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    • 专利摘要:
    A diode comprising a first and a second electrode; a semiconducting layer comprising semiconducting particles at least partly embedded in a mixture of glycerol and cellulose based material, wherein said cellulose based material is nano-fibrillated cellulose (NFC); wherein said first and second electrodes and said semiconductor layer are at least partially stacked on top of each other in a first direction; wherein the amount of glycerol present in the semiconducting layer is in the range of 5 wt% to 75 wt%, and the amount of nano-fibrillated cellulose (NFC) present in the semiconducting layer is in the range of 10 wt % to 50 wt%; as well as a method of producing the same.
    公开号:SE1650220A1
    申请号:SE1650220
    申请日:2016-02-19
    公开日:2017-08-20
    发明作者:Andersson-Ersman Peter；Wang Xin；Dyreklev Peter；Gustafsson Göran；Berggren Magnus；Crispin Xavier；Abdollahi Sani Negar；Engquist Isak；Granberg Hjalmar
    申请人:Acreo Swedish Ict Ab；
    IPC主号:
    专利说明:

    DIODE AND METHOD FOR PRODUCING THE SAME Technical field of the lnvention The present inventive concept relates to the field of diodes, and moreparticular to diodes which can be manufactured from solution processing.
    Backqround of the lnvention Flexible electronics, i.e. electronics printed on flexible or bendablesheets have been developed since 1960s. Today, when not only people butalso things are becoming connected to Internet, the demand for flexibleelectronic components is driven by a vast array of distributed applications,such as wearable electronics, e-labels and point-of-care sensors. These willserve as outposts of the Internet of Things (loT), and to power up andcommunicate with all the e-tags a wireless energy harvesting technology thatoperates at high frequencies is needed. A rectifier in combination with anantenna is a viable solution for this, wherein a single diode can serve as therectifier. Diodes are also widely used in AC/DC converters, signal transmittersand receivers, voltage regulators, etc. The diode is therefore a key-enablingcomponent for loT solutions based on flexible electronics powered by, andcommunicating via, radio frequency electromagnetic fields. One way toachieve flexible circuits is to use printing methods in order to manufacture thinfilm devices on foils.
    Sani et al. (All-printed diode operating at 1.6 GHz; PNAS, 2014, 111,11943-11948) described that this technique could be used for diodesoperating at the Ultra-high-frequency (UHF) band.
    However, there is a need for diodes that may be manufactured bysolution processing, and which have a lower threshold voltage, a higherrectification ratio and/or higher current density.
    Summary of the lnvention ln view of the above-mentioned and other drawbacks of the priorart, a general object of the present invention is to improve the current state ofthe art and to mitigate at least one of the above mentioned problems. This and other objects are achieved by a diode with a lower threshold voltage, ahigher rectification ratio and/or higher current density.
    According to at least a first aspect of the present invention, a diode isprovided. The diode comprises: - a first and a second electrode; - a semiconducting layer comprising semiconducting particles atleast partly embedded in a mixture of glycerol and cellulosebased material, wherein said cellulose based material is nano-fibrillated cellulose (NFC); wherein said first and second electrodes and said semiconductor layer are atleast partially stacked on top of each other in a first direction; wherein the amount ofglycerol present in the semiconducting layer is in therange of 5 wt% to 80 wt%, and the amount of nano-fibrillated cellulose (NFC)present in the semiconducting layer is in the range of 10 wt % to 50 wt%.
    Besides meeting the above object, the invention is also advantageousin that it provides a diode that may be produced using fewer materials so thediode is favorable from a production and an environmental point of view.Further, it may be produced by solution processing by means of casting andlamination, so it provides a simplified manufacturing process. Additionally oralternatively, it may provide an improved manufacturing yield.
    According to literature the term nanocellulose means nano-structuredcellulose. ln nanocrystalline cellulose (NCC), the amorphous parts of thenanocellulose have been chemically removed, and in bacterial nanocellulosethe nano-structured cellulose has been produced by bacteria. Further,“fibrillated nanocellulose” means that the cellulose fibers have been fibrillatedto achieve agglomerates of cellulose microfibril units. Such “fibrillatednanocellulose” is sometimes called cellulose nanofibrils (CNF), sometimescalled microfibrillated cellulose (MFC), and sometimes called nanofibrillatedcellulose (NFC); and these terms are used interchangeably in literature.Throughout this application the term nanofibrillated cellulose (NFC) is used 3 when referring to “fibrillated nanoce|u|ose”, i.e. nanocellulose that has beenfibrillated. “Fibrillated nanoce|u|ose”, or nanofibrillated cellulose (NFC), maybe derived from wood and has nanoscale (less than 100 nm) diameter andtypical length of several micrometers, but may also be shorter. Moreinformation may be found in K. Missoum et. al. “Nanofibrillated CelluloseSurface Modification: A Review.” Materials 2013, 6(5), 1745-1766(doi:10.3390/ma6051745).
    According to at least one embodiment of the invention the semi-conductive material, the cellulose based material and the glycerol may bemixed to a mixture, e.g. a homogenous mixture, where the semi-conductingmaterial contributes to the conducting layer being electronically conductingand/or semiconducting. lt should be understood that in the context of thisapplication, the term ”homogenous” means a composition where allcomponents present in said composition have been well blended with eachother and are not present in the form of layers. As the components of thecomposition have differing sizes and structures it is not possible to achieve amixture which is identical throughout every single miniscule portion, and thushomogenous is not to be interpreted in this way. According to at least oneembodiment of the invention, the composition should be well mixed with avariance throughout the composition between the components of thecomposition not exceeding a 20% difference in the concentration of each ofthe constituents when comparing two different samples taken from the samecomposition, preferably said variance should not exceed 10% difference.
    Optionally, the electronic conductivity of the semiconducting layer islarger than 1E-5 S/cm, or larger than 1E-4 S/cm, or larger than 1E-3 S/cm.
    Optionally, the ionic conductivity of the semiconducting layer is lowerthan 1E-4 S/cm, or lower than 1E-5 S/cm, or lower than 1E-6 S/cm.
    According to at least one embodiment of the invention the amount ofglycerol present in the semiconducting layer is in the range of 5 wt% to 80wt%, or 10 wt% to 75 wt%, or 15 wt% to 70 wt%, or 25 wt% to 60 wt%. 4 According to at least one embodiment of the invention the amount ofnano-fibrillated cellulose (NFC) present in the semiconducting layer is in therange of 10 wt% to 50 wt%, or 15 wt% to 45 wt%, or 25 wt% to 40 wt%.
    According to at least one embodiment of the invention the amount ofsemiconducting particles present in the semiconducting layer is in the rangeof 0.1 wt% to 85 wt%, or 1 wt% to 60 wt%, or 5 wt% to 30 wt%, or 10 wt% to20 wt%. Additionally or alternatively the amount of semiconducting particlespresent in the semiconducting layer is at least 0.1 wt%, or at least 1 wt%, orat least 5 wt%, or at least 10 wt%, or at least 20 wt%, or at least 30 wt%, or atleast 40 wt%, or at least 50 wt%, or at least 60 wt% or at least 70 wt% or atleast 80 wt%, or at least 90 wt% or at least 95 wt%. Additionally oralternatively the amount of semiconducting particles present in thesemiconducting layer is lower than 1 wt%, or lower than 5 wt%, or lower than10 wt%, or lower than 20 wt%, or lower than 30 wt%, or lower than 40 wt%, orlower than 50 wt%, or lower than 60 wt%, or lower than 70 wt%, or lower than80 wt%, or lower than 90 wt% or lower than 95 wt%.
    According to at least one embodiment of the invention the glycerol, thecellulose based material and the semiconducting particles constitute 75 wt%,or 85 wt%, or 95 wt% of the semiconducting layer.
    According to at least one embodiment of the present invention thesemiconducting layer is self-adhesive. The glycerol makes one, two or allsurfaces of the semi-conducting layer self-adhesive. lt should be understoodthat in the context of this application, the term 'a layer being inherently self-adhesive' means that when the layer is split in two, the thus exposed surfacesare also self-adhesive. The self-adhesive properties of the layer may be atleast partly attributed to the hygroscopic properties of glycerol. lt shouldfurther be understood that the said self-supporting semiconductive layer maybe attached and/or detached from said surface and/or said electrical surfaceusing its self-adhesive properties. That is, by being self-adhesive, said self-supporting semiconductive layer may be attached and/or detached from saidsurface and/or said electrical surface in an easy manner. 5 According to at least one example embodiment, said semiconductinglayer may be attached to a first position/surface, e.g. an active or a non-activeposition/surface, and then detached from said first position/surface, andattached to a second position/surface being an active position/surfacedifferent from said first position/surface, e.g. when the user wants to activateor change the functionality of the semiconducting layer.
    According to at least one example embodiment of the invention thesemiconducting layer is self-supported. lt should be understood that thewording “self-supported” is indicating that the layer may be manufacturedand/or held without the presence of a substrate or carrier, such as a PET-foil.The self-supporting properties of the layer may be at least partly, or fully,attributed/assigned to the use of a nano-fibrillated cellulose and/or micro-fibrillated cellulose in the self-supporting layer. Thus, the the nano-fibrillatedcellulose and/or micro-fibrillated cellulose at least partly contributes to theself-supporting properties of the self-supporting layer. The self-supportinglayer may preferably be flexible and/or elastic.
    Since the semi-conducting layer according to one exampleembodiment can be both a self-supported semi-conductive layer and a self-adhesive semi-conducting layer, it can also be referred to as a self-supporting, self-adhesive semi-conductive layer.
    Hence, according to at least one embodiment of the invention thesemiconducting layer includes further material improving the diode. Suchmaterials may according to at least one example embodiment be pigments.
    According to at least one example embodiment, said diode comprisesa protective layer, to protect from impurities/particulates and/or evaporation.Optionally, the protective layer is self-adhesive.
    According to at least one example embodiment of the invention thesemiconducting particles forms a single layer in said semiconducting layerwhere single semiconducting particles are in contact with both the bottom andthe top electrode. ln other words, the single layer of semiconducting particlesmay dominate the charge transport property. lt should be understood that the single layer is arranged at least where the two electrode overlap each other in 6 the vertical direction. When the particles are arranged in such a single layer amajority of the semiconducting particles may be in direct contact with both thefirst and the second electrode, but there are also other configurations ofsingle layers.
    Hence, the particles being in contact with both the first and the secondelectrode constitute the thickness of the semiconducting layer.
    According to at least one example embodiment of the invention thesize of the semi-conducting particles are larger than 5 pm in at least a firstdirection; and/or the size of the semi-conducting particles is less than 100 pmin at least said first direction, or less than 50 pm in at least said first direction.
    According to at least one example embodiment the semi-conductingmaterial is provided in a particulate form with particles larger than 5 pm, orlarger than 10 pm or larger than 15 pm in at least one direction. Further,according to at least one embodiment of the invention the semiconductingparticles are smaller than 100 pm, or smaller than 50pm in at least onedirection.
    According to at least one example embodiment of the invention thesemiconducting particles is selected from group IV or lll; or wherein saidsemiconducting particles are being selected from group IV or lll in mixturewith elements of group V; or wherein said semiconducting particles are beingselected from a group consisting ofSi, Ge, AIP, AlAs, GaN, GaAs, lnN, lnPand lnAs; or wherein said semiconducting particles are n- or p-doped silicon.
    According to at least one example embodiment of the invention thesemiconducting particles are obtained from a silicon wafer, e.g. by crushingthe same. According to at least one example embodiment of the invention asingle crystal silicon wafer with a resistivity of 0.01-0.02 Qcm and which isdoped with antimony is used as the semi-conducting material.
    According to at least one example embodiment of the invention the firstelectrode comprises metal, such as aluminium, silver or combinations thereof.
    According to at least one example embodiment a flexible substrate withe.g. an aluminium foil laminated on top ofa PET substrate may be used asthe first electrode. The aluminium foil may be patterned with a 7 photolithographic process where a pattern is defined and etched by aphotoresist and buffered phosphoric acid, respectively, or the aluminium canbe deposited on the flexible substrate via the means of dry phase patterning.There are numerous other ways of providing the electrode, such as, among many others, printing of silver on a substrate.
    According to at least one example embodiment of the invention theinterface between the semiconducting layer and the first electrode constitutesa rectifying contact. According to at least one example embodiment of theinvention this rectifying contact is a Schottky contact.
    According to at least one example embodiment of the invention thesecond electrode comprises a metal, electrically conductive polymers, carbonbased materials or combinations thereof.
    According to at least one example embodiment of the invention thesecond electrode may comprise carbon, and at manufacturing be provided inthe form of carbon ink or a carbon tape, or a carbon tape coated with nickel.
    According to at least one example embodiment of the invention theinterface between the semiconducting layer and the second electrodeconstitutes a non-rectifying contact.
    According to one embodiment of the invention the diode may form a part of an electronic circuit e.g. in flexible electronics.
    According to at least a second aspect of the invention a method forproviding a diode comprising the steps of: - providing a substrate whereon a first electrode is arranged- providing a semiconducting layer in physical contact with and atleast partially on top of said first electrode wherein said layer isprovided by first preparing a solution of glycerol, nano-fibrillatedcellulose (NFC), and semiconducting particles- forming at least a portion of said solution into a layer andthereafter drying said layer; wherein said dried semiconductinglayer comprises glycerol in the range of 5 wt% to 75 wt%, nano- 5 8 fibrillated cellulose (NFC) in the range of 10 wt% to 50 wt%, andsemi-conducting particles in the range of 5 wt% to 50 wt% - providing a second electrode in physical contact with and atleast partially on top of said semiconducting layer.
    Effects and features of this second aspect of the present inventiveconcept are largely analogous to those described above in connection withthe first aspect of the inventive concept. Embodiments mentioned in relationto the first aspect of the present inventive concept are largely compatible withthe second aspect of the inventive concept.
    According to at least one embodiment of the invention the semi-conducting material is prepared by crushing and/or milling of a semi-conductor, e.g. silicon particles are prepared by crushing and/or milling siliconwafers. The particles may subsequently be fractioned by the use of e.g. asieve machine. Optionally, silicon wafers may be used for the preparation ofthe semi-conducting material and may for example be a single crystal siliconwafer with resistivity of 0.01-0.02 Qcm and doped with antimony. However, there are also other ways of obtaining the particles.
    The semiconducting layer may be formed by using a casting process.According to at least one embodiment of the invention the semiconductinglayer is formed by casting said solution of glycerol, nano-fibrillated cellulose(NFC), and semiconducting particles.
    Brief description of the drawinqs The above objects, as well as additional objects, features andadvantages of the present invention, will be more fully appreciated byreference to the following illustrative and non-limiting detailed description ofpreferred embodiments of the present invention, when taken in conjunctionwith the accompanying drawings, wherein: Figure 1 is a schematic cross-sectional view of a diode in accordancewith at least one example embodiment of the invention; Figure 2 is a schematic cross-sectional view of a diode in accordancewith example embodiments of the invention; Figure 3 is a schematic top view of the different designs of the firstelectrode in accordance with at least one example embodiment of theinvention; Figure 4 is SEM micrographs of the semiconducting layer inaccordance with at least one example embodiment of the invention; Figure 5 is a graph showing the frequency response of a diodeaccording to at least one example embodiment of the invention; Figure 6A (solid line) is a graph showing the current-voltage-curve of adiode on a linear scale in accordance with at least one example embodimentof the invention; Figure 6B (solid line) is a graph showing the current-voltage-curve of adiode on a semi-log scale in accordance with at least one example embodiment of the invention.
    Detailed description of preferred embodiments of the invention The above, as well as additional objects, features and advantages ofthe present inventive concept, will be better understood through the followingillustrative and non-limiting detailed description of example embodiments ofthe present inventive concept, with reference to the appended drawings.
    Various aspects of the above-referenced methods, processes, devicesand systems will now be presented. ln presenting these aspects, embodiments will be used to illustrate features of such methods and systems. lt should be understood that these embodiments are shown by way ofexample only, and are not intended to be limiting in any way. The inventiveconcept as defined by the appended claims may be embodied both in theseand in numerous other forms. While these embodiments illustrate variouscombinations of elements and acts, it should be appreciated that some or allof such elements or acts may be assembled or practiced in other ways, withor without still further elements or acts, while still practicing the inventive conceptFigure 1 shows a diode 100 which comprises a first 102 and a second electrode 106, a semiconducting 104 layer comprising semiconductingparticles at least partly embedded and a mixture of glycerol and cellulose based material, wherein said cellulose based material is nano-fibrillatedcellulose (NFC). The first 102 and second electrodes 106 and thesemiconductor layer 104 are at least partially stacked on top of each other ina first direction. Hence the semiconducting layer 104 is sandwiched inbetween the first 102 and the second electrode 106. The amount of glycerolpresent in the semiconducting layer is in the range of 5 wt% to 80 wt%, andthe amount of nano-fibrillated cellulose (NFC) present in the semiconductinglayer is in the range of 10 wt % to 50 wt%. The interfaces between thesemiconducting layer and the first electrode forms a rectifying contact, whilethe interface between the semiconducting layer and the second electrodeforms a non-rectifying contact.
    The overall diode performance is mainly dependent on the propertiesof the interfaces between the first electrode and the semiconducting layer aswell as between the semiconducting layer and the second electrode; thediode could have any shape in the plane not shown in Figure 1. Actually, itmay be sufficient that just one semiconducting particle is in contact with boththe first and the second electrode. The resulting current throughput andrectification ratio of the diode device is mainly influenced by the doping leveland, hence, the bulk conductivity of the semiconducting particles, thethickness of the oxide layers, and the energy barriers at the interfaces.Furthermore, the defect levels, the vertical and lateral conductivity in the firstand second electrodes as well as the lateral conductivity in any assistingelectrode come second in the set of parameters that affect the currentthroughput and rectification ratio.
    Figure 2 shows a diode 200 in accordance with at least oneembodiment of the invention. On top of a substrate 202, e.g. PET, a firstelectrode 204 is provided. This first electrode 204 can also be referred to asthe bottom electrode of the diode. The first electrode 204 can for example bean aluminium electrode. On top of the first electrode there is asemiconducting layer 206 according to at least one example embodiment ofthe invention. This semiconducting layer 206 comprises semiconductingparticles 208, NFC 210 and glycerol. According to at least one example 11 embodiment of the invention the semiconducting layer 206 partly covers thefirst electrode 204. The contact between the first electrode 204 and thesemiconducting layer 206 may be a Schottky contact. On top of thesemiconducting layer 206 there is a second electrode 212. Hence, the semi-conducting layer 206 is sandwiched in between the first 204 and the secondelectrode 212. ln this embodiment of the invention the second electrode 212is a nickel-coated carbon tape; which is supplied with electrons via apowering member 215 made of e.g. aluminium. The contact between thesemiconducting layer and the second electrode may be an Ohmic contact, orat least a non-rectifying contact. Further, the second electrode 212 may becovered by an assisting electrode, e.g. aluminium foil 214. The use of anassisting electrode 214 on top of the second electrode 212 and poweringmember 215 enhances the lateral conductivity between the second electrode212 and powering member 215. The semiconducting particles 208 form alayer in said semiconducting layer 206 where single semiconducting particlesare in contact with both the bottom and the top electrode. When the particlesare arranged in such a layer a majority of the semiconducting particles that isin direct contact with the first electrode 204 may also be in contact with thesecond electrode 212. lt should be understood that the layer portion, wheresingle semiconducting particles are in contact with both the bottom and thetop electrode, is arranged at least where the two electrodes overlap eachother in the vertical direction. The portion where the two electrodes overlapeach other in the vertical direction is indicated by reference numeral 220.
    According to at least one example embodiment of the invention thethickness of the semiconducting layer 206 is in the range of 5 um to 100 um.
    The glycerol in the semi-conducting layer makes the semi-conductinglayer self-adhesive. The NFC in the semi-conducting layer makes the semi-conducting layer self-supporting.
    Figure 3 shows several examples of the aluminium bottom electrodeaccording to at least one example embodiment of the invention. The differentexamples show how the aluminium pattern of the bottom electrode can bealtered. ln more detail, the width of the bottom electrode 304, in the ydirection, is 50 um, 75 um, 100 um ,and 200 um, respectively. The elements 12 indicated with 304 and 315, corresponds to layer 204 and 215, respectively,in Figure 2.
    Figure 4 is SEM micrographs of the semiconducting layer inaccordance with at least one example embodiment of the invention; the insetin the upper right corner shows a self-supporting NFC:glycerol:Si film that isbeing removed from the Petri dish, while (a) and (b) are the SEM images fromthe top and the bottom surfaces of the film, respectively.
    Figure 5 shows a frequency response curve of a representative diodeaccording to at least one embodiment of the present invention. This particularexample of a diode according to at least one example embodiment of theinvention shows a cut-out frequency of 1.8 GHz, but the diode still produces aDC output voltage greater than 1 V at 3 GHz. The input power applied is 77mW, which corresponds to an input power that can be supplied from a mobilephone held in a close proximity to the diode when making a call within theGSM band.
    Figure 6A (solid line) shows a current-voltage-curve on a linear scale ofa representative diode according to at least one example embodiment of theinvention. Figure 6B (solid line) shows a current-voltage curve on a semi-logscale of the same representative diode according to at least one exampleembodiment of the present invention. The dashed lines in Figures 6A and 6Brepresent results of a printed diode manufactured as described in Sani et al.(All-printed diode operating at 1.6 GHz; PNAS, 2014, 111, 11943-11948).
    Example device Preparation of the device Material preparation: For preparation of Si-uPs, a single crystal Si wafer witha resistivity of 0.01-0.02 Q-cm and doped with Sb is used. First, the wafer iscrushed and then milled for 2 hours in a Retsch PM100 ball milling machine.The obtained particles are further fractioned using a Retsch sieve machinewith a 100 um stainless steel sieve, where particles that passes the sieve,also referred to as uPs, are collected and used for the diode manufacturing process. 13 An aqueous dispersion of anionic NFC gel was prepared by high-pressurehomogenization of carboxylethylated cellulose fibers and consecutively by anultrasonication centrifugation process. The resulting cellulose nanofibrilstypically have a diameter of 5-60 nm and their length vary from 100 nm to several um.
    Preparation of the film: The fractioned Si powder is then mixed with 0.5 wt%NFC water suspension and glycerol; the latter ingredient is included toenhance the surface adhesion of the dried film. The mixture is then furtherdiluted with water by a factor of two and thoroughly mixed with a shear mixerfor 3 minutes, and then further mixed with an ultrasonic gun (Sonopuls 2200)by applying 1 s pulses, at a 10% duty cycle, with 20 W power for 30-60 s. 5 gof the final mixture is cast into a petri dish with a diameter of 50 mm and isthen left to dry in ambient environment. The resulting dried film contains 12.5wt% Si-uPs, 51.5 wt% glycerol and 36 wt% NFC. The resulting films, alsoreferred to as NFC:Si-uP film or NFC:Si-uP composite film, can easily bepeeled off from the bottom of the Petri dishes. The surfaces of the two sidesof the NFC:Si film were characterized by optical profilometer and scanningelectron microscope (SEM), see Figure 4. lt can be seen that even though asieve for 100 um large particles was used, the largest particles are not larger than 50 um.
    Device fabrication: The diode structure is simply fabricated by laminating andpressing the different layers of materials together. The only equipment used isa calender machine working at room temperature. A flexible substratecomposed of 9 um Al foil laminated onto a 36 um PET foil was used. The Alsubstrate is patterned by a photolithography process, where the pattern wasdefined and etched by photoresist and buffered phosphoric acid, respectively.A piece of the NFC:Si-uPs composite film is then cut and pasted onto a e.g. 1mm wide Al strip on the pre-patterned Al substrate. The structure is thenpressed using a calender machine, with a pressure of 3 bar, which ensuresgood contact between the Al strip and the NFC:Si-uP film. A double adhesive 14 conducting tape consisting of Ni plated carbon fibers (3M 9713) (Ni/C tapehereafter), supported with a layer of Al foil on top, is then applied on top of theNFC:Si-uPs film. The entire PET/Al/NFC:Si-uP film/Ni/C/Al stack structure ispressed once more using the calender machine, again with a pressure of 3bar. The overlapping surface area of the Si film and the top electrode is 2mm2.
    A diode structure was created by incorporating the NFC:Si-uP filmbetween Al/PET and a conductive tape by using a simple “peel and stick”assembly method. Schottky junctions are formed between the Si particles andthe Al bottom electrode, while the non-rectifying, close to ohmic, contact isensured by a double adhesive conductive tape based on Ni plated carbonfibers. One of the prime advantages of using this kind of contact electrodesover the common conductive inks, such as carbon paste, is that theconductive tape cannot penetrate into, or even through, the semiconductinglayer to cause short circuits down to the bottom contact. Another function ofthe Ni/C tape is that it spans over the junction area and attaches to the PETsubstrate, i.e. it ensures a mechanically stable diode that is kept in place.
    The entire process of fabricating both the semiconducting NFC:Si-uPcomposite film and the diode is performed at room temperature. The onlymachine used in this process is a calender machine that presses andlaminates the different layers/films together.
    Characterization of the deviceDC characteristics of the diodes were measured by a Keithley 4200-SCSSemiconductor Characterization System.
    The high frequency performance of the diodes is characterized byapplying a single harmonic signal, and the output DC voltage is thenmeasured within a span of frequencies ranging from 10 MHz to 6 GHz. AnAgilent RF frequency signal generator 8665B is connected to the sample viaa 50 Q cable and a microwave Air Coplanar Probe (ACP) from CascadeMicrotech (custom made with 1250 um pitch between ground and signal probe tips), and the output signal of the sample is also probed with an ACP and connected with a 50 Q cable to an oscilloscope (Tektronix TDS3034) withthe input impedance of 1 MQ and 13 pF. The sample was connected to aninput power of 19.9 dBm via a 1 dB attenuator in order to reduce signalreflections. To measure the power harvesting capability of the diode, a set-upsimilar to the high frequency measurement is used, but a resistive load isconnected in series to the diode instead of the oscilloscope. The voltage dropacross the resistive load is measured at input frequencies of 0.9 and 1.8 GHzwhile the load is varied between 50 Q and 1 IVIQ. o Properties of the NFC:Si-/,tP film: The NFC:Si-uP films are entirely self-supporting and semitransparent, and can easily be peeled off from the petridish by using ordinary tweezers. The film is slightly sticky and exhibit self-adhesive surface properties due to the presence of glycerol. The bottomsurface, i.e. the side that is in contact with the Petri dish surface duringdrying, is relatively more adhesive than the top surface. This probablyindicates that there is a slightly higher glycerol content at the bottom sectionof the film as compared to the top volume. SEM images, Figure 4, showedthat although the sieve used to filter the Si particles is 100 um, the crossingline lengths of the largest particles are shorter than 50 um.
    The NFC matrix has a thickness of 10-15 um according to the opticalprofilometer measurements. The SEM images showed that all Si-uPs arecovered with NFC along the top surface. This NFC top-layer is probably verythin for the larger Si-uPs that are extending outside the NFC film matrix; whileat the bottom surface many of the particles are not covered by NFC. TheSEM images taken from the top surface of the films before and after they arepressed using the calender machine suggest that the mechanical pressureduring calendering might cause the thin NFC layer to rupture, and therebyensuring good electrical contact between the Si-uPs and the electrodes.
    Device structure and mechanism: The Si-uPs embedded in the NFC film form Schottky contacts to the Al bottom layer. The nature of the contact between a 16 NFC:Si-uP film and the Ni/C tape electrode is ohmic, or close to ohmic, or atleast non-rectifying. This was confirmed by I-V measurements performed on asymmetric structure of the film sandwiched between two layers of Ni/C tape.The use of an extra Al foi| on top of the Ni/C tape enhances the |atera|conductivity of the top contact, which bridges between the top side of thesemiconducting film and the electrode (315 in Figure 3) on the substrate.
    Diode performance and modeling: ln all the measurements and modeling thecurrent level is here the preferred description of the charge transport throughthe device over the current density. This is because the semiconducting layerof the diode is heterogeneous and consists of multiple particles, whichtogether contributes in parallel to the resulting measured current. Also, eachparticle contributes differently to the electrical conduction depending on itsshape, orientation, size, etc., therefore the current density would not be anaccurate term to use for this device structure.As seen in Figure 6A, the device has a sharp turn-on voltage at around 0.5 V, and a rectification ratio up to 4x103 is achieved below 2 V bias. Thisindicates that a good Schottky contact is established between the Al bottomelectrode and the Si particles. At higher voltages the leakage currentincreases, resulting in lower rectification factor. The relatively high leakagecurrent is probably due to the Schottky barrier lowering and defect levels onthe surface of the particles. However, the diode performance is still sufficientin e.g. many low-power (mW range) energy harvesting applications. Within abatch of six samples, two have a current level on the order of 10'5 A, two haveabout 106 A and two have 10'2A of forward current at 2 V. All of the samplesin the batch exhibit a rectification ratio up to 100-1000 below 2 V bias. Thecurrent-voltage relationship of a Schottky diode can be expressed as: il ~ 17 Is is the reverse current, RS is the series resistance, n is the ideality factor ofthe diode and q and T are the elementary charge and the absolutetemperature, respectively. The ideality factor, which equals 1 for an idealdiode, is an indication of the voltage dependence of the barrier height. The y-axis intercept of the linear part of the logarithmic-linear plot of the I-V curvegives the reverse current and the ideality factor can be calculated using theslope of the same curve.
    Furthermore, the possibility of reconfiguring the sticker label diode wassuccessfully tested. lt was possible to lift off the upper part of the diodeconsisting of the NFC:Si-uP film laminated with the Ni/C conductive tape. Thispart of the diode stack was then transferred to another substrate, and after anadditional calendering process step a new diode with similar I-V performance,as compared to the initial diode, was obtained.
    Since energy harvesting and AC to DC conversion are among the mainapplications that are considered for this type of flexible diode, it is important tocharacterize the range of operating frequencies of the diode. This is verifiedby the frequency response of the diode which is characterized by applying asingle harmonic signal, and measuring the output DC voltage while sweepingthe input frequency. At high frequencies the input signal at each node in themeasurement circuit can be reflected back and forth if the input and outputimpedance are not matched. This results in an increase or a decrease of theoutput signal depending on the phase difference between the reflected andthe incoming wave. The phase difference between the two signals dependson different parameters such as input frequency, load, cable lengths etc. Thiseffect appears as fluctuations in the output DC level as the frequency isvaried. An averaging approach is used to estimate the cut-off frequency of thedevice, which is defined as the frequency where the output power drops to half (or equivalently the voltage drops to l/x/ï) of the corresponding value atthe lowest frequency (10 MHz in our measurement). The frequency responseof a representative diode, shows a cut-off frequency of 1.8 GHz even thoughthe diode still produces a DC output voltage greater than 1 V at 3 GHz. Theapplied input power is 18.9 dBm (77 mW, after subtracting the damping effect 18 from the attenuator), and this is a power that can be supplied for example bya mobile phone that is held in close proximity to the diode while making a callwithin the GSM band. Among a batch of six devices, two of them have a cut-off frequency above 1 GHz. However all of the devices have at least a cut-offfrequency of 100 MHz.
    The overlapping surface area of the two electrodes sandwiching theNFC:Si-uP film is 2 mm2. The surface area of the Schottky contact is,however, much smaller as compared to the projected surface area of theparticles since only a fraction of the surface area of each particle is in contactwith the Al substrate.
    The output power for a resistive load is measured at two fixedfrequencies, 0.9 GHz and 1.8 GHz, which correspond to the two GSMfrequencies, by using the same set-up and input power as in the frequencyresponse measurement. A variable load resistor is connected to the circuitand the output power is measured while the load resistance is varied between50 Q to 1 MQ at a constant input power of 77 mW. As the load resistance isincreased, the voltage drop across the load is also increased while the currentsimultaneously drops. The power, which is the product of current and voltage,is low as long as the resistance is very low (i.e., close to short circuit), sincethe voltage drop is small. Adjusting the load resistance to a very high value(i.e., close to open circuit) also results in a low output power since the currentis negligible. On the contrary, the output power has a peak when theresistance of the load is equal to the real part of the output impedance, whichfor this diode appears to be 800 Q and 1400 Q at the input frequencies of 0.9MHz and 1.8 MHz, respectively. The maximum output power available withthe mentioned input is around 1.26 mW at 0.9 GHz and 0.25 mW at 1.8 GHz.Although these values are relatively low as compared to commercial diodes,they are sufficient for powering low input power devices such as printedorganic electrochromic displays and sensors. lt should be noted that themaximum output power is reached only when the impedance of the loadmatches the output impedance of the entire measurement circuit, including the diode, which is however not purely resistive.
    权利要求:
    Claims (14)
    [1] 1. A diode comprising: - a first and a second electrode; - a semiconducting layer comprising semiconducting particles atleast partly embedded in a mixture of glycerol and cellulosebased material, wherein said cellulose based material is nano-fibrillated cellulose (NFC); wherein said first and second electrodes and said semiconductor layer are atleast partially stacked on top of each other in a first direction; wherein the amount ofglycerol present in the semiconducting layer is in therange of 5 wt% to 75 wt%, and the amount of nano-fibrillated cellulose (NFC) present in the semiconducting layer is in the range of 10 wt % to 50 wt%.
    [2] 2. A diode according to claim 1 wherein the amount of glycerol present inthe semiconducting layer is in the range of 5 wt% to 80 wt%, or 10 wt% to 75wt%, or 15 wt% to 70 wt%, or 25 wt% to 60 wt%.
    [3] 3. A diode according to claim 1 or 2 wherein the amount of nano-fibrillated cellulose (NFC) present in the semiconducting layer is in the rangeof 10 wt% to 50 wt%, or 15 wt% to 45 wt%, or 25 wt% to 40 wt%.
    [4] 4. A diode according to any of the preceding claims wherein the amountof semiconducting particles is in the range of 0.1 wt% to 85 wt%, or 1 wt% to60 wt%, or 5 wt% to 30 wt%, or 10 wt% to 20 wt%.
    [5] 5. A diode according to any of the preceding claims wherein the glycerol,the cellulose based material and the semiconducting particles constitutes 75wt%, or 85 wt%, or 95 wt% of the semiconducting layer.
    [6] 6. A diode according to any of the preceding claims wherein singlesemiconducting particles are in contact with both the bottom and the top electrodes.
    [7] 7. A diode according to any of the preceding claims wherein the ionicconductivity of the semiconducting layer is lower than 1E-4 S/cm, or lowerthan 1E-5 S/cm, or lower than 1E-6 S/cm.
    [8] 8. A diode according to claim 1 wherein the size of said semi-conductingparticles are larger than 5 um in at least a first direction; and wherein the size of the semi-conducting particles is less than 100 um inat least said first direction, or less than 50 um in at least said first direction.
    [9] 9. A diode according to any one of the preceding claims wherein saidsemiconducting particles are selected from group IV or lll; or wherein saidsemiconducting particles are being selected from group IV or lll in mixturewith elements of group V; or wherein said semiconducting particles are beingselected from a group consisting of Si, Ge, AIP, AlAs, GaN, GaAs, lnN, lnP and lnAs; or wherein said semi-conducting particles are n- or p-doped silicon.
    [10] 10.electrode comprises metal, or wherein said first electrode comprises A diode according to any of the preceding claims wherein said first aluminium, silver or combinations thereof.
    [11] 11. A diode according to any of the preceding claims wherein said secondelectrode comprises a metal, electrically conductive polymers, carbon based materials or combinations thereof.
    [12] 12. A method for providing a diode comprising the steps of:- providing a substrate whereon a first electrode is arranged- providing a semiconducting layer in physical contact with and atleast partially on top of said first electrode wherein said layer is 21 provided by first preparing a solution of glycerol, NFC andsemiconducting particles - forming at least a portion of said solution into a layer andthereafter drying said layer; wherein said dried semiconductinglayer comprises glycerol in the range of 5 wt% to 80 wt%, nano-fibrillated cellulose (NFC) in the range of 10 wt% to 50 wt%, - providing a second electrode in physical contact with and atleast partially on top of said semiconducting layer.
    [13] 13. A method according to claim 12 wherein the dried semiconductinglayer is self-adhesive; and wherein said step of providing said semi-conducting layer in physicalcontact with said first electrode, comprises attaching the semi-conducting layer to said first electrode using said self-adhesiveness.
    [14] 14. A method according to claim 12 or 13 wherein said step of forming saidsemi-conducting layer comprises using a casting process when forming said semi-conducting layer.
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    同族专利:
    公开号 | 公开日
    EP3208852B1|2019-03-27|
    SE540484C2|2018-09-25|
    EP3208852A1|2017-08-23|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    EP2800102B1|2013-04-30|2018-05-23|RISE Acreo AB|Self-adhesive conductive layer|CN110098346A|2019-04-26|2019-08-06|深圳市华星光电半导体显示技术有限公司|The encapsulating structure and its packaging method of display panel|
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    优先权:
    申请号 | 申请日 | 专利标题
    SE1650220A|SE540484C2|2016-02-19|2016-02-19|Diode and method for producing the same|SE1650220A| SE540484C2|2016-02-19|2016-02-19|Diode and method for producing the same|
    EP17156691.2A| EP3208852B1|2016-02-19|2017-02-17|Diode and method for producing the same|
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