(19) TZZ _¥¥_T (11) EP 2 797 133 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.: 29.10.2014 Bulletin 2014/44 H01L 51/05 (2006.01) H01L 51/10 (2006.01) H01L 51/52 (2006.01) (21) Application number: 13164959.2 (22) Date of filing: 23.04.2013 (84) Designated Contracting States: • Kleemann, Hans AL AT BE BG CH CY CZ DE DK EE ES FI FR GB 01187 Dresden (DE) GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO • Lüssem, Björn PL PT RO RS SE SI SK SM TR 01127 Dresden (DE) Designated Extension States: •Leo,Karl BA ME 01219 Dresden (DE) (71) Applicants: (74) Representative: Bittner, Thomas L. • Novaled GmbH Boehmert & Boehmert 01307 Dresden (DE) Anwaltspartnerschaft mbB • Technische Universität Dresden Patentanwälte Rechtsanwälte 01062 Dresden (DE) Pettenkoferstrasse 20-22 80336 München (DE) (72) Inventors: •Günther,Alrun 01159 Dresden (DE) (54) A method for producing an organic field effect transistor and an organic field effect transistor (57) The present disclosure relates to a method for producing an organic field effect transistor, the method comprising steps of providing a gate electrode (1) and a gate insulator (2) assigned to the gate electrode (1) for electrical insulation on a substrate, depositing a first or- ganic semiconducting layer (3) on the gate insulator (2), generating a first electrode (4) and an electrode insulator (5) assigned to the first electrode (4) for electrical insu- lation, depositing a second organic semiconducting layer (6) on the first organic semiconducting layer (3) and the electrode insulator (5), and generating a second elec- trode (7), wherein the method further comprises at least one of the following steps generating a first doping ma- terial layer (13) on the first organic semiconducting layer (3) prior to generating the first electrode (4) and the elec- trode insulator (5) such that the first electrode (4) with the electrode insulator (5) are generated at least partially on the first doping material layer (13), and generating a second doping material layer (14) on the second organic semiconducting layer (6) prior to generating the second electrode (7) such that the second electrode (7) is gen- erated at least partially on the second doping material layer (14). Furthermore, an organic field effect transistor is provided. EP 2 797 133 A1 Printed by Jouve, 75001 PARIS (FR) 1 EP 2 797 133 A1 2 Description porting layer are arranged on the semiconducting layer. Further, the transistor comprises an emitting layer and a [0001] The invention relates to a method for producing drain electrode. anorganic field effect transistorand an organic field effect [0007] There is a need to provide a transistor design transistor. 5 which allows high current densities in the device and which can be produced in an easy and controllable man- Background of the invention ner. [0002] For a realization of flexible and electronic com- Summary of the invention ponents based on organic semiconducting elements it is 10 necessary to develop capable and robust organic tran- [0008] It is the object of the invention to provide a meth- sistors. A promising approach is provided by vertical or- od for producing an organic field effect transistor and an ganic field effect transistors (VOFETs). organic field effect transistor, wherein the organic field [0003] A VOFET (as field effect transistors in general) effect transistor has a high current density. is formed with three electrodes, namely a gate electrode, 15 [0009] This object is solved by the method according a source electrode and a drain electrode. In a VOFET, to the independent claim 1 and the organic field effect the source electrode and the drain electrode are con- transistor according to the independent claim 12. Advan- nected with each other by an organic semiconductor. The tageous embodiments of the invention are the subject of gate electrode is separated from the source electrode dependent claims. and the drain electrode by an insulator. The elements of 20 [0010] According to one aspect of the invention, a the VOFET are formed as a stack on a substrate, wherein method for producing an organic field effect transistor is the stack has one of the following sequences of layers: provided. The method comprises steps of providing a substrate / gate electrode / insulator / source electrode / gate electrode and a gate insulator assigned to the gate drain electrode or substrate / drain electrode / source electrode for electrical insulation on a substrate, depos- electrode / insulator / gate electrode. The organic semi- 25 iting a first organic semiconducting layer on the gate in- conductor is always arranged between the source elec- sulator, generating a first electrode and an electrode in- trode and the drain electrode. Additionally, it can be ar- sulator assigned to the first electrode for electrical insu- ranged between the insulator and the source electrode. lation, depositing a second organic semiconducting layer Two methods are known for producing a VOFET: self- on the first organic semiconducting layer and the elec- organization of the materials and technical structuring, 30 trode insulator, and generating a second electrode. Fur- for example with a shadow mask. ther, the method comprises at least one of the following [0004] The document WO 2010/113163 A1 discloses steps: generating a first doping material layer on the first a vertical organic field effect transistor and a method for organic semiconducting layer prior to generating the first producing the same. The transistor comprises a pat- electrode and the electrode insulator such that the first terned electrode structure which is enclosed between a 35 electrode with the electrode insulator are generated at dielectriclayer and an activeelement. The activeelement least partially on the first doping material layer, and gen- is either an organic semiconductor or an amorphous erating a second doping material layer on the second semiconductor. The electrode structure is patterned by organic semiconducting layer prior to generating the sec- using a block copolymer material as a patterning mask. ond electrode such that the second electrode is gener- Hereby, the thickness of the patterned layer and lateral 40 ated at least partially on the second doping material layer. feature size can be selected. [0011] According to another aspect of the invention, [0005] A method for forming an organic device having an organic field effect transistor is provided, comprising a patterned conductive layer is disclosed in document a first electrode and a second electrode, the electrodes WO 2011/139774. The method comprises the steps of providing a source electrode and a drain electrode, a depositing an organic layer on a substrate and coating 45 gate electrode, a gate insulator provided between the the organic layer with a photoresist solution to form a gate electrode and the first electrode, an electrode insu- photo-patternable layer. The photoresist solution in- lator providedbetween thefirst and the secondelectrode, cludes a fluorinated photoresist material and a fluorinated a first organic semiconducting layer provided between solvent. Selected portions of the photo-patternable layer the gate insulator and the first electrode, a second or- are radiated to form a pattern. A conductive layer is coat- 50 ganic semiconducting layer provided between the first ed over the organic layer. A portion of the conductive organic semiconducting layer and the second electrode, layer is removed to form a patterned conductive layer. and at least one of the following layers: a first doping [0006] K. Nakamura et al., Applied Physics Letters Vol. material layer which is provided between the first elec- 89, page 103525 (2006) discloses an organic light emit- trode and the first organic semiconducting layer and ting transistor. A gate electrode is arranged on a sub- 55 which is at least partially in direct contact with the first strate and covered by a gate insulating layer. A semicon- electrode, and a second doping material layer which is ducting layer is coated on the gate insulating layer. A provided between the second electrode and the second source electrode, an insulating layer, and a hole trans- organic semiconducting layer and which is at least par- 2 3 EP 2 797 133 A1 4 tially in direct contact with the second electrode. The first doping material layer, respectively. and second organic semiconducting layers can be con- [0017] VOFETs in general have an asymmetric re- figured to transport charge carriers of the same type, sponse for positive and negative Drain-Source voltages namely holes and electrons. Alternatively or in addition, VSD caused by the different electrical field from the gate the first and second organic semiconducting layers can 5 electrode to the source and drain electrodes, due to the be configured to transport both carrier types, namely different distances of the source and drain electrodes to holes and electrons. the gate insulator. It was found that by using a first doping [0012] The invention refers to a vertical transistor de- material layer between the source electrode and the first sign. The first and second electrode each provides a con- semiconducting layer and / or a second doping material tact for applying a voltage to the transistor. The gate elec- 10 layer between the drain electrode and the second organic trode provides a contact for controlling the state of the semiconducting layer, respectively, it is possible to con- transistor. By the electrode insulator a parallel resistance trol the asymmetry. Preferably, the first and / or second of the transistor is reduced and the ratio between the doping material layers have a thickness of less than 5 current in an ON-state and the current in an OFF-state nm, respectively. is increased. 15 [0018] In a hole transport layer (HTL) the mobility of [0013] In an exemplary embodiment the method com- holes is larger than the mobility of electrons.