DE102007018800A1 - Electronic component i.e. organic FET, for inverter, has transistor channel with part that is controlled in boundary layer and insulator, where source-drain current between off and on conditions is controlled over dimensions by gate voltage - Google Patents

Abstract

The component has a substrate (10) that is electrically insulated by an intermediate layer of an active part of the component. A source electrode (50), drain electrode and an electrically conductive gate electrode (20) are attached to the substrate. A layer of a charge-transporting organic semiconductor is separated by a gate insulator (30) of the electrode. A part of a transistor channel is capacitively controlled in a boundary layer of the layer and the insulator, where source-drain current between off and on conditions is controlled over multiple dimensions by gate voltage.

Description

State of the art

The present invention relates to an electronic component based on organic semiconductors, in particular an organic field effect transistor (OFET). OFETs are known in various designs and on the basis of various organic semiconductors. In principle, an organic semiconductor forms a channel between drain and source, which is separated from the gate by a gate insulator. By applying a voltage to the gate electrode, the conductivity of the channel located between the drain and source electrodes at the interface to the gate insulator can be capacitively modulated. An overview of conventional OFETs can be found, for example, in "Organic Thin Film Transistors" by Colin Reese, Marc Roberts, Mang Mang Lin, and Zhenan Bao in Materials Today, pp. 20-27, September 2004 ,

Of the The present invention is based on the object, the transfer characteristic and to improve the switching behavior of OFETs.

Advantages of the invention

The electronic component based on organic semiconductors, in particular OFET, with the characterizing features of claim 1 has the Advantage of an improved switching behavior compared to conventional OFETs.

The Gate voltage allows between an "OFF state", wherein the source-drain current through the reverse current of a diode is given, and an "ON state" in which the current given by an avalanche-like breakthrough, to switch. The source-drain current can be over several orders of magnitude can be varied and it can be a very steep switching behavior than Function of the gate voltage can be achieved. The invention Electronic component based on organic semiconductors can in particular for the manufacture of circuits based on complementary Logic can be used.

By the characteristics listed in further claims are advantageous developments of the generic OFETs possible.

drawing

Of the OFET according to the invention and its advantages described in more detail with reference to the drawings. Show it:

1 : a schematic representation of an OFET according to the invention

2 : a source-drain characteristic of an OFET according to the invention in the "OFF state", ie without an applied gate voltage The diode-like behavior is clearly visible For negative voltages below V _d an avalanche-like breakthrough is shown.

3 : a schematic representation of an inventive OFET in the "ON" state

4 : A schematic representation of a vertical OFET according to the invention in the "ON" state

5 A transfer characteristic of a copper-phthalocyanine-based OFET according to the invention. The characteristic corresponds to that of a p-type field effect transistor.

6 : A transfer characteristic of a fluorinated copper phthalocyanine-based OFET according to the present invention. The characteristic corresponds to the characteristic of an n-type field effect transistor.

7 Figure 1: the area of the reverse breakdown between source and drain contact for a copper phthalocyanine based OFET according to the invention.

8th Figure 4: the reverse breakdown region between source and drain contact for a fluorinated copper phthalocyanine based OFET according to the present invention.

9 : the mobility of positive charge carriers in copper phthalocyanine single crystals as a function of temperature

embodiments

1 shows the schematic structure of an OFET according to the invention. The OFET according to the invention comprises a substrate ( 10 ). The substrate ( 10 ) is preferably electrically insulating or electrically isolated from the active part of the device by a suitable intermediate layer. Advantageously, the substrate ( 10 ) be formed mechanically flexible. An electrically conductive gate electrode ( 20 ) is on the substrate ( 10 ) applied. In principle, the gate electrode ( 20 ) the task of the substrate ( 10 ) at least partially take over. Possible materials for the gate electrode ( 20 ) are highly doped semiconductors, metals or conductive oxides such as indium tin oxide and doped zinc oxide. Other materials are known to those skilled in the art. It is particularly advantageous if the gate electrode ( 20 ) can be produced by a low-cost deposition process, for example a printing process. Other methods of preparation are known to those skilled in the art.

An electrically insulating layer ( 30 ), the gate insulator, disconnects the electrical contacts ( 50 . 60 ) and the active organic layer ( 40 ) of the electrically conductive gate electrode ( 20 ). Typical insulator materials for the gate insulator ( 30 ) are, for example, silica, alumina, tantalum oxide, polyimide, polyvinylphenol, polyvinyl alcohols, cyanopullulan, polyisobutylene, polysiloxanes, polystyrenes or polymethylmethacrylate. Likewise, the application of ferroelectric insulators is conceivable. The skilled person is familiar with other organic, inorganic and hybrid materials for use as gate insulator in field effect transistors. It is also possible to use the insulating layer ( 30 ) from more than one material or from multiple layers. In addition, the interface between the insulating layer ( 30 ) and the active organic layer ( 40 ) may be modified by suitable buffer layers or self-assembling monolayers which improve the production and / or properties of the OFET.

The active organic layer ( 40 ) is in direct contact with the gate insulator ( 20 ). The layer ( 40 ) consists of a semiconductive material, which is preferably formed crystalline. Typical molecular organic semiconductors are oligoacenes, fullerenes, phthalocyanines or their derivatives. Organic semiconductors that exhibit linear stacking of the molecules or show additional attractive forces between the molecules in addition to the pure van der Waals interaction are of particular interest: interactions between neighboring sulfur or selenium atoms. Hydrogen bonds, hybridization of π-electrons with orbitals of metal atoms or ionic and dipole-like interactions are just a few examples: In addition to organic semiconductors, the use of organic-inorganic hybrid materials for the active layer ( 40 ) conceivable. It is immediately apparent to the person skilled in the art that the deposition of the active layer ( 40 ) can be done either from the gas phase, in vacuo or from the solution. It is particularly advantageous if the active organic layer ( 40 ) is separated from the solution by a cost effective process. The person skilled in the art is familiar with further production techniques from the prior art.

The electrical contacts ( 50 . 60 ) are in contact with the active organic layer ( 40 ). Simultaneous contact of the gate insulator ( 30 ), as in 1 is possible, but not necessarily required. It is immediately apparent to the person skilled in the art that further modifications of the 1 shown structure for the production of organic field effect transistors are possible ("top-contact", "bottom-gate").

The electrical contacts ( 50 . 60 ) are designed such that they inject a charge carrier type, either p-type (holes) or n-type (electrons), into the active organic layer ( 40 ) and injection of the other charge carrier type into the active organic layer ( 40 ) suppress. It is especially necessary that the drain contact ( 60 in electron injection (or hole injection) of the source contact ( 50 ) into the active organic layer ( 40 ) for electrons (or holes) has a blocking effect. In the absence of a gate voltage, the drain-source characteristic is therefore diode-like. It may be advantageous that the material of the active organic layer ( 40 ) has a band gap of more than 1.5 eV.

An essential determinant of the injection properties of contacts with organic materials is the "interface offset." This "interface offset" is significantly influenced by the properties of the layers involved, ie, the active organic layer ( 40 ) and the electrical contacts ( 50 . 60 ), as well as the properties of the interface, for example the dipole properties, between these layers.

In particular, high work function materials such as platinum, palladium, gold, indium-tin oxide or titanium nitride can be used for hole injection. It will be readily apparent to those skilled in the art that an improvement in injection properties can be achieved through the use of suitable buffer layers. It is particularly advantageous if the charge carrier injecting contacts ( 50 . 60 ) can be produced by a cost-effective process. Methods for this are known to the person skilled in the art.

typical Contact materials for electron injection have a low Work function such as aluminum, calcium, magnesium, Cesium. Barium, alkali fluorides, alkaline earth fluorides or oxides. Other materials are the expert from the prior Technique known.

For forming a barrier contact for a charge carrier type, it may be advantageous that the active organic layer ( 40 ) has a relatively large energy gap or a large energetic distance between HOMO ("Highest occupied molecular orbital") and LUMO ("Lowest unoccupied molecular orbital"). In this way, for contacts ( 50 . 60 ) for hole injection due to alignment of the work function at the position of the valence band or HOMO level, a large barrier to electron injection due to the energetic position of the conduction band or LUMO level. A band gap or a HOMO-LUMO distance of more than 1.5 eV proves advantageous for the organic field-effect transistor according to the invention but not as absolutely necessary.

In addition, further possibilities for modifying the injection properties of the contacts ( 50 . 60 ), for example by buffer layers, in particular self-assembling monolayers. In particular, the "charge transfer doping" and dipole properties are of great importance.Another method for modifying the injection properties is doping, doping methods and suitable n- or p-type dopants are known to the person skilled in the art.

Without an applied gate voltage, ie in the "off state", the channel has a diode-like characteristic, which is advantageously operated in the reverse direction. 50 ) and drain contact ( 60 ) only a small reverse current through the active organic layer ( 40 ).

2 shows the source-drain characteristics of an OFET according to the invention in the "OFF state". The diode-like behavior is clearly visible. For negative voltages, that is in the blocking region of the diode, is showing an avalanche-like breakthrough below the breakdown voltage of V _d. The voltage value V _d is determined by the effective field strength in the active organic layer ( 40 ) certainly. By reducing the "diode length" between source ( 50 ) and drain contact ( 60 ), it is therefore possible to vary the breakdown voltage V _d .

3 schematically shows an OFET according to the invention in the "ON state." By the application of a voltage between the gate electrode (FIG. 20 ) and source electrode ( 50 ) at the interface between the gate insulator ( 30 ) and the layer of the organic semiconductor ( 40 ) in an area of the channel ( 70 ) Induces charge carriers. The length of this channel area ( 70 ) is referred to as gate length L _g . The length of the part of the channel in which no charge carriers are induced _is denoted by L _d . Is the OFET according to the invention now between source ( 50 ) and drain contact ( 60 If the "diode length" in the "OFF state" corresponds to the total channel length, ie L _g + L _d , it shortens in the "ON state""on L _d . Consequently, by the gate voltage between a reverse current between source ( 50 ) and drain contact ( 60 ) in the "OFF state" and a break-through current between source ( 50 ) and drain contact ( 60 It should be noted, however, that this is only possible with a finite source-drain voltage which is greater in magnitude than the breakdown voltage of the "shortened" source-drain diode.

4 Fig. 1 shows schematically a "vertical" OFET according to the invention in the "ON state". The names correspond to those in 2 , In contrast to the "horizontal" or "planar" arrangement in 2 , here the channel "vertical" is arranged, that is to say the total channel length (L _g + L _d ) is determined by the thickness of the layer of the organic semiconductor ( 40 ). This arrangement is advantageous to achieve short channel lengths. Since the switching behavior of the component is determined by the effective electric field strength, the necessary source-drain voltage can be reduced by shortening the channel.

It is immediately apparent to the person skilled in the art that also from in 2 and 3 deviating arrangements, in particular geometrical arrangements, consisting of at least one active organic layer ( 40 ), a gate insulator ( 30 ), Source ( 50 ), Drain ( 60 ) and gate electrode ( 20 ) such behavior through the applied gate voltage.

5 shows a transfer characteristic of a OFET based on a copper-phthalocyanine single crystal according to the invention. The device behaves as a p-type field effect transistor. At a gate voltage of about -5.5 V, it is possible to switch between the "OFF state" and the "ON state". The switching behavior is characterized by its steepness. It should be noted that the steepness is not thermodynamically limited in contrast to conventional OFETs. Furthermore, the "OFF state" is characterized by low currents, since it is based on a reverse-biased diode.

6 shows a transfer characteristic of an OFET based on a fluorinated copper-phthalocyanine single crystal according to the invention. The device behaves as an n-type field effect transistor. The device behaves as an n-type field effect transistor. At a gate voltage of about +25 V, it is possible to switch between the "OFF state" and the "ON state".

How out 5 and 6 can be seen, generic OFETs can be represented as n- or p-type transistors and therefore allow a variety of ways for the construction of complementary, logic circuits. Here, however, it should be noted that, as mentioned above, a finite source-drain voltage is a prerequisite for the observation of the transistor behavior. In particular, it is also possible to form n- and p-type transistors with the same organic semiconductor, which can simplify the production of complementary circuits. The type of transistor can be determined, for example, by the choice of source and drain contact materials.

wobei e die Elementarladung, h das Planck'sche Wirkungsquantum, Φ die Barrierenhöhe zur Ladungsträgerinjektion, B die effektive Tunnelfeldstärke, w die Schichtdicke, α₀ der Ionisierungskoeffizient und H die effektive Ionisierungsfeldstärke ist. Die Koeffizienten B, H und α₀ können aus einem Fit an die experimentellen Daten abgeschätzt werden. Des Weiteren gilt ein Zusammenhang zwischen der effektiven Ionisierungsfeldstärke H und der mittleren freien Weglänge I:

wobei E_i die Ionisierungsenergie des Materials darstellt. Die effektiven Masse der Ladungsträger m* läßt sich aus der effektiven Tunnelfeldstärke über folgende Relation abschätzen:

7 shows the range of electrical breakdown for an inventive electronic component based on single crystal copper phthalocyanine. The experimental data are represented by circles. The solid line corresponds to a fit to this data according to a simple model of charge carrier multiplication due to collisions, ie the formation of carrier avalanches. In this case, the current density J is a function of the electric field strength E:

where e is the elementary charge, h is Planck's constant, Φ is the barrier height for carrier injection, B is the effective tunnel field strength, w is the layer thickness, α _{0 is} the ionization coefficient, and H is the effective ionization field strength. The coefficients B, H and α ₀ can be estimated from a fit to the experimental data. Furthermore, there is a relationship between the effective ionization field strength H and the mean free path length I:

where E _{i represents} the ionization energy of the material. The effective mass of the charge carriers m * can be estimated from the effective tunnel field strength by the following relation:

Consequently, it is possible to determine the mobility of the charge carriers μ in the organic semiconductor as a function of the field strength E via the following relationship:

8th shows the range of electrical breakdown for an inventive electronic component based on monocrystalline fluorinated copper phthalocyanine. The experimental data are represented by squares. The solid line corresponds to a fit to this data according to the charge carrier multiplication model described above due to the formation of carrier avalanches.

9 shows the mobility of positive charge carriers in a copper-phthalocyanine single crystal as a function of temperature. The values for the mobility are determined from the breakthrough behavior, as in 7 and 8th is shown. Table 1 shows room temperature values obtained in this way for various organic materials. Table 1: Carrier mobilities at room temperature for various organic materials determined from the breakdown behavior. μ _n and μ _p represent the mobility of electrons and holes. material μ _n (cm ² / Vs) μ _p (cm ² / Vs) Copper phthalocyanine 40 52 Zinc phthalocyanine - 63 Metal-free phthalocyanine 4 3 Fluorinated copper phthalocyanine 48 - pentacene 6 10 perylene 8th 3

the One skilled in the art will readily appreciate that the invention OFET the basis for circuits with complementary Can form logic. In particular, from two inventive OFETs with n-type or p-type behavior formed inverter circuits which, in turn, be part of more complex circuits can. It should be noted in particular that how shown in Table 1, various materials both p-type and can also form n-type OFETs. Furthermore, it is immediate it can be seen that the invention OFET the form elementary part of semiconductor memory cells.

It It should be understood that the foregoing description is illustrative only for the invention. Various alternatives and modifications can be done by a professional without departing from the invention be considered. Accordingly, the present Invention is thought to contain all such alternatives, modifications and variations included within the scope of the appended claims Claims fall.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• "Organic Thin Film Transistors" by Colin Reese, Marc Roberts, Mang Mang Lin and Zhenan Bao in Materials Today, pp. 20-27, September 2004 [0001]

Claims (34)

Electronic component based on organic semiconductors, which is a substrate ( 10 ), a source electrode ( 50 ), a drain electrode ( 60 ), a gate electrode ( 20 ) and a layer of a charge-transporting organic semiconductor ( 40 ), which by a gate insulator ( 30 ) from the gate electrode ( 20 ) is spatially separated, wherein the source electrode ( 50 ), the drain electrode ( 60 ) adjacent to the layer of the organic semiconductor ( 40 ) and the gate electrode ( 20 ) adjacent to the gate insulator ( 30 ) are arranged, characterized in that by the gate electrode ( 20 ) just a part ( 70 ) of the transistor channel at the interface of the charge-transporting organic semiconductor layer ( 40 ) and the gate insulator ( 30 ) is capacitively controlled, wherein by the gate voltage, the source-drain current between an OFF state and an ON state can be controlled over several orders of magnitude. Electronic component based on organic semiconductors according to claim 1, characterized in that the OFF state on the reverse current of a diode between the source electrode ( 50 ) and drain electrode ( 60 ). Electronic component based on organic semiconductors according to one of claims 1 or 2, characterized in that the ON state on the breakdown behavior of a diode between the source electrode ( 50 ) and drain electrode ( 60 ). Electronic component based on organic semiconductors according to claim 3, characterized in that the ON state on the avalanche-like breakdown behavior of a diode between the source electrode ( 50 ) and drain electrode ( 60 ). Electronic component based on organic semiconductors according to one of Claims 1 to 4, characterized in that the source electrode ( 50 ) allows the injection of a charge carrier type and the drain electrode ( 60 ) is blocking for this type of charge carrier. Electronic component based on organic semiconductors according to one of claims 1 to 4, characterized in that the drain electrode ( 60 ) allows the injection of a charge carrier type and the source electrode ( 50 ) is blocking for this type of charge carrier. An organic semiconductor-based electronic component according to any one of claims 1 to 6, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) contains a molecular organic semiconductor. An organic semiconductor-based electronic component according to any one of claims 1 to 7, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) can transport both types of charge carriers. An organic semiconductor-based electronic component according to any one of claims 7 or 8, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) Oligoacenes, oligothiophenes, oligophenylenevinylenes, fullerenes, metallofullerenes or their derivatives. An organic semiconductor-based electronic component according to any one of claims 1 to 7, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) contains a polymeric organic semiconductor. Electronic component based on organic semiconductors according to claim 10, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) Polythiophenes, polyindenofluorenes, polyphenylenevinylenes, polyfluorenes or their co-polymers. An organic semiconductor-based electronic component according to any one of claims 1 to 7, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) contains an organic-inorganic hybrid material. An organic semiconductor-based electronic component according to any one of claims 1 to 12, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) has a band gap of more than 1.5 eV. Electronic component based on organic semiconductors according to one of claims 1 to 13, characterized in that at least the source contact ( 50 ) is modified by a buffer layer. Electronic component based on organic semiconductors according to one of claims 1 to 13, characterized in that at least the source contact ( 50 ) is modified by a self-assembling monolayer. Electronic component based on organic semiconductors according to one of Claims 1 to 13, characterized in that at least the drain contact ( 60 ) is modified by a buffer layer. Electronic component based on organic semiconductors according to one of Claims 1 to 13, characterized in that at least the drain contact ( 50 ) is modified by a self-assembling monolayer. An organic semiconductor-based electronic component according to any one of claims 1 to 17, characterized in that both the source contact ( 50 ) as well as the drain contact ( 60 ) are modified by a self-assembling monolayer. An organic semiconductor-based electronic component according to any one of claims 1 to 18, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) at least in the region of the source contact ( 50 ) is locally doped. An organic semiconductor-based electronic component according to any one of claims 1 to 18, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) at least in the region of the drain contact ( 60 ) is locally doped. An organic semiconductor-based electronic component according to any one of claims 1 to 18, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) both in the region of the source contact ( 50 ) as well as in the region of the drain contact ( 60 ) is locally doped. An electronic component based on organic semiconductors according to one of claims 1 to 21, characterized in that the gate insulator ( 30 ) is deposited from the solution. Electronic component based on organic semiconductors according to one of Claims 1 to 22, characterized in that the gate electrode ( 20 ) is deposited from the solution. Electronic component based on organic semiconductors according to one of claims 1 to 23, characterized in that the source ( 50 ) and drain contacts ( 60 ) are separated from the solution. An organic semiconductor-based electronic component according to any one of claims 1 to 24, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) is deposited from the solution. Electronic component based on organic semiconductors according to one of claims 1 to 25, characterized in that the component is mounted on a mechanically flexible substrate ( 10 ) is applied. An organic semiconductor-based electronic component according to any one of claims 1 to 26, characterized in that the substrate ( 10 ) includes a plastic. An organic semiconductor-based electronic component according to any one of claims 1 to 27, characterized in that the layer of the charge-transporting organic semiconductor ( 40 ) is formed at least partially crystalline. Electronic component based on organic Semiconductor according to one of Claims 1 to 28, characterized that the transparent field effect transistor is airtight encapsulated is. Inverter comprising a first and a second electronic component based on organic semiconductors according to one of claims 1 to 29, characterized in that the two electronic components based on organic semiconductors, the layer of the charge-transporting organic semiconductor ( 40 ) have in common. Inverter according to claim 30, characterized in that the two electronic components based on organic semiconductors, the gate insulator ( 20 ) have in common. Semiconductor memory cell with at least one electronic An organic semiconductor device according to any one of the claims 1 to 29. Circuit with at least one electronic An organic semiconductor device according to any one of the claims 1 to 29. Circuit with at least one inverter after one of claims 30 or 31.