Patent Publication Number: US-2022236215-A1

Title: Plasmonic organic electrochemical transistor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims benefit of U.S. Patent Application Ser. No. 63/141,089, filed Jan. 25, 2021; the entire contents of the aforementioned patent application are incorporated herein by reference as if set forth in its entirety. 
    
    
     U.S. GOVERNMENT LICENSE RIGHTS 
     This invention was made with Government support under Award No. ECCS-1351757 awarded by NSF. The Government has certain rights in the invention. 
    
    
     BACKGROUND 
     An organic electrochemical transistor (OECT) utilizes a basic field effect transistor (FET) architecture having gate, drain, and source electrodes. However, the channel is fabricated with an organic semiconductor, rather than an inorganic semiconductor channel, between the drain and the source electrodes. The organic semiconductor channel may be a polymer. Further, the OECT has an electrolyte between the organic semiconductor channel and a gate electrode. The semiconductor channel is immersed into the electrolyte. 
     The electrolyte can be a liquid or a gel. An OECT can be formed on different types of insulating and semiconductor substrates, including fiber, paper, plastic, and elastomer. An OECT is stable in aqueous or organic electrolyte environments. 
     Drain current of an OECT is controlled by an injection of ions from the electrolyte into the organic semiconductor channel. As with other types of FETs, a supply voltage is applied between the drain and source electrodes to provide current flow between the drain and source electrodes. When a bias voltage is applied between the gate and source electrodes, ions (cations or anions) from the electrolyte are injected into the organic semiconductor channel changing electronic charge density in the organic semiconductor channel and thus the drain current. 
     Direct injection of ions from the electrolyte into the organic semiconductor channel affects a transconductance of the OECT. Therefore, any change (e.g., due to oxidation-reduction) at the gate is translated to a change in the transconductance of the OECT. The injection of ions takes place in a whole volume of the channel of the OECT, and thus a small variation in the gate voltage, e.g., due to the oxidation-reduction, is reflected in the channel by a change in the transconductance of the OECT. In metal insulator semiconductor FETs, a small variation in the gate voltage affects only two-dimensional interface between the insulator, e.g., oxide, and the channel. Because the whole volume of the channel, the OECT has enhanced transconductance and thus sensitivity in comparison to other types of FETs. Because of its aforementioned benefits, the OECT is considered for use as a highly sensitive biosensor. 
     SUMMARY 
     A plasmonic organic electrochemical transistor comprises: a channel comprising an organic semiconductor; a gate electrode comprising at least one of: an ensemble of nanoparticles and an array of nanostructures, wherein each of the least one of: an ensemble of nanoparticles and an array of nanostructures comprises localized plasmonic material; an analyte formed at least one of: (a) over the at least one of: the ensemble of nanoparticles and the array of nanostructures and (b) around the at least one of: the ensemble of nanoparticles and the array of nanostructures; wherein an electrolyte is configured to be formed at least one of: between the channel and the gate electrode and over the channel and the gate electrode; a source electrode electrically connected to a first end of the channel; and a drain electrode electrically connected to a second end of the channel which is opposite the first end. 
     A method for operating a transistor, the method comprising: applying a bias to a control electrode of the transistor, wherein the control electrode comprises at least one of: an array of nanostructures and an ensemble of nanoparticles, and wherein each of the at least one of: an array of nanostructures and an ensemble of nanoparticles comprises localized plasmonic material; receiving non-ionizing incident radiation at the at least one of: the array of nanostructures and the ensemble of nanoparticles to generate hot electrons and heat at nanoparticles of the ensemble of nanoparticles and nanostructures of the array of nanostructures; in comparison to when the non-ionizing incident radiation is not received at the at least one of: the array of nanostructures and the ensemble of nanoparticles, increasing a chemical reaction rate in an analyte, or a material or a chemical generated from the analyte, wherein the analyte is formed at least one of: (a) over the at least one of: the ensemble of nanoparticles and the array of nanostructures and (b) around the at least one of: the ensemble of nanoparticles and the array of nanostructures; in comparison to when the non-ionizing incident radiation is not received at the at least one of: the array of nanostructures and the ensemble of nanoparticles, increasing a rate of change of charge generation in the control electrode; in comparison to when the non-ionizing incident radiation is not received at the at least one of: the array of nanostructures and the ensemble of nanoparticles, increasing or decreasing a rate of change of ions injected between an electrolyte and an organic semiconductor; and for a given change in the bias between the control electrode and a non-control electrode of the transistor, enhancing an increase or a decrease of an amount of current flowing through the transistor. 
     A method of fabricating a transistor, the method comprising: forming, over a substrate, a control electrode and two non-control electrodes of a transistor, wherein the control electrode comprises at least one of: an array of nanostructures and an ensemble of nanoparticles, and wherein each of the at least one of: an array of nanostructures and an ensemble of nanoparticles comprises localized plasmonic material; forming, over the substrate, an organic semiconductor; forming an electrolyte at least one of: between the organic semiconductor and the control electrode and over the organic semiconductor and the control electrode; and forming, at least one of: over the array of nanostructures and around the array of nano structures, an analyte. 
    
    
     
       DRAWINGS 
       Embodiments of the present invention can be more easily understood and further advantages and uses thereof more readily apparent, when considered in view of the description of the preferred embodiments and the following figures in which: 
         FIG. 1A  illustrates a plan view of one embodiment of a plasmonic organic electrochemical transistor; 
         FIG. 1B  illustrates a plan view of one embodiment of a plasmonic organic electrochemical transistor of  FIG. 1A  additionally including an analyte and an optional catalyst; 
         FIG. 2  illustrates a block diagram of one embodiment of a plasmonic organic electrochemical transistor optically coupled to an optical source through an optical fiber; 
         FIG. 3  illustrates a flow diagram of one embodiment of a method of operation of a plasmonic organic electrochemical transistor; and 
         FIG. 4  illustrates a flow diagram of one embodiment of a method for making a plasmonic organic electrochemical transistor. 
     
    
    
     In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize features relevant to the present invention. Reference characters denote like elements throughout figures and text. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized, and that logical, mechanical, and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. 
     Embodiments of the invention improve transconductance, and thus sensitivity, of an OECT by utilizing a gate electrode formed by or including an array of plasmonic nanostructures and/or an ensemble of plasmonic nanoparticles, and with an analyte on and/or about the gate electrode. An ensemble of plasmonic nanoparticles means plasmonic nanoparticles where each plasmonic nanoparticle is separated from other plasmonic nanoparticles, i.e., each plasmonic nanoparticle is not in contact with another plasmonic nanoparticle. The analyte is a chemical, e.g., a bio-chemical, being sensed (or identified) and/or analyzed with a plasmonic OECT. 
     An OECT whose gate electrode formed by or comprising at least one of: (a) an array of plasmonic nanostructures and (b) an ensemble of plasmonic nanoparticles may be referred to as a Plasmonic OECT or a POECT. Each plasmonic nanostructure and each plasmonic nanoparticle is formed with localized plasmonic material. Localized plasmonic material is a material, when forming an array of nanostructures and/or an ensemble of nanoparticles, generate an electromagnetic field which resonates with an electromagnetic field of incident radiation (including a wavelength that is a resonant wavelength of the array of nanostructures and/or the ensemble of nanoparticles). For purposes of clarity, the incident radiation is non-ionizing radiation. Optionally, the incident radiation comprises an optical signal. The resonant wavelength is dependent upon dimension(s) of the array of nanostructures and/or the ensemble of nanoparticles. 
     Incident radiation means radiation incident upon the array of nanostructures and/or the ensemble of nanoparticles. The electromagnetic field from the incident radiation excites electrons in the localized plasmonic material to higher energy states. Due to the excitation, electrons can transfer from the localized plasmonic material (e.g., the to the analyte. Due to de-excitation of electrons, heat can be generated (i.e., localized heating) by the localized plasmonic material can be transferred to the analyte. Localized plasmonic material may be conductor, such as a metal (e.g., gold, silver, platinum, aluminum, or copper) or metal alloy; however, localized plasmonic material may also include without limitation transition metal nitride(s) (e.g., titanium nitride) and quasi-metal(s) (e.g., graphene). 1  Each plasmonic nanostructure has a resonant frequency corresponding to dimension(s), for example a radius of a nanohole, of the plasmonic nanostructure.  1  Thus, plasmonic nanostructure means a nanostructure formed from or comprising localized plasmonic material. Plasmonic particle means a nanoparticle formed from or comprising localized plasmonic material. 
     Plasmonic effect means generation of heat and hot electrons at a nanostructure or nanoparticle when the incident electromagnetic field is incident upon respectively the nanostructure or nanoparticle. An enhanced localized near electromagnetic field (created by the plasmonic effect) generates heat and hot electrons in the localized plasmonic material. The heat and hot electrons accelerate a chemical or a physical reaction in the analyte, or a material or a chemical generated from the analyte. A physical reaction may include generation of charged particles and/or a phase change. The chemical reaction is accelerated because the heat and the hot electrons cause chemical bonds (between atom(s) and/or ion(s) comprising molecule(s) forming the analyte or the material or the chemical generated by the analyte) to be more vigorously vibrated. Such chemical bonds are more easily broken due to the more vigorous vibration of the chemical bonds. As a result, efficiency of catalyzation of the analyte, or the material or the chemical generated by the analyte, is increased. Because a POECT enhances efficiency of catalyzation of an analyte, or the material or the chemical generated by the analyte, the POECT is able to detect lower concentrations of an analyte (or the material or the chemical generated by the analyte) in comparison to an OECT. 
     A nanostructure means a structure of matter having at least one dimension between 1 and 500 nanometers (nm), e.g., diameter or length. A nanodot, a nanohole a nanofiber, a nanotube, and a nanopillar are non-limiting examples of nanostructures. A nanoparticle means a particle of matter having at least one dimension between 1 and 100 nm in dimension, e.g., diameter. 
     Although other POECT structures with a control node and non-control nodes, exemplary embodiments of POECTs are subsequently described for pedagogical purposes.  FIG. 1A  illustrates a plan view of one embodiment of a plasmonic organic electrochemical transistor  100 . The POECT  100  comprises a plasmonic gate electrode  100 G, an electrolyte  100 E, an organic semiconductor channel  100 C, a source electrode  100 S, a drain electrode  100 D, and a substrate  100 H. The plasmonic gate electrode  100 G includes an array of plasmonic nanostructures (array)  100 A. The array of plasmonic nanostructures  100 A may be symmetric or asymmetric. The array of plasmonic nanostructures  100 A may be a two- or three-dimensional array. A symmetric array comprises nanostructures which each have the same dimension(s) and where each set of adjacent nanostructures are spaced apart by the same dimension (or distance). Optionally, the symmetric array comprises nanodots may be formed on the substrate  100 H and having the same radius, e.g., 100 nm and the same distance between the centers of adjacent nanodots, e.g., 200 nm. An asymmetric array comprises nanostructures which may be of different types, may have different dimension(s) for the same type of nanostructure, and/or may have different distances between adjacent nanostructures. 
     The source electrode  100 S and the drain electrode  100 D are each electrically connected to opposite ends of the organic semiconductor channel  100 C. At least the source electrode  100 S, the drain electrode  100 D comprise a metal or a metal alloy, e.g., gold, silver, platinum, aluminum, or copper. Optional gate, drain, and source terminals  100 GT,  100 DT,  100 ST, facilitating external electrical connection to the plasmonic gate electrode  100 G, source electrode  100 S, and the drain electrode  100 D, and the conductive lines CL electrically coupling each terminal to each electrode also comprise the metal, the metal alloy, or any other localized plasmonic material, and are formed on or above the substrate  100 H; if formed above the substrate, then there may be one or more layers of other material that separate such an element from the substrate. Thus, the electrodes, terminals, and connecting lines may be formed with the same material which is a localized plasmonic material. Optionally, the terminal is a bond pad. Optionally, the plasmonic nanostructures of the plasmonic gate electrode  100 G comprises the metal or the metal alloy. Each of the plasmonic gate electrode  100 G, the source electrode  100 S, and drain electrode  100 D are formed on the substrate  100 H. The optional terminals and conductive lines are also formed on the substrate  100 H. 
     The organic semiconductor channel  100 C is formed at least between the source electrode  100 S and the drain electrode  100 D. Optionally, the organic semiconductor channel  100 C may also be formed between the source electrode  100 S and the drain electrode  100 D. Optionally the organic semiconductor channel  100 C is a semiconducting polymer, e.g., poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). 
     The electrolyte  100 E is deposited at least one of: between the organic semiconductor channel  100 C and the plasmonic gate electrode  100 G and over the organic semiconductor channel  100 C and the plasmonic gate electrode  100 G. Optionally, the electrolyte  100 E is deposited at least one of between the analyte  100 N and the organic semiconductor channel  100 C and over the analyte  100 N and the organic semiconductor channel  100 C. Optionally, the electrolyte may be phosphate buffered saline (PBS), a salt (e.g., sodium chloride (NaCl)), fluid in a living entity (e.g., in a human for example in a brain), and/or another type of electrolyte. Optionally, the POECT  100  comprises an optional catalyst  100 M deposited at least on and/or around or about the array  100 A. As is discussed elsewhere herein, the optional catalyst  100 M may be used to facilitate a chemical reaction in an analyte. 
     The substrate  100 H may be an insulator, e.g., glass, sapphire, and/or an undoped semiconductor. Optionally, the substrate  100 H is transparent or at least translucent at a wavelength of an optical signal; this permits the optical signal  100 L to illuminate the array  100 A of the plasmonic gate electrode  100 G through the substrate  100 H. 
       FIG. 1B  illustrates a plan view of one embodiment of a plasmonic organic electrochemical transistor  100  of  FIG. 1A  additionally including an analyte  100 N and the optional catalyst  100 M. When the POECT  100  is utilized, e.g., as a biological or chemical sensor, the analyte  100 N is deposited on and/or around the array  100 A. If an optional catalyst  100 M is utilized, the analyte  100 N is deposited on the optional catalyst  100 M. Analyte means a substance that is being identified and/or characterized. Catalyst means a material used to accelerate a chemical reaction rate of the analyte. Optionally, the catalyst may be glucose oxidase and the analyte may be glucose; however, an alternate or no catalyst and/or an alternate analyte may be used. 
     For pedagogical purposes, the incident radiation will be illustrated as an optical signal. An optical signal  100 L, generated by an optical source, is incident upon the array  100 A of the plasmonic gate electrode  100 G. Optionally, the optical signal  100 L comprises substantially a single wavelength corresponding to the resonant wavelength of each nanostructure of the array  100 A. For example, the wavelength may be 650 nm or any other wavelength. The resonant wavelength of the optical signal  100 L stimulates the plasmonic effect in the array  100 A and increases a rate of reaction in the analyte  100 N (or a material or a chemical created from the analyte  100 N, e.g., by the optional catalyst  100 M). The increased reaction rate in the analyte  100 N (or the material or the chemical created from the analyte  100 N) increases a rate of generation of a type of charged particles, e.g., electrons, in the plasmonic gate electrode  100 G. 2  The increased rate of generation of charged particles increases a rate at which a bias voltage (applied by an external voltage source between the plasmonic gate electrode  100 G and the source electrode  100 S) is modified. The increased rate at which the gate to source bias voltage is modified increases the rate of change of ions injected between the electrolyte  100 E and the organic semiconductor channel  100 C. Ions may be injected from the electrolyte  100 E into the organic semiconductor channel  100 C, or vice versa. A rate of change in current flow in the organic semiconductor channel  100 C (between the drain electrode  100 D and source electrode  100 S) is increased or decreased due to the respective increased or decreased rate of change of injected ions. Thus, as a result, a transconductance of the POECT  100  is respectively increased or decreased.  2  If the analyte is glucose and the catalyst is glucose oxidase, gluconolactone and hydrogen peroxide are generated. The hydrogen peroxide decomposes into water and oxygen while releasing electrons. 
     For example, if a positive bias voltage is applied between the plasmonic gate electrode  100 G and the source electrode  100 S and electrons are generated in the plasmonic gate electrode  100 G, then an additional voltage is generated at the gate. Therefore, the resulting effective gate voltage (e.g., more positive when oxidation take place; less positive when reduction take place) drives the transconductance. The effective gate voltage may be determined by equation: 
     
       
         
           
             
               
                 V 
                 g 
                 
                   e 
                   ⁢ 
                   f 
                   ⁢ 
                   
                     f 
                     = 
                   
                 
               
               ⁢ 
               
                 V 
                 g 
               
             
             + 
             
               
                 ( 
                 
                   1 
                   + 
                   γ 
                 
                 ) 
               
               ⁢ 
               
                 
                   k 
                   ⁢ 
                   T 
                 
                 
                   2 
                   ⁢ 
                   e 
                 
               
             
           
         
       
     
     ln [reactant] where V g   eff  is an effective voltage, V g  is a gate voltage, y is a channel to gate capacitance ratio, k is the Boltzmann constant, T is a temperature, e is an electronic charge, and [reactant] is a concentration of a reactant, e.g., H 2 O 2 , that generates charge, e.g., by oxidation. From the equation, it is clear that as the concentration of the reactant increases, the effective gate voltage increases. As a result of the increased positive bias, more cations  100 O are injected from the electrolyte  100 E into the organic semiconductor channel  100 C. These cations compensate for anions, e.g., sulfonate anions, present in the organic semiconductor channel  100 C, e.g., in the PSS part of the organic semiconductor channel  100 C. As a result, the holes that are extracted at the drain are not replenished at the source which decreases the drain current and makes the device switch to a depletion state. Note, because charged particles of either positive or negative polarity may be generated in the plasmonic gate electrode, ions of either positive or negative polarity may be injected from the electrolyte  100 E into the organic semiconductor channel  100 C, and a bias voltage of either a positive or a negative polarity may be applied across the plasmonic gate electrode  100 G and the source electrode  100 S. 
       FIG. 2  illustrates a block diagram of one embodiment of a plasmonic organic electrochemical transistor optically coupled to an optical source through at least one optical fiber. Optionally, the POECT  200  may be implemented as illustrated in  FIG. 1A or 1B . An optical source  220 A, e.g., a laser, generates an optical signal  200 L. The optical source  220 A is optically coupled to the POECT through at least one optical fiber (optical fiber(s))  220 B. One end of the optical fiber may terminate into a surface of the substrate  100 H opposite a surface of the substrate on which the array  100 A (and thus the analyte  100 N and optional catalyst  100 M) are formed. If the substrate  100 H is transparent, or at least translucent, at the wavelength of the optical signal  200 L, then the optical signal  200 L will stimulate (or induce) a plasmonic effect. Although optical fiber(s)  220 B are illustrated in  FIG. 2 , the optical signal  200 L may be propagated alternatively or additionally though an alternative type of optical waveguide, e.g., a planar optical waveguide (e.g., made with silicon nitride and silicon dioxide), and/or through free space. 
       FIG. 3  illustrates a flow diagram of one embodiment of a method  300  of operation of a plasmonic organic electrochemical transistor. The blocks of the flow diagram have been arranged in a generally sequential manner for ease of explanation; however, it is to be understood that this arrangement is merely exemplary, and it should be recognized that the processing associated with the methods (and the blocks shown in the Figures) can occur in a different order (for example, where at least some of the processing associated with the blocks is performed in parallel and/or in an event-driven manner). The flow diagram of  FIG. 3  need not only be implemented with the structure illustrated with respect to  FIGS. 1A-2 . 
     In block  300 A, a gate to source bias voltage is applied across gate and source electrodes, and a drain to source supply voltage is applied across drain and source electrodes. In block  300 B, incident radiation, e.g., an optical signal, is received at an array of nanostructures and/or an ensemble of nanoparticles of a plasmonic gate electrode, where the incident radiation comprises a wavelength that stimulates a plasmonic effect in the plasmonic gate electrode (e.g., in the array of nanostructures and/or the ensemble of nanoparticles). Optionally, the optical signal comprises substantially a single wavelength. 
     In block  300 C, a chemical reaction rate in an analyte (or a material or a chemical generated from the analyte) on and/or around the array is increased in comparison to when no incident radiation is received at the array of nanostructures and/or the ensemble of nanoparticles of the plasmonic gate electrode. In block  300 D, a rate of charge generation in the plasmonic gate structure is increased in comparison to when no incident radiation is received at the array of nanostructures and/or the ensemble of nanoparticles of the plasmonic gate electrode. In block  300 E, a rate of change of ions injected between an electrolyte and an organic semiconductor channel is increased or decreased in comparison to when no incident radiation is received at the array of nanostructures and/or the ensemble of nanoparticles of the plasmonic gate electrode. Whether the rate increases or decreases depends upon a type of reaction taking place at the plasmonic gate electrode and the analyte. 
     In block  300 F, for a given change in gate to source bias voltage, an increase or decrease in an amount of current flow in the organic semiconductor channel (between the drain and source terminals) is enhanced in comparison to when no incident radiation is received at the array of nanostructures and/or the ensemble of nanoparticles of the plasmonic gate electrode. Thus, POECT transconductance is enhanced. 
       FIG. 4  illustrates a flow diagram of one embodiment of a method  400  for making a plasmonic organic electrochemical transistor. In block  400 A, drain, source, and plasmonic gate electrodes are formed on and/or over a substrate. Optionally, the terminals and the conductive lines are also formed on the substrate. The drain electrode, source electrode, plasmonic gate electrode, drain terminal, source terminal, gate terminal, and/or conductive lines may be formed at the same time, e.g., with the same manufacturing step(s). Optionally, block  400 A is implemented as follows. A first mask of a polymer, e.g., polyacrylonitrile (PAN), may be formed by spin-coating the polymer on a mold, e.g., made from etched silicon, and then annealing, e.g., at 105 degrees Celsius. The mold includes raised portions that generate openings in the first mask defining the nanostructures of the array, the electrodes, the terminals, and/or the conductive lines. The first mask is then removed from the mold. Optionally, the dimensions of the openings, particularly for the nanostructures, may be increased by etching the mask, e.g., with a plasma etching. The first mask may have more than one reticle, where each reticle comprises a POECT. The first mask is then placed over the substrate. Localized plasmonic material is deposited, e.g., using chemical vapor deposition, plasma deposition, or physical vapor deposition, through certain openings in the mask to form electrodes and optionally connection lines; however, the localized plasmonic material does not fill openings in the first mask defining nanostructures. Thus, nanoholes are formed, and are electrically connected by the localized plasmonic material surrounding each opening in the first mask and of the nanostructure array; such localized plasmonic material surrounding the openings forms the gate electrode. The localized plasmonic material is used to form the drain, source, and plasmonic gate electrodes comprising an array of nanostructures and/or an ensemble of nanoparticles. Optionally, the localized plasmonic material is used to form the conductive lines. Each of the drain electrode, the source electrode, the plasmonic gate electrodes, the organic semiconductor channel, and the conductive line(s) may be formed on and/or above the substrate. 
     In block  400 B, the organic semiconductor channel is formed on and/or over the substrate, and optionally over at least a portion of one or both of the source electrode and the drain electrode. Optionally, the organic semiconductor channel may be formed by placing a second mask over the substrate with the deposited localized plasmonic material, and depositing, e.g., with spin coating or another type of deposition, and organic semiconductor. Optionally, the organic semiconductor is formed in opening(s) in the second mask. Optionally, the organic semiconductor is formed on and/over the substrate. If spin coating is used, then optionally a 2000 rpm spin speed may be used for thirty seconds; after finishing spin coating, then optionally annealing the substrate with the organic semiconductor for ten minutes at 130 degrees Celsius; however, the foregoing parameter values may be varied. The second mask is then removed. The second mask may be formed like the first mask. Alternatively, the first and/or second mask can be formed in alternative ways, e.g., using conventional semiconductor manufacturing techniques such as depositing and exposing photoresist to form a mask. 
     Optionally, in block  400 C, the optional catalyst is deposited on and/or around the array. The optional catalyst may be deposited by pipette(s), microfluidic channel(s), and/or any other fluidic device(s). 
     In block  400 D, the electrolyte is formed at least between an organic semiconductor channel and the plasmonic gate electrode  100 G. The electrolyte may be formed, e.g., deposited, using pipette(s), microfluidic channel(s), and/or any other fluidic device(s). 
     In block  400 E, analyte is formed on and/or around the array. If the optional catalyst is utilized, the analyte is formed on the catalyst. The analyte may be formed, e.g., deposited, using pipette(s), microfluidic channel(s), and/or any other fluidic device(s). 
     Terms of relative position as used in this application are defined based on a plane parallel to the conventional plane or working surface of a material (e.g., a layer or a substrate), regardless of orientation. Terms such as “on,” “higher,” “lower,” “over,” “top,” and “under” are defined with respect to the conventional plane or working surface being on the top surface of a layer or substrate, regardless of orientation. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.