End-of-Waste SiC-Based Flexible Substrates with Tunable Electrical

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End-of-waste SiC based flexible substrates with tunable electrical properties for electronics applications Anna De Girolamo Del Mauro, Sergio Galvagno, Giuseppe Nenna, Riccardo Miscioscia, Carla Minarini, and Sabrina Portofino Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b02716 • Publication Date (Web): 19 Sep 2016 Downloaded from http://pubs.acs.org on September 27, 2016

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End-of-waste SiC based flexible substrates with tunable

electrical

properties

for

electronics

applications Anna De Girolamo Del Mauro*, Sergio Galvagno, Giuseppe Nenna, Riccardo Miscioscia, Carla Minarini, Sabrina Portofino. ENEA, SSPT-PROMAS-NANO, Piazzale E. Fermi 1, 80055 Portici, Italy

ABSTRACT We demonstrated the suitability of polymer composites filled with Silicon Carbide (SiC) powders derived from a recycling process for applications in electronic devices manufacturing. SiC powders have been synthesized from process by-products and used as filler in the formulation of polystyrene/SiC composites which have been utilized in the preparation of substrates by solution casting. Different substrates have been prepared by changing the concentration of SiC in the composite in the range from 6.7 wt% to 67 wt% and utilized in simple electronic devices by performing gold contacts in both planar and stacked configurations. The electrical behaviors of both stacked and planar devices were investigated in direct current and alternate current regimes. The experimental results showed that charge percolation could be adopted as an explanation of the abrupt change in differential conductivity observed around 30wt%. Fowler-Nordheim tunneling at high fields has been found to be compatible with static

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characteristics and with high-frequency AC measurements and, therefore, charge tunneling between SiC islands has been proposed as the physical mechanism provoking the changes in charge transport in the investigated substrates. From this first experimental analysis, it appears that SiC/PS composites could suit the use in tunneling-gate dielectrics (i.e. in a transistors suitable for NVRAMs applications) for low concentrations, or as a continuous semiconducting media when SiC is dispersed in high concentrations composites.

KEYWORDS: silicon carbide, recycling, composite, charge transfer, material interfaces, impedance spectroscopy

1. INTRODUCTION In recent years, issues concerning a more efficient management of the resources, with particular emphasis on raw materials, gained a rising importance in the social, commercial and industrial policy of many countries; since this approach affects not only the environmental aspects but also the commercial strategy, concepts related to resources saving and circular economy started to be broadly shared and applied across the markets, promoting the introduction of reused, recovered and/or recycling-based products. In this frame, experiences related to the production of high added-value ceramics starting from end-of-wastes or waste derived product are exponentially growing, as many studies have demonstrated [1-4]. In particular, Silicon Carbide (SiC), a widely used non-oxide ceramic, has been usefully produced starting from biomasses and waste [5-8]. SiC is a material of great technological interest for its high hardness and strength, high wear resistance, low thermal expansion coefficient, excellent corrosion/oxidation resistance and good thermal conduction which make it widely used in


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microelectronics industry, especially in high power, high temperature and high frequency devices [9,10]. Due to its peculiar characteristics, SiC technology experimented a high boost, attracting developments in new devices formulation. Besides its consolidated utilization as a bulk material, SiC also starts to be experimented as a filler in polymer matrices in the preparation of composite materials with the aim to enhance or improve selected properties [1113]. Mavinakull et al. have prepared conductive SiC/Polypyrrole nanocomposites by oxidative polymerization and the effects of the nanoparticles loading and nanoparticle morphology (spheres and rods) on the physicochemical properties were investigated [14]. In our previous work, SiC powders from waste tires were already embedded in PMMAbased composites to explore their electronic applications leading to observe resistive switching effect in planar devices [15]. In this contribution, polymer composites having polystyrene (PS) as matrix and SiC from waste tires as filler were prepared by solution casting technique and used also as stand-alone substrates for electronic purposes. PS is often used as a polymer matrix as it allows the preparation of self-consistent substrates [16,17], able to host the direct realization of devices. In addition, when used as matrix, it may allow the use of the filler properties in order to formulate nanocomposites with enhanced technological properties, utilizable in many application field [18], especially with carbon-based materials [19-22]. The PS matrix is used together with Silicon Carbide (SiC) in a plethora of applications [23] because of its mechanical and chemical properties, high hardness, high wear resistance, low thermal expansion coefficient, good chemical resistance and good thermal conduction. Differently from plastic substrates which should not participate to the electrical operation of circuits and devices manufactured on the top of them, it will be shown that SiC-based


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composite layers can be electrically active and also they can be supposed to play the role of wafers in devices processing. Planar interdigitated and stacked contact geometries were performed on the prepared substrates in order to measure respectively resistive and capacitive characteristics. SiC percent concentration has been changed in order to study the electric characteristic of the composite in direct and alternate regimes. Charge percolation phenomenon was investigated and the role played by the organic/inorganic interfaces was considered [24]. To evaluate the transport and the dielectric properties of the composite, at different concentrations, impedance analyses were performed by means the UDR (Universal Dielectric Response) formalism [25]. In order to understand the boundary interfaces physics and the bulk properties in the devices under test, the tunneling and the hopping processes have been considered in the framework of the MillerAbrahams equation [26] to explain charge transport.

2. EXPERIMENTAL SECTION 2.1 Preparation of PS/SiC composites SiC powder was synthesized from tyre pyrolysis char and commercial and inexpensive silicon dioxide (Carlo ERBA silica gel 60 230-400 mesh ASTM), by means of a carbothermal reduction reaction [15, 27]. The obtained SiC was purified from the residual carbon by treating the samples at 700°C in oxidizing atmosphere and from the residual silica by dissolving the samples in hydrofluoric acid 50% in weight solution and by subsequently washing the residues with alcohol. Instead, the purification process from metallic impurities (like iron, zinc and chromium), which are present in waste derived materials, was conducted using chelating agents and basic solutions through a process able to drastically reduce the content of metals [28].


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A polymeric solution was prepared by dissolving PS in chloroform at a concentration of 5 wt% under stirring at 50°C. After completely dissolved, the solution was used as the starting batch: the final samples were prepared by adding different SiC powder amounts to portions of the polymeric solution and the dispersions were sonicated for 10 minutes in a ultrasonic bath at 100 W at ambient temperature. PS/SiC composite solutions were poured in a petri and filmssubstrates were obtained after the evaporation of chloroform solvent. After cast process, the films have different surface degree of finishing on each side: one side is more wrinkled and the other more smooth. The surface in contact with the petri appears smoother than the other one probably due to the fact that on this side, the composite is forced to follow the petri’s morphology during the casting. It was also observed that the substrates are less flexible at high SiC concentrations (>35 wt%). In the Table 1, the characteristics of the PS/SiC composites at different concentrations of SiC are reported.

TABLE 1 From Table 1, it is observed that the roughness on both side and the thickness of the films increases as concentration of SiC. 2.2 Devices preparation To manufacture the devices, Au-interdigitated contacts were evaporated on both side of PS/SiC substrates. As an example, the photo of a sample with 35 wt% SiC and the layout of the contacts of the substrates are shown in Figure 1. Geometry of contacts has been evaluated by imageprocessing 10x microscope data by calibrated software routines. FIGURE 1


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2.3 Characterizations The microstructure and chemical composition of the sintered samples were characterized by scanning electron microscopy (SEM, Model: LEO 1530). Phase identification of these samples was performed by the X-ray diffraction (XRD) method on an X'Pert MPD diffractometer using nickel filtered Cu K α radiation in the range of 2θ=20°-80° with a 0.050° step width and a 60 s counting time for each step. The devices obtained by depositing interdigital contacts on the “rough” and on the “smooth” surface of the PS/SiC composite films have been characterized by DC voltage scans performed by using a Keithley SCS4200 Semiconductor Characterization System equipped with preamplified source-measurement units. For each sweep, current-voltage steps have been performed with a hold time of 6s, a step delay time of 0.1s and voltage steps of 1V at ambient environment. Alternate current measurements, applying an amplitude voltage of 0.1 V, have been performed by using a HP 4192A impedance analyzer. The investigated frequency range was 102 ÷ 107 Hz.

3. RESULTS AND DISCUSSION Figure 2 shows the SEM characterization of the sample PS/SiC (67 wt%) obtained by casting. The analysis reveals that the average size of particles is below one micron. It has also to be remarked that there is an appreciable quantity of SiC fibers randomly deposited (Figure 2a) which are formed via gas-gas reactions between SiO (g) and CO (g) as follows [29]: SiO(g) + 3CO(g) → SiC(s) + 2CO2(g)

(1)

3SiO(g) + CO(g) → SiC(s) + 2SiO2(s)

(2) FIGURE 2


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As it has been already mentioned, it has been possible to discriminate two kind of surfaces: one’s wrinkled (2a) and the other one’s smooth (2c). At higher magnifications, Figure 2b reveals a uniform coverage of PS with SiC particles. The flat side of the sample (Figure 2c) has a quite different morphology: in this case, it can mainly be seen the surface of PS with holes in which SiC islands are evident. From the cross-section of the film-substrate, the two surfaces are better shown and in particular in the wrinkled surface it is observed that the SiC is uniformly dispersed into the polymer matrix (Figure 2d). The incorporation of SiC in PS matrix was confirmed by XRD analysis (Fig. 3). The XRD pattern of the SiC shows sharp and well defined peaks indicating the crystalline nature of SiC and the observed 2θ values are consistent with the standard JCPDS values (JCPDS No. 29– 1129). The strong peaks at 2θ = 35.7°, 41.4°, 60.0°, and 71.8º, corresponding to 111, 200, 220, 311 lattice planes can be attributed both to α and β phases of SiC, respectively [30-32]. Relatively weak peaks are present at 2θ =33.7° and 38.1° and could be due to the α-SiC. Figure 3 (insert) shows that PS exhibits a single broad diffraction peak at 2θ values around 20°, indicating the amorphous structure of the polymer. When SiC particles are incorporated into PS matrix, the XRD patterns of PS/SiC composites are very similar to that of SiC and only the diffraction peak of the PS is more intense at high concentration of SiC. FIGURE 3 To analyze the electrical properties of the composite and its interfaces with the gold contacts, static I-V measurements in direct current and alternating current were made (see Figure S1 in Supporting Information). Because of the non-linearity of the electrical characteristics, a comparison between the samples could be performed straightforwardly by considering the zerobias differential conductance (Gd0) as defined by eq. 3:


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≡ 0 ≡

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(3)

being IF the current flowing through the device, V the bias voltage, Gd the differential conductance and Gd0 its value at V=0V bias. By extracting Gd0 for each device, the static behavior of the PS/SiC films has been compared at small bias values when changing the SiC content percentage in the composite and the contact surface; the extrapolated data are reported in Figure 4. FIGURE 4 From the plots of Figure 4, it can be deduced that Gd0 increases as the SiC concentration increases. For small concentrations of SiC (below 30%), flat surfaces result in a more conductive device respect to the rough one. Such difference increases as the SiC concentration decreases. In other words, the interface effects have been found to be more evident for low conductance composites. It can also be observed that Gd0 shows a critical threshold for concentration near 30%wt. Above this value, Gd0 rises abruptly of five orders of magnitude to a high-conductance limit having less dependence from the adopted contacts surface (rough or flat). From this observations, we can hypothesize that in composites having SiC concentration from 6.7 wt% to 30 wt%, the space between the SiC grains becomes smaller as the SiC wt% increases and some conduction pathways begin to form, therefore Gd0 increases with wt%. When the concentration overcomes the 30% limit, many SiC conduction paths are fully formed therefore, a further increase of the SiC content does not significantly increase Gd0 and then we assist to a saturation behavior.


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Summarizing, in the high concentration regime (>30 wt%) the charge transport in SiC grains dominates while in the low concentration regime the interstitial PS acts as a current limiting agent both in the bulk and in the contact interfaces. This explanation falls in the framework of studies on the percolation limit in polymer-based dispersions of conducting materials [33] and in field-effect devices fabricated by utilizing inhomogeneous materials [34] which have been employed in the interpretation of electrical data as a function of the volume fraction of a filler in a PS matrix [35,36]. As it has previously observed, charge conduction has been found to be dependent from the substrate interface finishing, therefore, in order to understand the effects bound to buried and boundary interfaces in the analyzed devices, the Fowler-Nordheim (F-N) [37,38] model has been adopted. The model describes the physical behavior of electrical currents coming from the extraction of charge by the means of a tunneling process through a triangular barrier promoted by the electric field. This approach applies to the high-fields regime, in absence of heating, where charge carriers that do not have enough energy to overcome the barrier can pass through by tunneling. In its simplest form, the F-N model gives the current (I) - voltage (V) characteristic of a device according to eq. 4.

=

∙ ∙

(4)

where A’FN and B’FN are the F-N coefficients. In our case, the device’s structure is symmetric (Au/composite/Au), therefore its I-V curve should be symmetric in turn. Because of the nature of the composite and the physical structure of the device, the potential barrier should be attributed to a thin layer of PS which separates the gold


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electrodes from the SiC semiconductor (boundary interface) or two grains in the bulk (bulk interface). In the latter case, tunneling processes should happen between SiC islands interleaved by PS interstitial zones. By adopting the model in eq.4 for the flat-surface devices in the regime of high voltages, a field-emission regime has been identified for high bias voltages where the model in eq.4 fits experimental data. The field-emission regime is the voltage range of validity of the Fowler-Nordheim model. In this range, the emission of electric charges from an electrode is promoted by the electric field. In detail, the Fowler-Nordheim plots (F-N) are reported in Figure 5. FIGURE 5 As it can be stated from Fig. 5, the F-N model can be applied easily for low values of 1/V (highvoltage regime) for the 6.7, 20 and 25 wt% samples. As the SiC concentration increases, zoomed plots have to be considered to identify the field-emission regime, as in the case of 35 wt% and 67 wt% samples (see Figure S2 in Supporting Information). From the slope of the F-N plots, it is possible to extract the term B’FN which is bound to the barrier energy. B’FN can be explicated according to the eq. 5: =

∗ "# $%&

(5)

where q is the electron charge, m* is the carrier’s effective mass in the transport material, d the barrier width and φ the barrier height which is bound to material’s physical properties at the interface [39]. The extracted data are summarized in Figure 6. FIGURE 6 It can be seen that for higher concentrations of SiC, the B’FN value gets lower and approaches to 0V. Vice versa, at low SiC concentrations, high B’FN barriers are possible because the barrier


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increases width “d”. Therefore, we can assume that by increasing the SiC concentration in the composite, the barrier width (bound to the distance between the injecting surface and the transport material) decreases and becomes nearly null for concentrations higher than 30-35wt%. The percolation limit in the bulk, and barrier nulling in F-N analyses seem to be ruled by the same concentration threshold. In other words, from these observations, it is possible to suggest that it exists a threshold in SiC concentration that has to be overcome in order to switch off the F-N barrier in the device. It can be noticed from Figure 6 that B’FN decreases linearly with concentration below 35wt%. At 67 wt% concentration, it is likely that the linear behavior is not obeyed because the SiC islands get in contact forming continuous conducting pathways, therefore the barrier disappears and B’FN approaches to zero. On the other hand, A’FN is related to the semiconductor conductance: in fact it increases with the concentration up to a saturation regime, as shown in Figure 6. In this case, it is possible to hypothesize that a greater amount of SiC islands offers a superior conduction cross-section to the current density then the increase in A’FN. By comparing data obtained from rough and flat surface devices in terms of F-N barriers, we can observe from Figure S3 in the Supporting Information that below the concentration threshold (< 35wt%) both types of devices show a decrease in barrier width with the increase of SiC concentration. Furthermore, it appears that devices having the contacts deposited on the top of the rough surface have typically higher B’FN barrier values than the ones contacted on the top of the flat surface. This can lead to hypothesize that the F-N tunneling has to be also a property of the gold contact/composite interface and not just of SiC-SiC tunneling process through PS, as it will be shown in the next part of the article. In this case, the field-emission phenomenon should


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be associated to the interaction between the contacts and the composite. In this framework it can be stated that the higher the SiC concentration, the higher the injection rate at the contacts interface. Finally, it can be suggested that in the case of concentrations under 20 wt%, the rough surface is not characterized by enough thin gaps affected by field emission. In the opposite case, for concentrations of 67 wt%, there is a significant part of SiC islands shorting with the gold contacts making the barrier difficult to be evaluated. To deeply analyze the electrical behavior of the composite, capacitors have been manufactured in a stacked configuration in order to evaluate the transport and the dielectric properties of the composite. In literature many papers deal with the dielectric properties of amorphous materials by adopting the impedance spectroscopy as a tool to comprehend their electrical properties [4043]. The capacitors were made using part of the same substrate employed to realize the planar devices and depositing gold on both sides of the substrate itself (on either the wrinkled and smooth part). The gold contacts have been evaporated in form of strips having a width of 3 mm and the active area, which is associated to the crossing of the two strips, is 9 mm2. In this case, the device with 20 wt% and not the one with the 25 wt% has been analyzed because their behavior is quite similar and would not add any essential information. In this analysis, capacitance and conductance as a function of frequency for the different fabricated devices are shown in figure 7. The device with SiC 6.7 wt% showed a capacitive trend as an insulator while in the conductance trend the device with 67 wt% could be considered a doped semiconductor. FIGURE 7 The frequency dependence of conductance in the log-log plot of Figure 7b suggests that, at high frequencies, experimental data can be fitted by the UDR model [25, 42, 44], which for G predicts the expression (see in particular the dash line):


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' = + ) ∗ ' *

(6)

where G0 represents the DC conductivity and AG is the constant phase element showing both the dispersion of conductivity and the dielectric properties of the filling material [45]. The origin of eq.6 lies in the intimate character of many-body interactions occurring among the inorganicorganic material basic constituents, which lead to a cooperative relaxation of polarisable entities rather than an independent behavior for them under the effect of a varying field. In this case, the G0 parameter (Figure 8a) seems to follow the trend already observed in the DC measurements (see Figure 4), with a saturation behavior for high concentrations. Near the percolation threshold, not completely saturated

paths generally allow also, especially in a

frequency abnormal accumulation of charge within the composite. In particular metal-insulator composites [46-47] could realize networks that can lead to a, so called, giant capacitance which, in our case, undergoes to a jump of more than one order of magnitude. FIGURE 8 Typically, the exponent “s”, in equation 6, allows to classify the electrical nature of the investigated amorphous materials: “s” was experimentally demonstrated to be close to 0.6-0.8 [37] or to 1 [43] for amorphous semiconductors and insulators, respectively. In this case, the s parameter changes from 0.8 to 0.4 as the SiC concentration increases, going further down the already mentioned typical semiconductor values (figure 8b). This probably happens because we were not able to remove, from the plot, the contribution of the series resistance of the capacitor, since we could not reach a saturation conductance regime with the utilized range of frequencies, underestimating the s parameter. Moreover our material behaves like a doped semiconductor due, probably, to the aluminium presence in the used precursor.


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In disordered systems, without long range order, as it could be in an amorphous/organic semiconductor, the carriers are localized on different grain/molecular sites and charge transport usually arises as a hopping process. In this way we can explain the Figure 8b where the AG parameter increases exponentially without reaching any saturation regime. In order to account this behaviour, we can consider that the hopping transport takes place through tunnelling transitions between localized states. The transition (jump) probability is given by the MillerAbrahams (M-A) equation [26, 48, 49]: ν,- = ν exp 1−

345 6

exp −

94 95

for E@ < EB :; 78 1 for E@ > EB

(7)

where ν0 is the attempt to jump frequency, Rij is the hopping distance, α is the localization length, while Ei and Ej are respectively the energy of the initial and final energy states in the jump. The first term depends from the distance between two jumping sites (particle-particle or electrode-particle) and is strictly related to the AG term. For the sake of completeness, we have to consider also the distance between the contacts and the first particles (boundary particles), but in the AC regime it acts like the distance between particles itself because when the signal change sign also the injecting contact will change and the device acts as it were folded on itself, similarly to a torus shape. So Rij is the distance between the particles and it is linearly dependent from the wt% and AG extrapolates and predicts with very good approximation the bulk behaviour from the electric point of view. Moreover, in our case we can assume constant the second term in the M-A equation because all the measurements have been performed at the same temperature and with the same bias conditions. In Figure 9 the carrier thermal activation energy is extracted for the film at 67 wt% for both kind of interface (smooth and rough). We chose to study the device with 67 wt%


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because it is the one in which the current is expected to change more drastically as a function of temperature. In the picture it is evident that the thermal activation energy depends on the finishing of the interface. Then we expect that, at low field regimes (Bias = 1 V), the second term of the Miller-Abrahams equation could be related to the bulk but also to the nature of the contacts (see figure 9), although in our case the contribution related to the variation of the temperature can be considered as a constant because the DC and AC measurements were performed at room temperature. FIGURE 9 Then on the basis of DC and AC analyses, also considering the differences between the low and high fields regimes, we can summarize the conductance dependence from bias, frequency and temperature as in the equation 8: GV,ω,T = 0

4KL2N∗ O3 3%Q −

+ AνS exp 1−

345 6

exp −

94 95

for E@ < EB :; 7ω 8 1 for E@ > EB *

(8)

In particular both d and Rij depend from the particles concentrations of the composite. From equation 8 it is easily possible to describe the regimes already observed. At high fields and low frequencies the F-N regime will dominate, while in the low bias and high frequency regime the M-A rules the conduction and also describes thermal effects. In this way we could explain the attempts of some works to introduce the temperature dependence of the field emission mechanisms [50-53]. Therefore we have made a detailed study about the electrical properties of the SiC/PS composite by means of F-N tunneling, the UDR and the Miller-Abrahams theories. Putting together all these formalisms in an unconventional way to explain the electrical behavior of this specific composite. Probably this kind of approach can be extended to other types of composites giving a


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new reading to their electrical properties, going to separate the various contributions and going to study the doping material in a more detailed way. By considering the reported analyses, we can conclude that the wt % in the SiC/PS composites can be utilized to tune the properties of the material, making in turn to be suitable as a tunneling gate dielectric in a FET structure for flash-memories (low concentrations) or as a continuous film for high concentrations in applications requiring a semiconductor layer. By means of the UDR formalism and the Miller-Abrahams equation, we could decouple the contribute due to the bulk of the device from the contribute due to the electrical contacts. In particular, from the AG vs wt% plot it is possible to extrapolate and predict with very good approximation the bulk behaviour from the electrical point of view excluding the contribution due to the electrical contacts. In the future, it would be interesting to develop a theory to study the links between the parameter AG and the second term of the Miller-Abrahams law in order to analyse charge transport in nanocomposites constituted by an insulating matrix and filled by, semiconductors, doped semiconductors, conductors, etc..

CONCLUSIONS In this work, polymer composites with PS as matrix and SiC as fillers were prepared by solution casting technique and used as substrates/devices for electronic applications. Planar Auinterdigitated devices and stacked capacitor devices were realized at different SiC wt% to study the electric characteristic of the composite in direct and alternate regimes. We were able to identify the wt% to activate the percolation regime and to relate the conductivity threshold to modifications in the average barrier width in a field-emission model.


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The device behavior at high frequencies, in AC regime, confirms the abstractions about simple tunnelling mechanism already adopted ad high fields, in static regimes, by means of the FowlerNordheim law. In particular, by using the UDR formalism and the Miller-Abrahams equation we were able to resolve the contribute due to the bulk of the composite from that due to the electrical contacts. Concluding, it is possible to manipulate the electrical behaviour of the device by changing the wt% concentration in the SiC/PS composite. Moreover, because of its tunable properties, we could envision application for this composite in tunneling dielectrics for flash memories, or as a continuous film in applications requiring a continuous semiconductor layer (for high SiC concentrations). Device architectures combining stepped or gradually changing SiC wt% are also possible in order to take advantage from both types of composites. It is also noteworthy to observe that the reported results clearly point out the use of waste processing treatments as a source of materials for applications in electronic devices manufacturing.

ACKNOWLEDGMENT The authors are grateful to Dr. Carmela Borriello for her assistance in XRD measurements. This work has been supported by the Italian Ministry of Education, University and Research (MIUR) through the National Project entitled SMARTAGS (PON02_00556_3420580).

AUTHOR INFORMATION Corresponding Author *Anna De Girolamo Del Mauro, [email protected], +39 081 7723389


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Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ‡These authors contributed equally.


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CAPTIONS Table 1. Characteristics of the PS/SiC samples prepared via solvent casting method Figure 1. Photo of device with 35 wt% SiC and the characteristics of contacts geometry realized Figure 2. SEM pictures of PS/SiC (SiC 67wt%) casting composite-substrate: (a) rough surface, (b) higher magnification of (a) ,(c) flat surface and (d) cross-section. Figure 3. X-ray diffraction patterns of (a) sintered SiC and PS composites with SiC (b) 6.7 wt%, (c) 20 wt%, (d) 25 wt%, (e) 35 wt%, (f) 67 wt% and (g) pure PS Figure 4. Zero-bias differential static conductance versus SiC concentration in composites Figure 5. F-N plots of Au/composite/Au planar devices built on the top of the flat surface Figure 6. B’FN and A’FN plotted against SiC concentration Figure 7. (a) Capacitance and (b) Conductance as a function of frequency for the different capacitors fabricated Figure 8. (a) Static conductance G0, (b) the S slope and (c) the AG intercept in the UDR model in function of SiC wt%. Figure 9: Arrhenius plot of the device current versus 1/T for the highest concentration sample.


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Fig.1


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Fig.2


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Fig.3


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Fig.4


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Fig.5


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Fig.6


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Fig.7


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Fig.8


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Fig.9


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Samples 1 2 3 4 5

Concentrations Roughness Rq (µm) SiC in PS (wt%) Rough Side Flat Side 6.7 0.094 0.087 20 0.323 0.103 25 0.583 0.196 35 4.7 0.131 67 11.1 1.5

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Thickness (µm) 140 160 190 220 310

Table 1


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GRAPHICAL ABSTRACT


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End-of-Waste SiC-Based Flexible Substrates with Tunable Electrical

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