has been fabricated in the form of a universal modular fuse (UMF) [34]. To operate and control 210-400% over current of the rated current a tin metal-based low melting plate subminiature fuse protection system has been presented for the safety of a direct current (DC) measurement device [35]. A simple structure made of In-Bi-Sn alloy-based thermally fusible parts for secondary battery systems which can operate at a maximum of 92.4°C is assembled from a simple process called tape casting for an application like a mobile telephone. A Pb-Sn-Ag alloy-based low-melting fuse element for preventing short circuits over current and also can sense the microcurrent change in a secondary battery with a capacity of nearly 2 W has been designed and fabricated for small power secondary batteries [36]. The current control capacity is only for low-capacity batteries and thus is not appropriate for high-capacity current protection applications available on the market. In all these cases, a requirement for high-temperature melting point-based and high-current controllable fuse devices for high-power secondary battery protection denotes as a motivation to study this current work.We have designed a triode microfuse by motivating from nanofabrication techniques and utilizing the advantage of excellent material available. The triode microfuse device is comprised of a stable substrate, a conducting electrode, a negative temperature coefficient (NTC) of resistance characteristics-based heater resistance, and an alloy as a fuse material. We have considered some parameters and attributes for selecting device material. Some of the features that conductive film materials should have included are good electrical properties [37, 38], thermal properties [39], solderability [40], a high melting point [41], and low oxidation [42]. Due to their low melting points, zinc, lead, and tin are not used as conductive materials [43, 44]. Copper has good thermal and electrical qualities, although it oxidizes quickly at exalted temperatures [45]. It might still be used provided the conductive film was shielded against oxidation, for example by utilizing inert protective coatings like graphene oxide-polymer composite [46]. Aluminium has poor thermal and electrical properties, and when exposed to air, it readily oxidizes [47]. Gold has excellent thermal and electrical qualities as well as chemical stability [48]. Gold has strong oxidation resistance, a high melting point, low electrical resistance, and high thermal conductivity [49] which makes it viable for using as a conductor in sensor design.Mechanically, conductive film materials should have good adhesion to the substrate, a low Young’s modulus, a thermal expansion coefficient that is preferably comparable to that of the substrate, a high yield stress, and a high creep strength. The thermal expansion coefficients of silver, gold, and copper are all insignificant. Silver and gold have the least yield stress of the three metals. Zinc and lead both have strong thermal expansion coefficients, and lead also has a low yield stress. Because metals with high electrical conductivity typically have low adhesion to substrates, neither silver nor copper has particularly good adhesion to ceramic substrates. To improve the adhesion property, intermediate layers of vanadium, chromium, or nickel might be utilized [50]. Copper and probably silver are the only metals with mechanical characteristics that are attractive.The substrate acts as a mechanical platform for the element as well as a heat conductor for the current-carrying conductive layer. As a result, superior thermal properties at ambient and working temperatures are preferred, but less favorable thermal properties at high temperatures are undesirable. This is because an increase in the thermal time constant speeds up the fuse action at high temperatures, which occurs in short-circuit situations. Excellent electrical insulation properties, a high melting point, good mechanical strength, good resistance to thermal shock, and relatively high surface smoothness have been considered to choose the substrate material. High surface smoothness is essential if the thickness of the conductive film is small. Polished alumina exhibits a small grain size and thus provides better surface smoothness. However, in other applications, such as electroless plating, a somewhat high surface roughness might be desirable since it allows for effective mechanical bonding. But depending on the prearching thermal absorption capability, alumina suits better as a substrate material.Gold films on alumina substrates were therefore selected for this investigation as the conductive film and substrate due to the fact considering that they had the fitted overall electro-thermo-mechanical properties. The details of the electro-thermal and mechanical properties have been listed in Table1. Thermally sensitive semiconductor resistors with a considerable reduction in resistance as temperature rises are known as the negative temperature coefficient of resistance (NTCR). When a current passes through the NTC resistance, however, it heats up due to power dissipation [51]. Resistance follows an exponential law in terms of temperature dependence. These resistors’ NTC feature makes them ideal for thermistors in temperature sensing and continuous overheat detection applications [52].Table 1
Electrical and Mechanical properties of different metals.
MaterialElectro-thermal propertyMechanical propertyElectrical resistivityThermal conductivityMelting pointThermal expansion coefficientYoung’s modulusYield stress10-8 ohms/mW/m° C°C10-6 °C-1GN/m2MN/m2Silver1.4742896119.182.729.4Copper1.5540310831713069-287Gold2.05319106314.178.529.4-39.2Aluminum2.523665923.570.635.3Zinc5.511742031104.5104Tin11.56823223.549.9N/ALead19.2363282916.14.9-9.8The resistance variation with temperature is measured using the temperature coefficient of resistance (TCR), dR/dT. The positive temperature coefficient of resistance (PTCR, dR/dT > 0) represents the increase in resistance as temperature rises, while the negative temperature coefficient of resistance (NTCR, dR/dT < 0) indicates the decrease in resistance as temperature goes up [53]. NTC resistors are made up of multivalent transition metal oxides like WO3, NiO, Mn3O4, Co3O4, Cu2O3, and Fe2O3, which produce a complex spinel (W, Mn, Co, Fe, Cu)3O4 structure for more dependable sensor applications [54]. NTC resistors perform because when the temperature rises, the number of active charge carriers released from the crystal lattice increases. The material for the NTC resistor is determined by several criteria, one of which is the temperature range demanded. Temperatures on the scale of 1 to 100 K are commonly employed with germanium NTC resistors [55]. NTC resistors made of silicon can withstand temperatures of up to 250 K. For the temperature range of 200 to 700 K, metallic-oxide NTC resistors are employed. Very stable compounds are still necessary at higher temperatures, and NTC resistors for these temperatures can be manufactured from materials such as WO3, Al2O3, BeO, MgO, ZrO2, Y2O3, and Dy2O3.To the best of our knowledge, this is the first work that shows a microfuse device that can control high currents using a transitional metal oxide as a heater resistor and a low melting point-based fuse element with analytical modeling and experimental fabrication. Temperature range, accuracy, stability, and specific electrical properties like current-time characteristics, voltage-current characteristics, and resistance-temperature characteristics are some of the parameters used to choose a material for an NTC characteristics-based heater resistor. Conductive polymer composite (CPC) material like carbon nanotubes (CNTs) in polyurethane (PU) foam has shown an NTC effect as the temperature rises from 25 to 100°C [56]. Transition metals such as Mn, Co, and Ni-based metal oxide Mn-Ni-Co-Cu-Si oxides with different compositions were fabricated, and it was found that the resistivity decreased exponentially with increasing temperature within the range of 25 to 85°C [57]. Thermistor based on ZnO and additives such as Sb2O3, Bi2O3, MnO2, Co2O3, and Cr2O3 make up a ceramic microstructure and exhibits NTC characteristics in the range of 400 to 750°C [58]. Tungsten oxide films exhibited a tendency for resistance decrease in the range of 30 to 450°C during gas sensor preparation and characterization using the screen printing method [59]. In another work, resistance decreases as temperature rises, suggesting semiconducting properties in the 100 to 450°C temperature range. This temperature range is well appropriate for the design of a microfuse using a low-melting-point- alloy material as the fuse material. Compared to other metal oxides, WO3 showed different crystal structures and thermal stability at different temperatures which makes it more promising and applicable for use as heater material, and also its temperature coefficient of resistance value exhibits a fitting model for the microfuse modeling and fabrication. This paper, for the very first time, has used tungsten oxide material for the heater resistor and also for the purpose of fabricating MEMS technology-based microfuse.WO3 is a transition metal oxide, and its lattice can withstand a considerable amount of oxygen deficiency, whereas WO3 oxygen additives can directly affect its electronic band structure and increase its conductivity by a large amount [60]. Depending on the stoichiometry, the electrical conductivity of single-crystal WO3 ranges from 10 to 10-4 Scm-1. As a result, the electrical characteristics of WO3 are highly influenced by synthesis techniques and growth environments, as stoichiometry and crystal phases depend on these processes [61].Chemical and physical deposition technologies such as electrospinning [62], spray pyrolysis [63], electrodeposition [64], thermal evaporation [65], plasma-aided evaporation [66], and DC and RF magnetron sputtering techniques [67] have all been utilized to fabricate WO3 films. Magnetron sputtering, for example, has the advantage of depositing uniform coatings on wide areas of substrates, a high degree of film adhesion, and relatively simple scalability properties. By using RF magnetron sputtering, the tungsten oxide films have been fabricated in low-temperature conditions.To create the protective fuse circuit, a metal must be manufactured in such a way that it melts when exposed to the heat of the heater resistance. A high-resistance and low-melting point-based alloy could meet that requirement of the fuse material. A tin-based alloy like 90Pb-10Sn has a melting point of 275 to 302°C (548 to 575 K). Low melting-point metals must meet certain requirements, including satisfying fuse qualities and ensuring enough insulating distance when the fuse alloy melts under excessive current and voltage [68].Normally, when current passes through a conducting path, heat is generated, and due to the heat dissipation, the designed fuse material melts. For a small amount of current flow, this fuse can be melted, and this interrupts the application of a thin film microfuse for high current and high-power applications. However, if any transitional negative temperature coefficient of resistance-based metal oxide is used between the conductor of the current and the fuse material that can perform a triode mechanism, the application of a thin film microfuse can be enhanced. If the self-heater resistance gets heated due to the electric current passing through the conducting path, and then it preserves a uniform temperature distribution during heating, then its total resistance would reflect its accurate temperature. In a normal rated current, the fuse will not be interrupted because of the self-heating heater resistance in the system. When overcurrent or abnormal current passes through the conducting path, then self-heater resistance shows its NTC characteristics, thus decreasing resistance with the increasing temperature, while raising the resistor’s temperature over that of its surroundings, increasing the conductivity through NTC material, and finally melting the fuse element, preventing the overcurrent from traveling through the conducting route.A microfuse fabricated by integrating Al/CuO-based nano energetic materials on a microwire was tested by an open-air combustion technique and also characterized [69]. A microcopper fuse on a glass epoxy plate was developed using wet etching technology, where numerical simulation was studied and fuse characteristics were evaluated experimentally [70]. A thin-film microfuse with a novel structure based on Ag deposition on the diarylethene (DAE) surface was proposed and characterized [71]. Here, an indigenously formulated lead-free thick-film NTC thermistor for self-heating applications was reported [72]. To get the complete static current-voltage characteristic of a thermistor, including the self-heating effect, an analog behavior model was presented as loaded and unloaded thermistors with NTC phenomena [51].A thin-film microfuse is thus necessary to control a high-rated current, and if overcurrent flows, then it should safely segregate the primary circuit from its source. To fabricate the fuse, the primary challenge is to make it compatible to control high current in a microfuse structure where the conducting film and NTC film thickness would be in the nanometer range. In literature, using a heating resistor in a microfuse structure cannot control high-rated current for large applications. To design a microfuse with high-rated current control capability, the NTC heater material has been proposed here. In this study, a thin film triode microfuse (5.4×3.2mm2) is designed, simulated, and investigated where the conducting film and heater thickness is 100 nm and 200 nm, respectively, which meets the criteria of a microfuse structure. An analytical analysis will be presented, and following that, the microfuse will be fabricated and tested, and the result will being shown and compared.


## 2. Modelling and Experimental

Thermally sensitive semiconductor resistors with a considerable reduction in resistance as temperature rises are known as the negative temperature coefficient of resistance. In some circumstances, the NTC element is considered as a fixed resistor, with 𝑅𝑇 varying with ambient temperature 𝑇𝐴.
(1)RT=RNexpβTA−βTN,where β is the material constant, and RN is the resistance at the nominal temperature TN (in K) [73].When a current passes through the NTC resistor, however, it heats up due to power dissipation. When an NTC resistor is placed in an electrical circuit, power is dissipated as heat, and the resistor’s body temperature rises above its surrounding ambient temperature. Energy must be supplied at a rate that determines the rate at which it is lost plus the rate at which it is absorbed (the energy storage capacity of the device) [74].
(2)dHdt=dHLdt+dHAdt.In an electrical circuit, the rate at which thermal energy is provided to the NTC resistor is equal to the power dissipated in the NTC resistor [75].
(3)dHdt=P=I2R=EI.The rate of thermal energy loss from the NTC resistor to the environment is proportional to the resistor’s temperature rise [76].
(4)dHLdt=δΔT=δT−TA.Here, (T) is the instantaneous temperature, andTA is the ambient temperature. The dissipation constant (δ) is defined as the ratio of a change in the power dissipation of an NTC resistor to the resulting body temperature change at a given ambient temperature. The dissipation constant is determined by the thermal conductivity, the relative motion of the medium in which the NTC resistor is placed, and heat transmission from the resistor to its surroundings via conduction through the leads, free convection in the medium, and radiation. Because it varies significantly with temperature and temperature rise, the dissipation constant is not a real constant. It’s usually measured in a state of equilibrium [77, 78]. The rate at which the NTC resistor absorbs thermal energy to cause a certain quantity of temperature rise can be represented as follows:
(5)dHAdt=smdTdt=CthdTdt,where (s) is the specific heat, and (m) is the NTC resistor’s mass. The heat capacity (Cth) of a resistor is the product of its specific heat and mass, and it is determined by the materials and structure of the NTC resistor [79]. As a result, the heat transfer equation for an NTC resistor at any point in time after power is provided to the circuit is as follows:
(6)P=dHdt=δT−TA+CthdTdt=VI.Here,dH/dt is the change of stored thermal energy with respect to time.We must analyze NTC resistor behavior under transient and steady-state situations to accomplish the analysis of the thermal characteristics of NTC resistors. When the power (P) is constant, the solution to Equation (6) is
(7)ΔT=T−TA=Pδ1−exp−δCt.Equation (7) demonstrates that an NTC resistor’s body temperature will rise above the ambient temperature as a function of time when a substantial amount of power is dissipated in it [80, 81]. By using this equation, we have designed the PSPICE analog behavioral model to understand the transient behavior of the NTC resistor.To understand and evaluate the NTC characteristics of WO3 metal oxide film, three samples of different thickness have been examined under temperature ranges from room temperature to 600 K. The relation between resistance and temperature has been plotted and shown in Figure 1. In this figure, we can observe that the two samples have shown similar characteristics of rapid decreasing of resistance with the increasing temperature until 320 K, and then it decreases very slowly with the increasing temperature. From this figure, the negative temperature coefficient of resistance of tungsten oxide metal oxide can be calculated.Figure 1
Negative temperature coefficient of resistance behavior of tungsten oxide.Figure2 represents the NTC resistor analog behavioral model (ABM) with the transient state characteristics using the PSPICE simulation package. In the figure, based on the detected current multiplied by the NTC resistance, E1 generates the voltage across the “NTC resistor” where V2 denotes an ambient temperature of 20°C. E3 symbolizes the changes in temperature or the temperature variation as a function of time which is the transient response or transient state of the system. Voltage source V1 worked to recognize the current, while V3 is necessary with R1 and R2 resistances to get the desired output.Figure 2
PSPICE ABM for NTCR with self-heating effect for transient response investigation.WhendT/dt=0 in Equation (6) or t>>C/δ in Equation (7), a state of equilibrium is achieved. The rate of heat loss is equal to the power provided to the NTC resistor in this steady-state situation. Therefore,
(8)δT−TA=δΔT=P=ETIT.Here, (ET) is the steady state or static NTC resistor voltage and (IT) is the steady-state current. The voltage-current characteristic is governed by this equation [82, 83].The heat transfer equation can be rewritten as follows when the power in an NTC resistor is reduced to a level where self-heating is regarded as negligible,(9)dTdt=−δCT−TA.This is simply Newton’s law of cooling [84, 85], and its solution is
(10)T=TA+TI−TAexp−tτ.In Equation (10), (TI) is the initial body temperature, (TA) is the ambient temperature, and τ is the thermal time constant of the device and τ=C/δ [86]. The thermal time constant is influenced by the same environmental elements as the dissipation constant, notably the NTC resistor’s size, shape, and leads, as well as the medium’s thermal conductivity and velocity, conduction via the leads, free convection in the medium, and radiation losses. To get the output of the circuit constructed in Figure 2, different dissipation factors have been considered to understand the transient state of the model. Figure 3 shows the output of the ABM circuit, showing the transient state of the NTC resistor temperature as a function of time. In this figure, NTC resistance is influenced by different dissipation factors of 0.5 mF to 1.5 mF, which validates equation (7). After getting the transient response of the NTCR, it is required to perform finite element modeling of four layers for the analytical assumption.Figure 3
Transient response of NTC heater resistor using an analog behavioral model.The major theme of this work is the analysis of the effects of the incoming current of the microfuse, the relationship between temperature vs. current, and voltage, and how much current is needed to melt the fuse material to fully protect the circuit from overcurrent. Here, for the first time, a WO3/Pb-Sn alloy-based microfuse structure on a gold electrode has been designed. Tungsten oxide film works as an NTC heater resistor, and Pb-Sn alloy is a low melting point-based fuse material. The COMSOL multiphysics platform is used to study conductivity and related features such as electric potential and the temperature profile.


## 3. Fundamental Device Design

This work mainly approached the modeling and optimization of different heater thicknesses, and different fuse alloy thicknesses and thus to find the amount of current required to reach the melting temperature of the fuse material. Figure4 shows the cross-sectional view of the triode microfuse. Figure 5 depicts a cross-sectional view with each layer identified by a different color, mentioning the melting point, boiling point, and density where Au, Sn, and WO3 will be fabricated using the nanofabrication technique.Figure 4
Schematic of a cross-sectional view of triode microfuse.Figure 5
Material layers used in the modeling of triode fuse (materials used to model the microfuse).To design the microfuse, different materials’ geometries are mentioned in Table2. The fuse material is selected based on the withstand capacity of the low-temperature melting mechanism. The total fuse geometry is 5.4×3.2 mm2 in length×width and 0.7 mm in thickness, as shown in Table 2. The properties of materials used in this analytical simulation are tabulated in Table 3. In this section, the design and simulation are performed based on these parameters. The structural design is shown in Figure 6. In Figures 6(a)–6(c), the conductive electrode (Au), heater (WO3), and fuse material (alloy) physical design have been shown. Figure 6(d) is the device’s appearance after declaring the material properties of Table 3, and Figure 6(e) displays the thermal environment which means a 25°C room temperature-based airbox is declared to assess the conduction, convection, and radiation effects using the heat transfer module of simulation on the device.Table 2
Dimension of the material for geometry of microfuse.
ParameterAlumina substrate (Al2O3)Gold (au) electrodeTungsten oxide (WO3) heaterTin (Sn)Lead-tin (Pb-Sn) fuseLength (mm)5.4—333Width (mm)3.2—12.42.4Thickness (mm)0.70.0010.0020.0010.1Table 3
Properties of material.
ParametersAl2O3AuWO3SnPb-SnYoung’s modulus (pa)3×10117.90×10107.40×10104.16×10102×1010Poisson ratio0.220.4150.490.330.43Density (kg/m3)3800193007160725010750Thermal conductivity (W/m-k)20.33101.6353.525Heat capacity at constant pressure (J/kg-k)880129315.34230140Electrical conductivity (S/m)1×10−1244.2×1062×1048.7×1064.76×106Figure 6
Design of triode microfuse structure. (a) Gold electrode on alumina substrate. (b) Tungsten oxide film on the gold electrode. (c) Pb-Sn alloy material on tungsten oxide and gold electrode. (d) Cross-sectional view of the device with material appearance. (e) Cross-sectional view of the device with the thermal environment.
(a)(b)(c)(d)(e)The analytical module on solid mechanics, electric currents, and heat transfer in solids is used to build the microfuse structure to achieve the desired findings that are available when using the finite element method approach. Normal meshes are configurable because active layers influence the shape and size of the mesh. Figure7 shows the three types of triode microfuse structures considered to simulate and investigate in this study. Figure 7(a) indicates the length and width ratio of the heater is 1 : 30, where Figures 7(b) and 7(c) show the length and width ratio of the heater is 1 : 20 and 1 : 10, respectively.Figure 7
Design of three different microfuse structures with different widths. (a) The length : width is 1 : 30. (b) The length : width is 1 : 20. (c) The length : width is 1 : 10.
(a)(b)(c)Figure8 depicts the top view of the 3D normal meshing for different heater ratios (1 : 30, 1 : 20, and 1 : 10) of the device from a cross-sectional view. In this simulation, 1 to 3 A of current is applied on the electrode of the microfuse with a step of 0.1 A current. The effects of applied current on potential, temperature, and resistance are quantitatively investigated. For the simulation of a microfuse, the joule heating and thermal expansion interface are studied where three major physics incorporates multiphysics effects such as solid mechanics, electric currents, and heat transfer in solids. The electromagnetic losses from the electric field as a heat source are added by the predetermined interaction.Figure 8
Normal meshing of the triode microfuse. (a) The length : width is 1 : 30 (b) The length : width is 1 : 20. (c) The length : width is 1 : 10. (d) Cross-sectional view of mesh analysis and (e) view of mesh analysis of the device with the standard thermal environment.
(a)(b)(c)(d)(e)


### 3.1. Solid Mechanics

The temperature of the heat transfer at the interface of the solid also acts as a thermal load on the solid mechanic’s interface, inducing thermal expansion. The solid mechanic’s interface is built on solving equations of motion in tandem with a solid material constitutive model. Displacements, stresses, and strains are computed as a resultant. Following the successful creation of the fuse device, it is necessary to combine it into a single device using the union function from a Boolean expression.


### 3.2. Electric Currents

To compute the electric field, current, and potential distribution in conducting electrodes, constant voltage and constant current have been employed. Both approaches yielded the same result: the resistance of WO3 reduced when the heating power was raised, and this can be explained based on Poisson’s equation,
(11)−∇2V=0.The physics interface uses the scalar electric potential as the dependent variable to solve a current conservation equation based on Ohm’s law.


### 3.3. Heat Transfer in Solids

The proposed device’s operating temperature transmits heat via heat conduction between the conductive electrode and the heater material layer, then raises the temperature by lowering the resistance, indicating NTC properties, and finally absorbs the heat as a self-heating mechanism. It melts the fuse material and instantaneously stops the current at the optimum temperature. The minus diagonal in temperature is precisely proportional to the temperature of the material we specified, according to Fourier’s rule, which is a principle that determines heat conduction is(12)q⟶n=−k∇T⟶.where k is the solid thermal conductivity, qn is flux density, and T is the device temperature. Then, the equation can be written as
(13)qn=−kidTdx+jdTdy+kdTdz.In then direction, we can write
(14)qnn=−k∇T⟶.So, the heat flux in all directions can be written as(15)qn=iqxn+iqyn+iqzn.


### 3.4. Boundary Condition

To successfully evaluate the simulation of the fuse device, the base of the microfuse and one corner of the fuse have been fixed under the module of the fixed constraint of solid mechanics. For electrical currents, the terminal and ground are declared as boundary conditions. And for heat transfer, the surrounding air was set to 293 K room temperature, and the terminal and ground parts were set to an initial temperature of 293 K. Electrical characteristics along with the side of temperature distribution because of applied current and voltage have been investigated thoroughly.


## 3.1. Solid Mechanics

The temperature of the heat transfer at the interface of the solid also acts as a thermal load on the solid mechanic’s interface, inducing thermal expansion. The solid mechanic’s interface is built on solving equations of motion in tandem with a solid material constitutive model. Displacements, stresses, and strains are computed as a resultant. Following the successful creation of the fuse device, it is necessary to combine it into a single device using the union function from a Boolean expression.


## 3.2. Electric Currents

To compute the electric field, current, and potential distribution in conducting electrodes, constant voltage and constant current have been employed. Both approaches yielded the same result: the resistance of WO3 reduced when the heating power was raised, and this can be explained based on Poisson’s equation,
(11)−∇2V=0.The physics interface uses the scalar electric potential as the dependent variable to solve a current conservation equation based on Ohm’s law.


## 3.3. Heat Transfer in Solids

The proposed device’s operating temperature transmits heat via heat conduction between the conductive electrode and the heater material layer, then raises the temperature by lowering the resistance, indicating NTC properties, and finally absorbs the heat as a self-heating mechanism. It melts the fuse material and instantaneously stops the current at the optimum temperature. The minus diagonal in temperature is precisely proportional to the temperature of the material we specified, according to Fourier’s rule, which is a principle that determines heat conduction is(12)q⟶n=−k∇T⟶.where k is the solid thermal conductivity, qn is flux density, and T is the device temperature. Then, the equation can be written as
(13)qn=−kidTdx+jdTdy+kdTdz.In then direction, we can write
(14)qnn=−k∇T⟶.So, the heat flux in all directions can be written as(15)qn=iqxn+iqyn+iqzn.


## 3.4. Boundary Condition

To successfully evaluate the simulation of the fuse device, the base of the microfuse and one corner of the fuse have been fixed under the module of the fixed constraint of solid mechanics. For electrical currents, the terminal and ground are declared as boundary conditions. And for heat transfer, the surrounding air was set to 293 K room temperature, and the terminal and ground parts were set to an initial temperature of 293 K. Electrical characteristics along with the side of temperature distribution because of applied current and voltage have been investigated thoroughly.


## 4. Simulation Results and Discussion

In this section, simulation results are presented to evaluate the performance of the proposed design. From the simulation, microfuse behavior in terms of temperature, potential, and isothermal contour distribution due to the applied current through a conductive electrode has been investigated. To examine the joule heating effect, different currents from 0.1 to 3 A were applied between the terminal and ground of the microfuse device, and the changes in temperature were observed. The current electrode has been used as a terminal and ground for applying the current flow in the device. At first, in the microfuse structure, we investigated the temperature distribution due to the applied current, and the result has been shown in Figure9. From this figure, we can see that the temperature increases with the increases in current applied, and the target temperature of nearly 600 K is reached in different applied currents. The length-to-width ratio of the triode microfuse device is related to this temperature distribution. In addition, from the figure, it can be estimated that the length and width ratio of the 1 : 30 sample shows the compatibility of controlling more current compared to the length and width ratios of 1 : 20 and 1 : 10. Besides, the length and width ratios of the 1 : 20 samples show better endurability compared to the 1 : 10 ratio sample. This shows the sample with the structure of 1 : 30 length and width ratio shows better fusing performance with a better current control mechanism as the temperature is mainly distributed throughout the channel created by the heater and electrode of the microfuse device. This result can also be supported by the results shown in Figure 10. Temperature versus applied current characteristics with respect to different triode microfuse structures have been shown in this figure. From the figure, it is evident that the sample with 1 : 30 ratio can control more current and power compared to the other two different structural microfuse devices.Figure 9
Temperature distribution of the triode microfuse device due to the applied current on the microfuse device. (a) The length : width is 1 : 30. (b) The length : width is 1 : 20. (c) The length : width is 1 : 10.
(a)(b)(c)Figure 10
Temperature vs. current characteristics of the microfuse device with different microfuse device structure.Next, we can also observe the isothermal temperature profile distribution of the three samples described in Figure11. Figure 11(a) shows the temperature distribution that is more supported to melt the fuse material of the microfuse device when the temperature reaches nearly 600 K. Figures 11(b) and 11(c) show the isothermal distribution is not uniform throughout the body of the microfuse device; hence, the melting mechanism can be interrupted due to this temperature distribution.Figure 11
Isothermal contour distribution due to electric current on the microfuse device. (a) The length : width is 1 : 30. (b) The length : width is 1 : 20. (c) The length : width is 1 : 10.
(a)(b)(c)Lastly, the voltage distribution due to the applied current in different microfuse device structures has been shown in Figure12. As can be seen from Figure 12(a), the voltage has been distributed throughout the electrode, which will enable the temperature distribution of the device to be more uniformly in the body of the microfuse. This result is agreed with the temperature distribution profile of the simulation and is more viable to be used as the design for fabrication in the laboratory.Figure 12
Voltage distribution of the triode microfuse device between current electrode due to the applied current on microfuse device. (a) The length : width is 1 : 30. (b) The length : width is 1 : 20. (c) The length : width is 1 : 10.
(a)(b)(c)


## 5. Testing Microfuse under Ambient Conditions

We used 2 separate modes to perform the joule heating effect experiment on the microfuse electrodes and heater resistor: constant current and constant voltage. Both techniques yielded the same result: as the heating power was raised, the heater material’s resistance decreased. The decrease in WO3 resistance with increasing heating power is due to the thermosensitive phenomenon discussed in the preceding section, in which increasing the temperature of the WO3 element increases its carrier concentration, hence improving its electrical conductance.It is crucial to address the contact between metals and semiconductor materials, i.e., the metal-semiconductor junction (MSJ), in order to realize the promise of MSJ-based devices for next-generation electronics. Contacts serve as a link between nanoscale MSJ-based materials and macroscopic applications, and they frequently dictate device performance [87, 88]. In MSJ-based devices, however, obtaining a low-resistance ohmic contact is difficult. In order to create an ideal ohmic contact in the MSJ, it is necessary to find a suitable combination of metal and semiconductor materials in which the semiconductor’s valence band maximum (VBM) is shallower than the metal’s work function (WF) (p-type MSJ) or the semiconductor’s conduction band minimum (CBM) is deeper than the metal’s WF (n-type MSJ), allowing the metal’s fermi level to lie within the bands rather than the gaps. As a result, forming an ideal ohmic contact with those MSJ-based materials is difficult for most commercially available 3D metals (with work functions ranging from 3.5 eV for Sc to 5.7 eV for Pt). An ohmic contact is crucial because it can passivate the electrical charge conduction in the conductor film of the microfuse device with a low resistance scheme [89, 90]. Thus, a low-resistance-based junction between metal and semiconductor (Au-WO3) provides a high-rated current configuration-based structure in the assembly [91–93]. Gating, surface doing, buffer layer, and metal work function engineering are some of the ways offered for constructing a quasi-ohmic contact or lowering the Schottky barrier height (USBH) [94].In Figure13, the cross-sectional diagram of four structures has been shown. For achieving low sheet resistance in the heater material, four different structures have been fabricated in the laboratory, and then the resistance has been measured using the low resistance measurement system of the Keithley SCS-4200 probe station. In Figure 14, the resistance and the contact type between the metal oxide semiconductor and metal have been portrayed. For structures (a) SiO2 substrate-WO3 heater-Au electrode, (c) SiO2 substrate-Al metal formation-WO3 heater-Au electrode, and (d) SiO2 substrate- Al metal formation-WO3 heater-Pt doping-Au electrode—the sheet resistance measured was very high and showed Schottky contact type behavior. Structure (b) SiO2 substrate-WO3 heater-Pt doping-Au electrode showed a high resistance of 13 KΩ which also denotes an ohmic contact type in the junction.Figure 13
Four types of device schematics for analyzing low sheet resistance in the tungsten oxide heater. (a) SiO2 substrate-WO3 heater-Au electrode. (b) SiO2 substrate-WO3 heater-Pt doping-Au electrode. (c) SiO2 substrate-Al metal formation-WO3 heater-Au electrode, (d) SiO2 substrate- Al metal formation-WO3 heater-Pt doping-Au electrode.
(a)(b)(c)(d)Figure 14
Four types of device structures are (a) SiO2 substrate-WO3 heater-Au electrode, (b) SiO2 substrate-WO3 heater-Pt doping-Au electrode, (c) SiO2 substrate-Al metal formation-WO3 heater-Au electrode, (d) SiO2 substrate- Al metal formation-WO3 heater-Pt doping-Au electrode, and their schematic, optical images, sheet resistance, and contact type between heater and electrode.As the resistance is quite high in the (b) SiO2 substrate-WO3 heater-Pt doping-Au electrode-based structure, a rapid thermal annealing process has been deployed to reduce the sheet resistance. With the characterization of sheet resistance, the property of the WO3 thin films is measured at various temperatures, and the effect of annealing on the transition temperature is studied. Current-voltage (I–V) measurements are performed to investigate the electrical conductivity properties of the heater material WO3 nanoparticle films before and after high-temperature annealing. Figure 15(a) shows the without annealed sample which shows nearly 13 KΩ sheet resistances, whereas Figure 15(b) shows that, in an argon gas atmosphere at 300°C with a 10-minute duration of the annealing process significantly decreases the sheet resistance up to nearly 2 KΩ. The annealing temperature was varied from 100 to 1000°C, and a different time range has been tested. During the testing, the temperature has been varied from room temperature to 150°C to get the variation, and with increasing temperature, the resistance decreased which also indicates the negative temperature coefficient-based characteristics of WO3 thin film.Figure 15
The current-voltage characteristics of the SiO2 substrate-WO3 heater-Pt doping-Au electrode device. (a) Without annealed condition and (b) 300°C for 10 minutes annealed condition of Argon gas atmosphere at WO3 nanoparticle film.
(a)(b)Figures16(a) and 16(b) support this negative temperature coefficient-based characteristic of WO3 thin film by plotting sheet resistance and temperature data without and with the annealing condition of the sample. Without annealed condition sample shows TCR=−0.30611°C−1, and a sudden drop out of the resistance from 13 KΩ to 11.7 KΩ has been noted when the temperature rises at 100°C. Figure 16(b) shows a TCR=−0.14583°C−1, and the resistance decreases slowly starting at 60°C.Figure 16
Temperature versus sheet resistance characteristics of the SiO2 substrate-WO3 heater-Pt doping-Au electrode device. (a) Without annealed condition and (b) 300°C for 10 minutes annealed condition of Argon gas atmosphere at WO3 nanoparticle film, and their corresponding TCR values.
(a)
Without annealed condition(b)
Annealed conditionA DC power supply has been used to provide constant voltage and current supply to test the microfuse, and the result is shown in Figure17. The voltage was fixed at 1 V, and the current of 0.33 A has been measured subsequently. Using an IR camera the maximum and minimum temperatures of the tested sample have been recorded which are 19.7°C. The total power calculated is 0.33 W. Then, applying a fixed voltage from 2 V, 2.5 V, 3 V, 3.5 V, and 4 V, the current was measured at 0.59 A, 0.74 A, 0.81 A, and 0.68 A, respectively, where the temperature was recorded at 80.6°C, 100°C, 130.1°C, 155.0°C, and 180.3°C. The maximum power consumed is 2.8 W, and after increasing the voltage from 4 V to 4.5 V, the fuse has been blown due to its melting temperature. This test has been performed repeatedly, and the result has been shown in Figure 18 by plotting current, voltage, and temperature with showing its breakdown point. Due to crack propagation and crack formation in the thin film layer and junction, the fuse has been blown before the estimated power has been applied. In the subset, a sample of the microfuse has been shown.Figure 17
Fixed voltage-current applied at the device during testing and their temperature has been recorded, respectively.
(a)(b)(c)(d)(e)(f)Figure 18
Current-voltage-temperature characteristics of microfuse device and fuse’s repeatability test with fixed current and voltage.Additionally, by correlating the results in Figures17 and 18, it is possible to develop the relationship between the temperature of the WO3 resistor when a certain power is applied. This is due to the fact that temperature rises locally at the WO3 resistor while the temperature at the WO3/Au junction remains relatively low. This result is also in solid agreement with the simulation result. Due to the low heat loss caused by the thermal conductance of the thin bridge, high temperatures are mainly concentrated at the WO3 resistor at the center part of the microfuse. Additionally, the temperature decreased significantly along the released bridge towards the fixed electrode pads. Therefore, the joule heating effect can elevate the temperature of the WO3 resistors and prevent the current from leaking through the substrate [95].For comparison with simulation data and also for controlling higher power and current, the fuse’s heater metal oxide film layer has been fabricated with more modifications. By changing the deposition time of the RF sputtering process, lower sheet resistance has been achieved (in this case, 45 minutes of deposition and annealing on the Pt surface). After following the Pt doping and annealing process, the sheet resistance of the newly fabricated sample has been shown in Figure19(a). For attaching the fuse element with the fabricated sample, a three-layer silver paste bridge has been used, as shown in Figure 19(b). In Figure 19(c), the blown fuse has been shown which showed the same phenomena as described in the simulation result. It may be inferred that this microfuse structure concept, which combines a fuse mechanism with a triode structure, can be used in a wide range of electrical, electronic, and industrial applications.Figure 19
After optimizing the heater material thickness. (a) Sheet resistance calculation. (b) Silver paste usage for the formation of bonding between the device and fuse material. (c) The fused/blown sample at optimum current (the middle black part has been blown).


## 6. Conclusion

In this current study, we designed a triode microfuse device that can be used as a protective device for a portable secondary battery like a high-rated current-based Li-ion battery from overcharging, which causes overvoltage and overcurrent as an application. Metal oxides that show the negative temperature coefficient of resistance characteristics are normally used as heater resistance, and in this study, we have used an NTC characteristics-based metal oxide, which is tungsten oxide, as a heater in our proposed microfuse structure that enables the advantages of safely flowing high current in a smaller fuse area compared to microfuse current rating, in other words, can control more electrical power. The transient behavior of NTC material has been modeled using PSPICE ABM, which makes it possible to simulate the transient behavior of temperature due to the Joule heating effect of the heater material, and the theoretical background suggests an analytical model to visualize the current conduction, heat transfer physics of the microfuse device. The analytical model has been validated by MEMS-based COMSOL Multiphysics, which provides the geometry of the device with the Joule heating Multiphysics platform. We proposed a complete device structure using the analytical model that combines the electric current and heat transfer module for the triode microfuse device. From the simulation, we found that the target temperature of melting the fuse material (Lead and Tin based alloy) can be reached with different geometrical structures, and the structure that shows the higher capacity to control more current and power has a more length-to-width ratio of the heater area. Simulation results demonstrated well the performance of the proposed model and the fabricated sample has shown nearly similar results experimentally. By fabricating different structures, the contact type has been fixed to ohmic contact for ensuring the performance as a microfuse in the junction of the metal and metal oxide semiconductor. The current, voltage, and temperature profile has been designed and the microfuse endures up to nearly 4 W power and 1 A current. For the secondary battery main protection fuse, this microfuse device permits current conduction safely by controlling high power compared to its size and shape. Also, a metal oxide like WO3 worked as a heater resistor with NTC characteristics for this microfuse device fabrication and that opens the door for analyzing the crystal structure and thermal properties of more transitional metal oxides in the future to get stable electrical and thermal characteristics. This microfuse device also provides an opportunity to fabricate this device at a low manufacturing cost due to the availability of fuse material alloy in bulk in the industry. The thin films used in this microfuse device have been fabricated by an RF magnetron sputtering system using the MEMS technology and this also has unfolded the opportunity of varying different fabrication parameters in designing high power controlled microfuse device. The current work advances the fusing mechanism, key materials, component configurational design, and fabrication method when compared to traditional fuse-device in terms of size and structure. The analytical model and finite element method of COMSOL Multiphysics in this work can be analyzed more for enabling more current control protection in upcoming works. Additionally, this study would encourage the creation of additional devices comprised of MEMS-based nanofabrication techniques, such as resettable relays or circuit breakers, logic switches, and resistance random access memory, to address some significant issues in future applications. The simulated result showed in this work predicted managing more high power in terms of high current control protection which we did not achieve exactly in the same figure in fabrication due to electrical and thermal stability and cracking phenomena which is also a motivation in the future study of this work. This microfuse can be applied to high power and high current-based applications and there are a lot of scopes to research more in the fabrication technique and controlling crack phenomena in the junction of electrode and heater resistor.



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*Source: 7525559-2023-03-13.xml*