FI116704B - Methods and arrangements for providing and utilizing improved electronic conductivity in an organic thin-film transistor - Google Patents

Description

116704

Methods and Arrangements for Improving and Conducting Electronic Conductivity in an Organic Thin Film Transistor - Förfar-anden och arrangemang för att ästadkomma ooh utnyttja förbättrad electro-nisk ledningsförmäga i en organic tunnel film transistor 5

The invention generally relates to the use of organic materials in the manufacture of thin-film transistors and to the utilization of thin-film transistors thus produced. In particular, the invention utilizes certain electrical conductivity properties of organic thin-film transistors and demonstrates how the correct choice of materials and manufacturing methods can lead to the utilization of organic thin-film transistors, even in entirely new areas.

The basic technology of organic thin-film channel transistors (OFET) is known and well established. Figure 1 is a cross-sectional view of a basic OFET structure known as a "top-gate" structure. The substrate, or substrate 101, forms a flat non-conducting support surface 15 on which are deposited other layers. On top of the substrate 101 are the source and sink electrodes 102 and 103 made of a highly conductive material, such as a thin layer of metal or a conductive polymer. The active layer 104 connects the source and drain electrodes 102 and 103 to each other. In some source works, the active layer is called the channel layer. The active layer 104 is made of a semiconductor organic polymer; most preferably conjugated polymers are used.

On top of the active layer 104 is an insulating layer 105 which serves to act on the electrical | insulation. Thus, the insulating layer 105 has good electrical insulating properties and is made of a polymer (eg, polystyrene) or an inorganic material (eg, S1O2). The dielectric layer 105 may be constructed from a plurality of overlapping sublays to achieve certain properties such as surface modification, diffusion barrier, or solvent compatibility. On top of the insulating layer 105 is: * 1 ': a gate electrode layer 106 made of metal or a highly conductive polymer.

/. The structure also includes various connecting wires and terminals connected to the electrodes, but for the sake of clarity of the drawing, they are not shown in the figure.

* 1111

The structure of Fig. 1 functions as a channel transistor so that the electric potential of the gate 106 is> »... This increases the number of charge carriers in the active layer 104, which affects the ability of the electric current to pass through it. In its simplest form, the OFET of Fig. 1 acts as a switch, whereby at one gate potential value, the electric current 116704 2 can travel between the source and the drain, while at another gate value the current flow is prevented. One of the key factors affecting the operation of OFET is the mobility of reservation carriers in duct material. Typically, the goal is high mobility, since the high mobility of the charge carriers in the channel means 5 better sensitivity, i.e. fast switching time and strong correspondence between the gate voltage and the source drain current.

The current state of the OFET technology is discussed, for example, in US 2003/0059984 A1, WO02 / 095805, US6380558, US6506438, US6429 450, WO99 / 10939 and US63444660. In addition, certain methods of fabricating semiconductor thin film structures are discussed. EP-A1 -0 701 290, US 6 150 692 and US 2002/0158574 A1. In the manufacture of thin-film transistors, organic and inorganic materials can be combined, but the use of inorganic materials and small organic molecules generally requires a complex vacuum-vaporization process and expensive equipment, thereby losing many of the benefits of solution-form organic materials.

Most of the functional properties of the transistor are related to the formation of a current channel through the active layer between the source and drain electrode. Impurities, or doping agents, have a decisive influence on the properties of semiconductor materials, so the interface between the active layer and the gate insulation, in particular, should be kept free of any impurities. For example, US 2003/0059984 A1 describes how source and sink electrodes alone can be formed on a substrate in an i · air environment, after which the substrate must be introduced into an inert (nitrogen) atmosphere for the remainder of the process. It is stated in that publication that even measurements of the use of OFETs should be made in an inert atmosphere.

Other disadvantages of the known manufacturing processes include the heavy-duty cleaning and surface preparation steps, which are particularly required if the silica (SiO 2) is used as the gate insulation. The choice of materials matters: pre- ···: as a source, the materials of the source and sink electrodes must, on the one hand, adhere well to the substrate and, on the other hand, provide good electrical contact with the conjugate of the active layer; ': 30 g of polymeric material. In order for the gate voltage to effectively modulate the duct current, the gate insulation material must have a high dielectric constant and the gate insulation should be made as thin as possible. The traditional properties of organic insulators make it difficult to achieve these objectives, whereby the operation of the device often requires relatively high voltages. High voltages, in turn, increase the risk of break-throughs and reduce the usefulness of the circuits. Bao, Z. et al., "Soluble and processable regioregular poly (3-hexylthiophene) for thin film 116704 3-field transistor applications with high mobility", Applied Physics Letters, 69 (26) p. 4108-4110 (1996), it is found that conventional polymer transistors require a gate voltage of 20-30 volts or more in order to achieve sink current saturation and transistor-typical 1-V curves (current-voltage curves) which indicate how the 5 gate voltage modulates the source sink current.

It is an object of the present invention to provide methods and arrangements for manufacturing and utilizing (in particular organic) thin-film transistors at low voltage requirements. It is a further object of the invention to provide practical applications of organic thin-film transistors which do not require laboratory conditions. It is also an object of the invention to provide cheap serial production of circuits based on organic thin film transistors according to the invention.

The objects of the invention are achieved by the use of a hygroscopic polymer in the gate insulation layer of an organic thin film transistor and by allowing ambient humidity to influence the electron current in the channel of the organic thin film transistor. Certain aspects of the Kek-15 invention are also accomplished by allowing the upper layer molecules to be mechanically drawn in a specific direction during the contraction manufacturing process, increasing orientation within the active layer.

The thin-film transistor device according to the invention comprises: - an organic semiconductor layer, - v '20 - a source electrode and a drain electrode connected to one another by an organic semiconductor'! through the layer, * ":. - a gate electrode and a dielectric layer made of a hygroscopic polymer between an organic semiconductor layer and a gate electrode; activity through ionic effects.

; ' The invention also relates to an electronic measuring circuit comprising: ...,: - a thin-film transistor device, as described above, exposed to ambient conditions · 30,: - a biasing circuit for supplying a bias voltage to said thin-film transistor operating system in said thin-film transistor device, said thin-film transistor device, and 116704 4 - an indicator circuit coupled to said thin-film transistor device, arranged to detect a change in current modulation capability of said thin-film transistor device due to changing environmental conditions.

The invention further relates to a method for manufacturing a thin film transistor device. The method comprises the steps of: - forming an organic semiconductor layer to combine a source and a sink electrode pair, - forming a dielectric layer of a hygroscopic polymer to cover a portion of the organic semiconductor layer, and 10 channel area; and characterized in that: - in the method, the dielectric layer is arranged to absorb moisture in the form of a polar-15 solvent to improve the performance of the thin-film transistor device by ionic effects.

Hygroscopic polymer refers to a polymer that absorbs or absorbs moisture from its surroundings. According to a very narrow interpretation, the terms "hygroscopicity" and "moisture" are solely related to the absorption of water vapor. However, solvents other than water must also be considered in the context of the present invention. i '·': In this specification and the related claims, hygroscopicity refers to the ability of solvent vapor to absorb electrolyte in and / or on the surface of a hygroscopic material if ions are present. Similarly, in this document the term moisture refers to vapor. 25 and / or a liquid solvent, such as e.g. water, ethanol and methanol. The effect of the polarity of such a solvent is also discussed later in this specification.

Traditionally, the hygroscopicity of certain polymers has been considered a drawback. in thin-film transistor technology: according to the state of the art, OFET trans; The materials used to make the sensors should be kept as clean as possible to achieve controlled and predictable performance. Preparation and Measurements: · *: have taken place in an inert environment and / or OFETs have been covered with impermeable coatings prior to exposure to uncontrolled environmental conditions.

116704 5

According to the invention, the gate insulating layer of the organic thin film transistor should contain a hygroscopic polymer. In the research leading up to the invention, it was found that certain properties of OFET transistors were significantly improved when the ambient humidity was allowed to be absorbed into the dielectric layer. The observed effects indicate that the moisture in the dielectric layer causes phenomena that, as measured, appear to be associated with exceptionally good charge carrier mobility in the duct, whereby high electrical current at low gate voltage and excellent current modulation at the gate voltage and low drainage bandwidth can be detected. More specifically, the saturation current appears to be stable as long as the environmental parameters are kept constant during the measurement. Another stable current is obtained if, for example, the humidity level is changed to another constant value. Similar well-defined behavior is observed over a wide range of moisture levels and other environmental parameters.

One technique for manufacturing OFET transistors has also been found to increase the orientation of molecules in duct material, which is generally a beneficial feature. In said manufacturing method, a top-gate structure was formed in which a generally circular gate electrode is located on a duct-insulating layer. The circular gate electrode was formed by placing a drop of liquid polymer-20 solution at a suitable location and allowing the solvent to evaporate. During evaporation, the gate: electrode shrunk, causing a dielectric pulling mechanical force that was J · V high enough, even mechanically, to cause the active layer molecules to be somewhat ordered.

The novel features considered to be characteristic of the invention are set forth in detail in the appended claims. However, the invention itself, its structure and principle of operation, as well as other objects and advantages of the invention, will be described below with reference to certain specific embodiments and with reference to the accompanying drawings.

Fig. 1 shows a traditional OFET structure, Fig. 2 illustrates the principle of the layered structure of the invention, Fig. 3 shows certain process steps of the method according to the invention, Fig. 4 schematically shows a dual-fold pattern, *: Fig. 5 Fig. 6 is a plan view of the OFET transistor of Fig. 5, Fig. 7 is a view from above of Fig. 5, Figs. Fig. 9 illustrates a switching speed of an OFET transistor according to the invention, Fig. 10 shows a switching speed of a prior art OFET transistor, and Fig. 11 shows a humidity detector according to an embodiment of the invention.

Exemplary embodiments of the invention exemplified in this patent application are not to be construed as limiting the applicability of the appended claims. The verb "comprising" is used in this patent application as an open limitation which does not exclude features not mentioned herein. The properties mentioned in the dependent claims may be freely combined with one another unless otherwise specifically stated.

Figure 2 is a cross-sectional view of the so-called organic polymer layers. sandwich structure according to an embodiment of the present invention. The lowest one is the active layer 201, which has two other layers, referred to herein as the intermediate layer 202 and the transducer layer 203. The horizontal dimension of the active layer 201 and the intermediate layer 202 is not important, but the transducer layer 203 assumes a limited dimension at least is parallel to the cross-sectional plane shown in Figure 2. Typical ways of meeting such a criterion are e.g. implementing transducer layer 203 as a circular spot, in which case the dimension d of Figure 2 corresponds to the diameter of the spot, or transducer layer 203 as a line across the surface of layer i, wherein dimension d corresponds to the line width. Certain interlayer physical and chemical interactions, which will be described later, will cause a change in a certain portion of the active layer 201. The altered 25 portions of the active layer may be separately called the changed active layer portion 204. It is * *, '·. Figure 2 is marked with a cross line.

According to the present invention, the key properties of the layers of Figure 2 are as follows:, ·, - the active layer 201 consists of a semiconductor organic polymer '·'; 30 - the transducer layer 202 consists of an insulating hygroscopic organic polymer: i - the properties of the transducer layer 203 and / or the process of forming the transducer layer 203 on the stack layer 203 and the transducer layer 202 cause changes which give rise to the altered active layer portion 35 204.

116704 7

Let us first consider certain physical changes that occur to the altered active layer portion 204 by certain manufacturing steps. For the time being, it is forgotten that certain other components may be present and only the three layers shown in Figure 2 are considered. It is assumed that the process for making an organic thin-film semiconductor device includes the steps of Figure 3. In step 301, an active layer is formed. Typically, at step 301, a semiconducting organic polymer film is formed on the substrate at a rotation speed of 1000-3000 rpm from a solution of 2 to 10 mg / ml. The resulting film has a thickness in the order of 10-100 nm. In step 302, the active-10 layer formed in step 301 is covered with a hygroscopic dielectric layer, typically at a rotation speed of 500-3000 rpm, from a 50-150 mg / ml solution. The resulting hygroscopic insulating layer has a thickness of hundreds of nanometers to a few micrometers, but typically less than 2 micrometers.

Instead of the spin technique, steps 301 and 302 can be performed using solution casting or printing. In addition, other spin parameters may be used when using the spin coating technique, depending, for example, on the concentration of the stock solution. The above parameter ranges are to be considered as examples only and are not intended to limit the scope of the present invention. One skilled in the art will be able to experiment with other ranges of parameters to find other ways to achieve corresponding performance characteristics for the resulting organic thin-film semiconductor devices.

: In step 303, a transducer layer is formed of the hygro- formed in step 302: \; on top of a scopic insulating layer. The transducer layer is formed by providing a limited amount of solution on the surface of the hygroscopic dielectric layer in sub-step 304 *: · *: and allowing said limited amount of solution to dry in sub-step 305. Typical · '· *; Ways to arrange a limited amount of solution on the surface are e.g. pipetting and mus. ···. tesuihkutus. The solution from which the modifier layer is formed may contain surfactants that affect how the solution behaves in this process.

Drying of the converter layer in sub-step 305 means that the solvent evaporates and consequently the converter layer shrinks. When the converter layer is a circular spot, there is a ha, ·! 30 shrinkage, which is in the order of 4 to 12 percent of the area of the spot. The thicker the solution layer, the stronger the shrinkage. The thickness of the finished, dried converter layer is typically 100-5000 nm. The subject is discussed in detail in LF Francis, AV McCormick, DM Vaessen & JA Payne, "Measurement and Development of Stress in Polymer Coatings", Journal of Materials Science, 37, 4717-4731 (2002). .

116704 8

According to the present invention, it is not necessary to perform steps 301-305 in any atmosphere, especially in a controlled environment. Normal room air conditions are sufficient. Contrary to many previously held beliefs, impurities and moisture, which inevitably become deposited on polymer layers in an uncontrolled atmosphere, do not degrade the performance of the formed organic thin-film device; on the contrary, they would appear to have a significant positive effect on certain measurable features of the device.

Shrinkage of the transducer layer 203 in the horizontal direction causes a horizontal mechanical force that pulls the transducer layer 202 and thus also the surface of the active layer 10 201. With the transducer layer having the shape of a round spot, the driving force acts in the radial directions of the round spot. When the transducer layer is shaped as a line on the surface of the transducer layer, the driving force is directed substantially perpendicular to the direction of the line. On the surface of the active layer, the pulling force causes the molecules of the altered active layer portion 204 to orient to some extent along the force 15. Interlayer adhesion properties are important; the better the adhesion between the layers 201 and 202 on the one hand and the layers 202 and 203 on the other hand, the more strongly a portion of the horizontal pulling force is transmitted to the active layer 201.

Fig. 4 is a schematic line drawing of an image taken from the surface of an altered ak-20 seal layer under an optical microscope using a cross-polar. i i escorts. The described sample was prepared by first making the: V layer polymer structure as shown in Figures 2 and 3 and subsequently removing the transducer and intermediary layers, · whereby the surface of the active layer was exposed. The substantially circular pattern 401 hits; · I at the same position as the upper surface of the changed active layer portion 204; in other words, i '' *; 25 is that part of the surface of the active layer which was directly beneath (circular dot, second) transducer layer 203 prior to removal of the transducer and mediator layer. The cross-polarized image shows a duplex pattern that indicates a change in the molecular order of the active layer material. Round Pattern * ;;; The outer ring of 401 shows a narrow belt 402 of strong birefringence.

9 ·; 30 The pattern of duplexity is similar to that observed in spherulites, which have the typical "Maltese Cross" pattern. Spherulites grow outward from the center outward *. The process described above is based on a solid, homogeneous,? Amorphous or semicrystalline polymeric film in which the molecules are rearranged. The birefringence pattern can only be due to the organized regions of the active layer polymer-35 materials. Examination of the various portions of the described sample by atomic microscopy confirms the presence of disorganized, substantially spherical unevenness in the active layer surface topography outside the clearly visible outer binocular fold, for example at partial magnification in visible portion 411. Inside the binocular ring, for example, at partial magnification, visible part 412, similar granules occur but appear to be elongated in the radial direction of the circular binocular pattern. At the periphery of the strong birefringence, for example, at partial magnification in the visible part 413, there is a very strong mechanical change in the surface topography, which is seen in atomic microscopy as an arrangement of closely compressed lines.

In conclusion, cross-polarized optical microscopy images and atomic microscopy studies show that the shrinkage effect of the circular spot-shaped transducer layer during fabrication causes both molecular (crystalline) ordering and mechanical surface deformation in the active layer film. The arrangement usually has a beneficial effect on the mobility of the charge carriers 15 in the active layer. It is also important to note that if only the ordering and deformation aspects described above are sought, the requirement to use hygroscopic polymers having certain predetermined electrical conductivity and insulating properties can be dispensed with. A similar shrinkage organization effect can also be achieved by using other types of materials in the "transporter" and "transducer" layers. However, if the effort is on display. . The OFET structures of the present invention and the improved transistor function also have hygroscopicity and electrical conductivity / dielectric properties. In principle, it is possible to first use other mediator and transducer layer materials to effect rearrangement and deformation in the active layer and then remove these "pre-layers" by a suitable etching or:,: other active layer-free removal process, and then formulate the final layer. and gate electrode layers having the desired oral and electrical conductivity / insulating properties of the hygroscope.

* * · · ;;; Next, certain ionic phenomena, which also occur in Fig. 2 · '·; · 30 in the sandwich structure, and which apparently have an even greater effect on the performance of, for example, organic thin-film transistors than the above-mentioned reordering and deformation phenomena if said organic thin-film transistors have. equipped with such a layer structure.

Electrochemical processes and phenomena are generally known in the art of organic thin-film semiconductor devices. The subject is discussed, for example, in D Nilsson et al., "Bi-Stable and Dynamic Current Modulation in Electrochemical Organs", Advanced Materials 2002, 14 page 51, and Epstein, A.J. et al., "Electric Field Induced Ion Leveraged Metal Insulator Transition in Conducting Polymer Based Field Effect Devices," Current Applied Physics Vol. 2, Issue 4, August 2002, p. 339-343.The mode of operation of the electrochemical FETs described therein differs from that of the 5 conventional FETs. According to the publications cited, the electrochemical transistor is of the so-called "always on" type where the gate voltage is only used to lower or shut off the source-drain current that would otherwise flow freely. The active layer of a conventional electrochemical FET consists of a highly doped conductive polymer in order to obtain the highest achievable conductivity of the channel. Other similar structures are organic FET sensors, where exposure of the channel to the environment causes chemical oxidation or reduction of the semiconductor polymer. The lattice dielectric material of such known devices has used conventional dielectric material, and otherwise such organic FET sensors have behaved like conventional FETs. Another prior art publication on electrochemical FETs is V. Rani & K.S.V. Santhanam: "Polycarbazole Based Electrochemical Transistor", J. Solid State Electrochem., 2:99 (1998). The mode of operation of prior art electrochemical FETs depends on the "natural" redox state of the polymer used.

According to the present invention, modulating the current through the active layer with the voltage applied to the converter layer can greatly improve the electrical; chemical processes and other ionic effects. In the transistor sense, this: v 'means that electrochemical processes and other ionic effects improve the modulation of the source de-drain current at the gate voltage. At the time of this writing there is no exact "". It will be appreciated that which one is of relatively greater importance in the electrochemical pro- | These processes, or ionic effects, but as both result from the selection of certain materials and process steps, are within the scope of the invention and will be further described below.

Electrochemical processes and ionic movement can occur in the polymer when '·' ··. salts or ions are present and the following two conditions are met:

• I

; '·, · 30 - an electrolyte is present for moving ions ...,: - there is an electric current producing electric charges (electrons).

: ': The electrochemical processes are fully reversible and the equilibrium state is reached within a certain time, which depends on the electric field of the polymer and the concentrations of the various specifics. The electrochemical process in an organic semiconductor can generally be described by 116704 11 polymer + C + A '-> polymers' + C + + e' (1) where "polymer" is a conjugated polymer, C is a cation, A is an anion, e is an electron and the plus and minus signs indicate electrical charge. Formula (1) means that the salt dissociates into an anion and a cation in the presence of moisture, the anion oxidizes the polymer chain of po-5 and the cation and electron remain free. The conjugated polymer remains in the oxidized state, which typically means that it becomes more conductive. The cation either gets trapped in the material or moves under the influence of a free electric field in the structure.

Consider, by way of example, electrochemical processes and other ionic phenomena in RR-10 P3HT (regioregular poly (3-hexylthiophene), a polymeric semiconductor, and in PEDOT (poly (2,3-dihydrothieno- [3,4-b] - 1,4-dioxin) which is a conductive polymer Depending on the naming standard used, PEDOT is also known as poly (dihydrotienodioxin) or polyethylene dioxide thiophene. RR-P3HT should not be confused with regiorandom type poly (3-hexylthiophene) On the other hand, for the purposes of the present invention, all regioregular poly (alkylthiophene) are not believed to function in the same way, so for generalization the term RR-PAT, regioregular poly (alkylthiophene), PEDOT is used in the highly oxidized state in aqueous dispersion. in combination with a negatively charged second polymer, typically PSS (poly,, 20 (styrene sulfonate)). as a conductor, irrespective of minor changes in the material's redox state that may result from: · electrochemical processes. The combination name PEDOT: PSS is often used. The electrochemical process has the formula PEDOrPSS '+ C + + e PEDOT + C + PSS' (2) wherein C is a cation, for example a metal ion. On the other hand, the electrochemical process significantly changes the conductivity of a semiconductor polymer, such as RR-PAT, under the influence of electric fields, since the material is inherently in the (almost) neutral: '' 'state. The formula for the process is: Λ i RR-PAT + C + A 'RR-PAT + A' + C + + e '(3) I »• _ 30 The electron appears in both formulas (2) and (3), indicating that processes '' need electric current to take place.

Assume that in the layer structure of Fig. 2, the active layer 201 is RR-P3HT, the material of the transducer layer 203 is PEDOT: PSS, and the negative layer biasing the transducer layer 203 generates an electric field. In addition, it can be assumed that due to certain other structural factors present, the active layer 201 is in contact with other electrodes (the electrode). This is the case, for example, if the layer structure of Figure 2 is part of an organic thin-film transistor 5 where a portion of the active layer 201 forms a channel between the source and the drain and the transducer layer 203 serves as a gate electrode (cf. Figure 5 illustrating device-specific electrical connections) . The hygroscopicity of the modifier (or dielectric) layer 202 means that an electrolyte is present, at least if the hygroscopic polymer is allowed to absorb moisture in it. In fact, PEDOT: PSS is also hygroscopic, which means that the electrolyte is also present in the transducer layer 203. Salts and / or ions are intentionally doped. Inadvertent impurity is also likely to occur due to residues in the polymer synthesis and contamination during processing.

By the above assumptions, the processes of formulas (2) and (3) can both occur simultaneously, but are not necessarily interdependent. A process in which the same cation would pass through the thickness of the mediator layer 202 and participate in both redox processes would potentially provide better long-term stability than fully independent processes.

. , 20 The process described by formula (2) occurs in converter layer 203. Negative »· · ;;:: bias voltage generates electrons in converter layer 203. At the same time, the process of formula: · '(3) occurs at or near the dielectric / semiconductor interface. A negative bias voltage means that the electrode or electrodes in contact with the active layer 201 remove electrons. The electrolyte in the hygroscopic isolate 202 separates the salts into negative and positive ions.

: Negative ions (anions) oxidize PHT chains and leave the active layer more conductive. The electrons on the right side of formula (3) leave the system by the aforementioned electrodes (electrode) or are trapped, for example, * * ·· ', therefore at the interface spaces in the dielectric. The cations migrate to dielectric 202 and possibly i '30 all the way to transducer layer 203 where they can participate in the formula (2). '- simultaneous reaction.

The reactions described by the above formulas (1) to (3) represent only some of the possible explanations for the organic thin film transistor of the invention having such remarkably advantageous properties. This statement should not be interpreted as trying to exclude other plausible explanations. Other ionic phenomena that are expected to have an effect are e.g. direct ion movement (drifting and diffusion); and semiconductor doping and dissociation of a polar solvent (such as water, ethanol, methanol, isopropanol, or a mixture thereof). The latter phenomenon gives rise to charged spe- cies, which can dip the semiconductor. In the case of water, the charged specificities are H + and / or OH 'ions. The process involving dissociation of the polar solvent should be pH sensitive.

If there are two electrodes in contact with the active layer 201 forming a source-sink pair (cf. the description in Figure 5 below), and if a sink voltage is used, the moving charges of the active layer 201 are also carried between the two electrodes in the active layer. This creates a channel for the active layer 201. 10 Swiping the drain voltage from zero to a value other than zero will eventually cause a cut-off either at source or sink contact, which should appear in an ideal I / V graph (i.e. appear as saturation of channel current at opening voltage). Specifically, if the active layer is of p-type semiconductor material and the gate electrode (converter 203) has a negative bias when sweeping the throat voltage from zero to a negative value, the trapping electrode is cut at the voltage determined by the hi voltage and threshold voltage. The current flowing through the channel has a purely electronic character and is therefore very fast. In other words, it should not place any time limits on the applicability of such a device. However, the ionic processes described above are based on the dissociation of salts and the movement of charged specificities of the io-20s. This is a slow process and can:. $ limits the modulation frequency, i.e.. the frequency at which certain changes ·· '·,' can be detected in the device in response to changed operating conditions.

. ,,: 'When testing various solvents that could be absorbed into the hygroscopic layer (s) of the structure, it has been found that solvents with natural-IV polarity of the molecules significantly promote ionic effects. Such solvents include: "water, ethanol, and methanol, for example. On the other hand, non-polar solvents, such as anhydrous p-xylene, do not appear to produce similar enhanced ionic effects.

• ;;; The following description of the rather abstract level will be taken further and one example of an organic thin-film transistor will be considered. Figures 5 and 30 show a top-gate thin film transistor structure according to an embodiment of the invention. Figure 5 is a cross-sectional view and Figure 6 is a top view of the structure. The relative dimensions shown in the figure are not real but are mainly selected for graphical clarity. In principle, the structure resembles the structure shown in Figure 1: it has a non-conductive substrate 501, 35 conductive source and sink electrode 502 and 503 on the surface of substrate 501, an active layer 504 connecting the source and sink electrode 502 and 503, a gate electrode 506 on said gate insulation 505. The material of substrate 501 is glass or a passive non-conductive polymer such as PET (polyethylene terephthalate) or P1 (polyimide). The source and sink electrodes 502 and 503 are made of a thin metal film, for example gold, silver or aluminum, or conductive polymers such as doped PAN (polyaniline). In general, any material that provides a substantially ohmic contact with a semiconductor material can be used.

The active layer 504 consists of a semiconductor conjugated polymer such as RR-P3HT. More generally, it can be defined that the material of the active layer 504 is of a group of 10 semiconductor polymers comprising at least poly (alkylthiophene) t and poly (fluorene-cationiophene) t, without excluding other semiconductor polymers. It is possible that one of the important prerequisites for a semiconductor polymer is the low ionization potential, which allows for easy oxidation (= doping) with charged ions. On the other hand, it has been found that regiorandom-type PHT does not give as favorable results, although it has the same ionization potential as RR-PHT. One reason why regiorandom-type PHT does not seem to work may be that its conductivity is very low and thus the currents measured in the organic thin-film transistor based on the regiorandom-type PHT are approximately in the order of leakage currents (most likely due to ion drift). Regioregular poly (alkylthiophenes) with longer side chains: ·, like RR-PHT, behave similarly to RR-PHT, but have less saturation and modulation, which is well in line with its established knowledge with regioregular poly (alkylthiophene) having longer side chains having lower conductivity than RR-PHT.

: * * ': 25 Unlike prior art organic thin-film transistors, the gate electrode 505 is made of a hygroscopic polymer such as PVP (polyvinylphenol). Other hygroscopic polymers may also be used as long as the dielectric constant of the material is sufficiently high. polyvinyl alcohol- '···, holi. Regarding the material of the gate electrode 506, it would in principle be possible to make the gate electrode 506 of metal, as well as the source and sink electrodes. However, the conductive polymer is the most suitable material for the gate electrode 506 if it is to maintain the full organic nature of the structure with processing advantages. The primary,,: candidate for such a conductive polymer is PEDOTiPSS. One additional benefit is that. the gate electrode may serve as an additional moisture reservoir to promote phenomena otherwise associated with the hygroscopicity of the gate insulation 505.

116704 15

The hygroscopic properties of the gate insulation 505 (and possibly also the gate electrode 506), the presence of salts and ions, electrochemical processes initiated by the gate voltage and other ionic effects, and the horizontal forces caused by the shrinkage of the gate electrode part 507.

The choice of materials is not only a matter of electrical conductivity but also of solvent compatibility. Preferred solvents for RR-P3HT are e.g. chloroform (i.e., trichloromethane or methyl trichloride) and xylene. The hygro-10 scopic polymer solvent of the lattice insulation should not dissolve in the active layer; good candidates for such solvents are alcohols such as 2-propanol as well as ethyl acetate and acetone. The organic gate electrode may preferably be formed from an aqueous dispersion. One known commercially available 1.3% by weight PEDOT: PSS dispersion is under the trade name Baytron P, a registered trademark of H.C.Starck GmbH.

It is worth looking at the physical dimensions of the structure a bit. The active layer 504 has a thickness of 5 to 100 nanometers, most preferably 10 to 100 nanometers. According to the invention, the conjugated polymer material of the active layer 504 need not be refined, which also limits the usable thickness of the active layer: at thicknesses greater than 100 nanometers, performance is impaired due to the bulk properties of the film. The hygroscopic gate insulation 505 has a thickness of 300-2000 nm and the gate electrode 506 has a thickness of 100-5000 nanometers. Source and throat. The length L of the channel region between the electrodes 502 and 503 is in the order of tens of micrometers, and the channel width W is typically in the order of millimeters. Experiment 25 has produced satisfactory results with at least L values of 10-400 micrometres and W 1-; **: 100 millimeters. Longer W values are most easily achieved by the use of a finger structure. Said exemplary values are not to be construed as limiting the applicability of the invention to: L and W values within said limits. outside.

Other layers may be present in the structure, particularly over the layers shown herein, although not shown in Figure 5. If the purpose is to expose the thin-film transistor device to environmental conditions and to benefit from changes in its operation caused by environmental conditions, then any * 'outer protective or decorative layers should be impermeable to at least one polar solvent. If the structure is hermetically covered with a barrier layer 35, care must be taken to ensure that the moisture in the polar solvent 116704 16 is absorbed into the structure prior to the hermetically sealing coating step.

Fig. 7 shows certain 1-V curves of the actual test apparatus of Figures 5 and 6 with a PET substrate, PANI source and throat electrodes, RR-5 P3HT active layer, PVP gate insulation, and PEDOT: PSS gate electrode. The channel length in said actual test apparatus was 20 micrometers and the channel width W was 7.2 millimeters. Figure 7 shows the source-throat voltage as the horizontal axis and the measured throat current as the vertical axis. The different curves represent different gate voltages Vg such that 701 Vg = -0.4 volts, curve 702 Vg = -0.2 volts, curve 703 Vg = -0.0 volts, 10 curves 704 Vg = +0.2 volts, and with a curve of 705 Vg = +0.4 volts. The curves in Figure 7 show that the organic thin film transistor according to the embodiment of the invention is capable of high current modulation as well as control of a relatively large drain current (lattice) at voltages substantially lower than typical values of 20-30 volts known from prior art devices. The ability to operate at low voltages 15 is extremely advantageous because of the ease of application and use of low voltages in practical applications and because the risk of electrical breakdown is reduced, even if the dielectric properties of appropriate dielectric materials are diminished, for example by environmental conditions.

The opening voltage corresponding to the gate voltage passing through the semiconductor layer. . 20 spring current starts to increase due to the gate voltage, is about 0.0 ... 0.5 volts. Nk.

: The subthreshold swing is less than 1 volts / decade and the ON / OFF ratio is 100-1000. For example, in S.M. Sze: "Physics of Semiconductor Devices", 2nd ed., John Willy & Son, New York 1981, describes standard techniques that can be applied to assess the mobility of reservation carriers that appear to be class; ': 25 boil from one to a few hundred cm2 / Vs.

Estimated mobility values for booking carriers are significantly higher than prior art values, down to non-physicality. Typical intrinsic mobility values for polymers are in the range of 10'5-10'2 cm2 / Vs, depending on the coating methods and the purity of the material. In the article C.D. Sheraw et al., "Or -; '. Tj 30 ganic Thin-Film Transistor-Driven Polymer-Dispersed Liquid Crystal Displays on ....: Flexible Polymeric Substrates," Applied Physics Letters, vol. 80, no. 6, February 2002, it is reported that the largest charge carrier mobility for organic '* semiconductors is in the order of 0.1-1 cm 2 / Vs for small molecules or oligomers.

In another article by Sirringhaus et al., "Two-Dimensional Charge Transport in Self-35 Organized, High-Mobility Conjugated Polymers", Nature 401, p. 685-688 (1999), discloses the best achievable 11670417 for intrinsically conductive polymers of 0.1 cm 2 / V s obtained with highly oriented poly (3-hexylthiophene). It is known that high mobility values can also be achieved by increasing the bulk (intrinsic) conductivity of a semiconductor material, but high intrinsic conductivity typically implies poor current modulation and current saturation.

There is ample evidence of the particular importance of the gate insulation, as well as the hygroscopicity of the gate electrode, for the measurement results described above. First, it has been found that when an organic thin-film transistor of the kind described above is introduced from room air to either intentionally dried air or a controlled nitrogen-containing environment, many of the beneficial phenomena disappear: no current modulation, no saturation of 10V curves. These advantageous phenomena return when the device is brought back into the room air. Secondly, if the polymeric gate electrode and the original gate insulation are etched and replaced with a new gate insulator and a metallic gate electrode, the advantageously high current modulation property initially observed, even if still showing the orderly phenomena of the dual refractive patterns, is significantly reduced. A related observation is that if the gate electrode was inkjet printed and not pipetted into a circular spot, little, if any, duplexing is observed, although the phenomena of high current modulation and low control voltage remain. Third, the estimated mobility values of charge carriers are by far the highest in structures where both the gate insulation and the gate electrode are hygroscopic. However, it should be noted that standard methods for assessing the mobility of booking carriers! Do not account for any ionic or electrochemical phenomena; the estimated values above only qualitatively illustrate the better L "of the equipment (compared to prior art organic thin-film transistors).

i 1 »» # 25 The fourth proof is the observed temperature dependence of the current modulation effect: low '; Temperatures known to interfere with ion movement can also be shown to reduce current modulation in an organic thin-film transistor according to one embodiment of the invention. Fifth, if the first I-V- '> measurement is made with a positive gate voltage of +0.5 volts, the curve 801 of Figure 8 is obtained. The curve; * 30 801 gives the highest current values at a drainage voltage of -0.5 ... -1.0 volts. Curves 802 and V ··· 803 represent the following measurements at gate voltages of 0.0 V and -0.5 V. The curve 801: · · i "curve" would indicate some sort of initial order of ions naturally occurring in the device ,; behavior.

Just measuring the conductivity of the RR-P3HT layer before and after installing the dielectric 35 PVP layer on it gives results that are consistent with other considerations. The conductivity of RR-P3HT increases directly with the installation of PVP 18,16704, suggesting the presence of impurity specificities in PVP that cause the mixing of RR-P3HT. The conductivity can be reduced by vacuum-heat treatment of the sample but does not achieve the original conductivity of the exposed RR-P3HT film. From the values measured after the PVP layer is installed, the conductivity is further increased when the PEDOT: PSS layer is applied over the PVP to form the gate electrode. Without the voltage applied to the PEDOT: PSS layer, the OFF state conductivity is measured at about 10'4S / cm. In the presence of a gate voltage, the measured conductivity is in the order of 10'2 S / cm.

It has been found that under wet conditions, a leakage current also occurs through a PVP layer overlaid with a PEDOT: PSS layer. Such leakage current sets an extremely low limit for the leakage currents of the organic thin-film transistor of the invention. The conductivity of the PVP layer was measured in a plate capacitor arrangement with one gold plate and one PEDOT: PSS plate and a dielectric PVP dielectric between them. The measurement gives a conductivity of about 10'11 ... 10'12 S / cm in room air and a significant-15 low conductivity in a dry nitrogen gas environment. These observations also support the above explanations based on moisture-assisted ion mobility and electrochemical effects.

Another observed feature, most probably related to non-purely electrical phenomena, is the modest frequency tolerance of the organic thin-film transistor device according to an embodiment of the invention. Fig. 9 shows the measurement results of an arrangement in which a OFET transistor with a PVP gate electrode

:.: Voltage series 0.0 V, -1.0 V, 0.0 V, -1.0 V, 0.0 V, +0.5 V, 0.0 V, -1.0 V and 0 , 0V

so that the gate voltage remained constant for 60 seconds at each stage of the series. * ί The source-drain voltage was 1.0 V. In Figure 9, the horizontal axis is the time in seconds and the vertical axis is the drain current in amperes. It is easy to see from the rounded corners of the curve 901 that after each change in the gate voltage it took several tens of seconds before the drainage current stabilized. By way of comparison, Figure 10 shows the results of a similar arrangement using a non-hygroscopic polystyrene gate insulation. This time, the source-drain voltage was 10.0 V and the series of gate voltage values was'; * '30 0.0V, -10.0V, 0.0V, -10.0V, 0.0V, +5.0V, 0.0V, -10.0V and 0.0 A. The curve 1001 is substantially rectangular and indicates much faster drainage current settling. However, it should be noted that up to ten times the gate and throat. voltage values measured in the latter case (which does not use the hygroscopic lattice insulation of the band according to the invention) remain one decade lower than in the case of Figure 9.

116704 19

The fact that the current modulation of the organic thin-film transistor according to the invention exhibits significant sensitivity to ambient humidity leads to the idea that one possible practical application of the invention could be a humidity sensor. Fig. 11 schematically illustrates a device in which the OFET unit 1101 is coupled to a bias circuit 5 1102, an operating voltage circuit 1103, and a detector circuit 1104. The OFET unit 1101 comprises two series-connected organic thin-film transistors 1111 and 1112 of The 1112 drain is connected to a negative operating voltage. The gate and source of the lower transistor 1112 are coupled together to the drain of the upper transistor 1111 10, which is also coupled to the detector circuit 1104. The biasing circuit 1102 is coupled to the gate of the upper transistor 1111.

The biasing circuit 1102 is arranged to supply a slowly oscillating bias voltage to the gate of the upper transistor 1111. Given the known shape and performance of the organic thin-film transistors of the invention, the time constant of the slowly oscillating bias 15 is typically in the order of several seconds or tens of seconds, and oscillates between voltages relatively close to zero, for example 0.0 volts and +0.5 volts. or between 0.0 volts and -0.5 volts. The detector circuit 1104 includes a peak-to-peak detector arranged to measure the maximum detectable amplitude of the oscillating voltage at the point between transistors 1111 and 1112. If the OFET unit 1101 is in a very dry environment, the current modulation capability of the transistors 1111 and 1112 is low and hence the output voltage amplitude measured in the detector circuit 1104 is small. On the other hand, if the OFET unit is exposed to humidity levels occurring in normal room air, the transistors 1111 and 1112 exhibit a strong current modulation capability, which causes relatively large oscillations at the output voltage. It is easy to implement il-: * a digital table of maize circuit 1104 that plots each detected output voltage-; the amplitude of the tea to a given moisture value estimate.

The exemplary embodiments set forth above are not to be construed as being the only way to put the invention into practice. For example, in the exemplary description of the 30 OFET transistors of the invention, only the so-called top-gate structure * · V · was discussed. just one of the known thin-film transistor infrastructures.

; * ·: Functional enhancement based on ionic effects of an organic thin film transistor device; Other types of structures may also be used. For example, a transistor structure is known in which the gate electrode is at the bottom of the gate dielectric and the active layer al-35a1a. Source and sink electrodes are uppermost. If such a structure is formed such that the gate is insulated with a hygroscopic polymer which is exposed to ambient humidity, it may function substantially as the top-gate structures described above. One way to ensure the environmental exposure of the gate insulation is to make the active layer and source and sink electrode small enough to allow moisture to enter the gate insulation around the active layer and the source and sink electrode. Another possibility is to make the active layer 5 and the source and drain electrode mesh-like so that moisture can penetrate through the holes in the mesh to contact the gate insulation.

The top-gate structure can be modified from the model shown in Figure 5 by positioning the source and sink electrode between the active layer and the gate dielectric layer instead of being positioned between the substrate and the active layer as in Figure 5. Experiments with such a modified structure show much less saturation 5, which could be interpreted as a less efficient cut.

Doping impurities can occur in the active layer for many reasons. First, an unpurified original solution may be used in which impurities are present. Second, a purified original solution may be used with the deliberately added dopant (s). Third, impurities can come from the adjacent dielectric layer, which may likewise be made of unpurified material or purified material to which an ionic substance (s) have been intentionally added.

Even if the hygroscopic gauze insulation layer (and possibly the hygroscopic gate electrode) is isolated from the environment below certain other layers, the improved function of the invention can be achieved by ensuring that sufficient moisture is absorbed into said hygroscopic layers (or layer) prior to construction. This is easy if the manufacturing process is careful. in a loop where moisture is naturally present, or in at least a certain amount of a controlled environment deliberately provided with moisture. The absorption of water into the hygroscopic layers can be promoted during manufacture by deliberately exposing said layers to water vapor or another solvent vapor prior to covering them with other layers. In a structure in which the hygoscopic layers are isolated from environmental influences, electrochemical and other ion-based enhancement of transistor function is, of course, *,, * independent of environmental conditions.

t ·

Claims (22)

A thin film transistor device comprising: - an organic semiconductor layer (201,504), - an emitter electrode (502) and a collector electrode (503) which are connected to each other via the organic semiconductor layer (201, 504), - a control electrode ( 203, 506), and - a dielectric layer (202, 505) between the organic semiconductor layer (201, 504) and the control electrode (203, 506), which dielectric layer (202, 505) is made of a hygroscopic polymer, characterized by that the dielectric layer (202, 505) has been arranged so that moisture absorbed in the dielectric layer (202, 505) in the form of a polar solution improves the function of the thin film transistor device by ionic effects. Thin film transistor device according to claim 1, characterized in that a portion of the dielectric layer (202, 505) is directly exposed to the ambient moisture. Thin film transistor device according to claim 1 or 2, characterized in that the control electrode (203, 506) is made of a hygroscopic polymer and is exposed to the moisture of the environment. Thin film transistor device according to claim 2 or 3, characterized by. . that it comprises: ;; - a substrate (501) which does not conduct electrical current, - on the surface of said substrate (501) electrically conductive sample forming the emitter (502) and the collector electrode (503), - an organic semiconductor layer (201, 504), which covers part of the emitter electrode; (502), a portion of the collector electrode (503), and a portion of the surface of said substrate: (501) between the emitter and collector electrode, - an insulating guide layer (202, 505) made of a hygroscopic polymer; which layer covers said organic semiconductor layer (201,504) at the site where one, * · *. a portion of the emitter electrode (502), a portion of the collector electrode (503), and a portion of the surface of said substrate (501) between the emitter and collector electrode are located; and - a control electrode layer (203, 506), which covers a part of said insulating control layer (202, 505) at the site where part of the emitter electrode (502), part of carbon. The lead electrode (503), and a portion of the surface of said substrate (501) between the emitter and collector electrode is located. 116704 Thin film transistor device according to claim 4, characterized in that the thickness of said organic semiconductor layer (201, 504) is 5-500 nanometers, the thickness of said insulating control layer (202, 505) is 300-2000 nanometers, and the thickness of said control electrode layer (203, 506) is 100-5000 nanometers. Thin film transistor device according to claim 4 or 5, characterized in that the material for said organic semiconductor layer (201, 504) is of the group of poly (alkylthiophene) and poly (fluorene-coctiophene) group; the material for said insulating guide layer (202, 505) is from the polyvinylphenol and polyvinyl alcohol group; and the material for said guide electrode layer (203, 506) is a combination of polyethenedioxitiophene and poly (styrene sulfonate). Thin film transistor device according to claim 6, characterized in that the material for said organic semiconductor layer (201, 504) is poly (3-hexylthiophene) of the regular type and that the material for said insulating control layer (202, 505) is polyvinylphenol. Thin film transistor device according to claim 6, characterized in that either the material for said organic semiconductor layer (201, 504) or the material for said dielectric layer (202, 505) is non-pure or alternatively both materials are non-pure. : 9. Thin film transistor device according to claim 6, characterized in that the material of said organic semiconductor layer (201, 504) or the material of said dielectric layer (202, 505) is purified polymer, which intentionally has · :. added ion or processing agent or alternatively, both materials are purified polymers of said type. : ···. Thin film transistor device according to one of the preceding claims, characterized in that the surface located against the dielectric layer (202, 505) of the organic semiconductor layer (201, 504) has a region (204, 401, 507) within which one can discern a rearrangement of molecules and mechanical change of the surface shape at the site of the control electrode (203, 506). Thin film transistor device according to claim 1, characterized in that it comprises absorbed moisture in the dielectric layer (202, 505) as well as a closure arrangement for tightly separating the dielectric layer (202, 505) from the thin layer. *; the environment of the film transistor device. 116704 Electronic measuring circuit, characterized in that it comprises: - a thin film transistor device (1101) according to claim 1, which is subjected to the influence of the environment, - a biasing circuit (1102) for providing a bias voltage for a thin film transistor (1111) which is in said thin film transistor device (1101), - an operating voltage circuit (1103) for providing an operating voltage for said thin film transistor device (1101), and in the current modulation capability of said thin film transistor device (1101) due to changed ambient conditions. Electronic measuring circuit according to claim 12, characterized in that - the thin-film transistor device (1101) comprises a first organic thin-film transistor (1111) and a second organic thin-film transistor (1112), which are connected in series in such a way that the collector electrode of the first organic the thin film transistor (1111) has been coupled to the emitter electrode and the control electrode of the second organic thin film transistor (1112); ) has been coupled to supply an operating voltage across:,. the series connection formed by said first organic thin film transistor (1111) and J ·, 'said second organic thin film transistor (1112), and'; - said detector circuit (1104) has been coupled to detect potential changes at a point between the first organic thin film transistor (1111) and the second organic thin film transistor (1112) forming said series circuit. Electronic measuring circuit according to claim 12 or 13, characterized in that said biasing circuit (1102) is arranged to supply an oscillating bias voltage. to the thin film transistor device (1101) and to said detector circuit. (1104) has been arranged to detect a change in the peak voltage value in the measuring point within the thin film transistor device (1101). A method of manufacturing a thin film transistor device, comprising the steps of:: v - an organic semiconductor layer is formed (301) to interconnect an emitter and collector electrode pairs, 35. a dielectric layer is formed (302) from a hygroscopic polymer to cover a portion of the organic semiconductor layer, and a control electrode is formed (302) to cover a portion of the dielectric layer and is superposed relative to each other. a channel area between said emitter electrode and said collector electrode; characterized in that: 5. In the process, the dielectric layer has been arranged to absorb moisture in the form of a polar solution to improve the function of the thin film transistor device by ionic effects. 16. A method according to claim 15, characterized in that when the dielectric layer is absorbed to absorb moisture, a part of the dielectric layer is exposed to the environment in the finished thin film transistor device. Method according to claim 15 or 16, characterized in that the step in which a control electrode is formed (303) comprises steps in which: - a certain amount of polymer solution is applied (304) to a part of the dielectric layer, and 15. said amount of polymer solution allowed (305) to dry and shrink, whereby a force in the direction of the plane of the dielectric layer rises, which force mechanically alters the surface of the organic semiconductor layer. Method according to any of claims 15-17, characterized in that said steps (301,302, 303, 304, 305) are carried out in a room environment. I · .V 20 Method according to any one of claims 15-18, characterized in that the etheric stone of one of said steps (301,302, 303, 304) comprises an application of printing or printing technology together with the polymer solution for forming the layer. . * »· * ·» · • v. 20. A method according to claim 15, characterized in that it is delimited. The electric layer absorbs moisture, a portion of the dielectric layer is left exposed to moisture at the stage of manufacture of the thin film transistor device and later insulated. . the dielectric layer is dense from the surroundings. 21. A method according to claim 15, characterized in that either at the stage in which the organic semiconductor layer is formed (301) or at the stage in which the di-electric layer is formed (302), or at both stages. , is used as a layer material of non-pure polymer. 1 1 6704 Method according to Claim 15, characterized in that either at the stage in which the organic semiconductor layer is formed (301) or at the stage in which the dielectric layer is formed (302), or at both stages, the layer material is purified. polymer to which has been intentionally added ionic or processing agents. ♦ »'t •» t »' r t t> · · * i f I I I