JP2007073619A - Evaluation device and characteristics measuring method of organic semiconductor field effect transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new effective evaluation method for an organic semiconductor field effect transistor to monitor generation of channel and changes in channel conductance in non-contact manner. <P>SOLUTION: A voltage is applied between the gate and source-drain of an organic semiconductor field effect transistor. Light enters a channel formation region in an organics layer positioned between the source and the drain where a channel layer is to be formed. A high-order harmonic light is detected as emitted from the channel formation region which the light has entered. The conductance and/or field distribution in the channel formation region is measured by the intensity of the detected high-order harmonic light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an evaluation apparatus and characteristic measurement method for an organic semiconductor field effect transistor.

  A transistor using an organic material is manufactured by depositing or coating an organic material on a substrate. Since organic substances are bonded mainly by intermolecular forces (Van der Waals forces), they are more flexible than atomic bonds such as Si crystals. In addition, if a plastic substrate is used, the thickness can be reduced as compared with a Si substrate or a glass substrate.

  For this reason, it is possible to produce a light, thin and bent electronic device by using a transistor using an organic material. In addition, there is an advantage that the cost of materials and the like is low. That is, by using a transistor including an organic substance, an element having flexibility in shape can be manufactured at low cost.

  As an example of the element using this organic substance, for example, an organic semiconductor field effect transistor (organic semiconductor FET: Field Effect Transistor) as an electronic device, a solar cell, a chemical sensor, an OLED (Organic Light Emitting Diode) as an optical device, There is a photodetector. Devices using these organic substances are used by using a method that takes advantage of the properties unique to the organic substances.

  Thus, the organic semiconductor FET is expected as a promising device in the future. However, a method for evaluating the characteristics of the organic semiconductor FET has not yet been established. Therefore, in the past, macro electrical measurement methods used in inorganic semiconductor field effect transistors have also been used in organic semiconductor FETs.

  FIG. 10 shows a schematic explanatory diagram of a method for evaluating an inorganic semiconductor FET. As shown in FIG. 10, the inorganic semiconductor FET 90 has a source 91 and a drain 92, and a gate 93 is formed through an insulating film 94. When a voltage is applied to the gate 93, a channel layer 95 and a depletion layer 96 are formed. Further, when a potential difference is applied to the source 91 and the drain 92, a current flows. As an evaluation method in such a semiconductor FET 90, a capacitance-voltage (C-V) measurement 97 and a conductance-voltage (G-V) measurement 98 are used.

  In CV measurement, it is possible to see the movement of electric charges, so that the influence of fixed charges such as the formation of a depletion layer and impurities in an oxide film can be examined by measuring the capacitance between the gate and the source or drain. it can. In addition, since the GV measurement is a method of directly measuring the movement of the mobile charge itself, electrons flowing through the channel layer of the FET can be observed, and the channel formation between the source and drain can be measured.

In addition, as a method for evaluating the inorganic semiconductor FET, there is a method using a second harmonic (for example, Non-Patent Document 1). In this method, the second-order harmonic is used to evaluate the FET insulating layer, and it has been proposed as a technique for estimating the impurity density and trap density in the insulating layer. Further, attention is focused on an inorganic insulating layer, and a fixed charge generates a second harmonic in the insulator.
Z.Marka, SKSingh, SCLee, J.Kavich, B.Glebov, SNRashkeev, APKarmarkar, RGAlbridge, STPantelides, RDSchrimpf, DMFleetwood, and NHTolk, "Characterization of X-Ray Radiation Damage in Si / SiO2 Structures Using Second-Harmonic Generation" , IEEE TRANSACTIONS ON NUCLEAR SCIENCE, Vol.47, No.6, DECEMBER, 2256-2261 (2000)

  However, in an organic semiconductor FET (Field Effect Transistor), an evaluation method using CV measurement or GV measurement used for an inorganic semiconductor FET is not suitable. This is because the channel of the inorganic semiconductor FET is formed by charges supplied from the inside of the semiconductor, whereas the channel of the organic semiconductor FET is formed by using injected charges from the electrodes as a carrier supply source. In addition, since the nature of the organic semiconductor located between the source and the drain is not a semiconductor property but a dielectric property, whether or not conventional CV measurement or GV measurement is suitable. It is not clear.

  Even if the evaluation method used for inorganic semiconductor FETs is used for organic semiconductor FETs with different operating mechanisms, the correct physical properties of organic semiconductor FETs cannot be evaluated. Since improvement cannot be expected, a new evaluation method will be required. The present invention has been made to solve such problems, and an object thereof is to provide an effective method for evaluating an organic semiconductor FET and an evaluation apparatus using the method.

  The object of the present invention is to pay attention to dielectric polarization and electrical conduction, which are essential characteristics of organic semiconductors, and to improve the operating characteristics of organic semiconductor FETs, and to perform new measurements in place of conventional CV measurement and GV measurement. It is to propose a method, extract parameters necessary for device design using it, and feed back to the design. In particular, for organic semiconductors, since there is no ideal theoretical model that describes device operation, it is urgent to develop a new measurement method that replaces the conventional measurement method.

  In the organic semiconductor FET evaluation method according to the aspect of the present invention, a voltage is applied between the gate of the organic semiconductor FET and between the source and the drain, and the organic semiconductor FET is in a state in which the voltage is applied. High-order harmonic light emitted from the channel formation region where the light is incident on the channel formation region in the organic layer located between the drains and having the possibility of forming the channel layer. And measuring the conductance and / or electric field distribution in the channel formation region based on the intensity of the detected higher-order harmonic light. By using high-order harmonic light, it is possible to monitor channel formation, channel conductance, and channel layer electric field distribution in the organic semiconductor FET.

  An organic semiconductor FET evaluation apparatus according to another aspect of the present invention includes: a light source; a gate of the organic semiconductor FET; a power source that applies a voltage between a source and a drain; and a voltage that is applied by the power source. An organic semiconductor FET evaluation apparatus comprising: a detector that detects high-order harmonic light generated by irradiating the organic semiconductor FET with light from the light source.

  According to the characteristic measuring method and the evaluation apparatus according to the present invention, it is possible to monitor the channel formation, the channel conductance, and the electric field distribution of the channel layer in a non-contact manner by measuring the intensity change of the high-order harmonic light. . By observing the state of the channel layer, the present invention is an effective new method for evaluating an organic semiconductor FET, and it is possible to improve the device characteristics of the organic semiconductor FET by feeding back it.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In the present embodiment, the present invention is applied to an evaluation method and an evaluation apparatus for an organic semiconductor FET. The organic semiconductor FET evaluation method according to the present embodiment uses high-order harmonics generated by irradiating light to the polarization generated at the interface between the gate insulating layer and the channel layer of the organic semiconductor FET.

  Specifically, in the organic semiconductor FET, when the channel is formed or the conductance of the channel changes, the amount of polarization generated in the organic semiconductor layer changes, so that the intensity of the higher-order harmonic light changes. . By measuring the intensity of the higher-order harmonic light, the characteristics of the organic semiconductor FET can be evaluated. The reason why high-order harmonics are used is that there is no carrier generation by the direct excitation process from the valence band to the conduction band, so that the electric field distribution in the organic matter can be observed by the non-destructive process.

  The characteristics here are whether or not a channel layer is formed in the organic semiconductor FET and the electric field distribution in the channel layer. Even when the channel layer is formed, it is possible to determine whether the organic semiconductor FET is a sample having a good ON / OFF ratio by measuring the intensity change with respect to the gate voltage of high-order harmonic light. .

  Further, the second harmonic light (SHG: Second Harmonic Generation) may be used as the higher harmonic light. This is because SHG light is easier to measure because it is stronger than other high-order harmonics.

  Here, the organic semiconductor FET will be described. The organic semiconductor here is an organic substance having a possibility of constituting a channel of the FET, and is not necessarily a substance having properties of a conventional inorganic semiconductor. That is, it is an organic substance that is formed between the drain and the source and has a possibility of forming a channel layer by applying a voltage to the gate.

FIG. 1 shows an example of a schematic configuration diagram of the organic semiconductor FET 1. In the organic semiconductor FET 1, a source 13 and a drain 14 are formed on the SiO ₂ insulating layer 12. An organic semiconductor layer 15 is formed so as to cover the source 13 and the drain 14. An example of the organic semiconductor layer 15 is one of a low molecular weight molecule such as pentacene, phthalocyanine, and C60, a polymer such as polyparaphenylene vinylene, and polythiophene, or a combination thereof. A gate 11 is formed on the opposite side of the SiO ₂ insulating layer 12 from the source 13 and drain 14 sides. This structure is called a bottom contact type, but may be a top contact type (see FIG. 1B).

  FIG. 2 shows a schematic cross-sectional view of the schematic structure of the organic semiconductor FET 1 shown in FIG. As shown in FIG. 2, in the organic semiconductor FET 1, a voltage is applied to the gate electrode 11, and a voltage is applied to the gate electrode 11, whereby a channel layer 16 is formed between the source 13 and the drain 14. As a result, a current flows in the channel layer 16.

  The channel layer of the inorganic semiconductor FET is formed by carriers of the semiconductor layer between the drain and the source, whereas the channel layer of the organic semiconductor FET is formed by carriers injected from the drain and source electrodes. Has been. Thus, the expression mechanism is different between the channel layer of the inorganic semiconductor FET and the channel layer of the organic semiconductor FET. Therefore, in the evaluation method of the organic semiconductor FET according to the present embodiment, paying attention to the fact that the organic semiconductor layer 15 between the drain 14 and the source 13 is dielectric, the dielectric generated in the organic semiconductor layer 15 The intensity of high-order harmonic light that detects polarization is measured.

  In order to measure the intensity of high-order harmonic light, in the inspection method according to the embodiment, light is incident on the channel formation region 17 formed between the source 13 and the drain 14 (see FIG. 3). The channel formation region 17 is a region where a channel layer may be formed between the drain and the source when a voltage is applied to the gate. The incident light at this time must be light having a wavelength longer than the absorption edge of the organic semiconductor layer 15. Further, since the light emitted from the channel layer 16 is a combined wave of reflected light (fundamental light) and high-order harmonic light, it is necessary to separate it. High-order harmonic light is light having a frequency that is an integral multiple of reflected light (fundamental light). Therefore, by using a high-pass filter, higher-order harmonic light is separated from reflected light (fundamental light). Is extracted.

  FIG. 4 shows a structural diagram of the inspection apparatus according to the present embodiment. An IR pass filter 32 a is located in front of the laser 31 and transmits only the laser light from the laser 31. Thereafter, the laser beam transmitted from the laser 31 through the IR pass filter 32a is reflected by the mirror 33 and is incident on the polarizing plate 34a. As for the light incident on the polarizing plate 34a, only the light in the direction parallel to the angle of the polarizer is transmitted.

  The light that has passed through the polarizing plate 34a passes through the IR pass filter 32b. Here, light such as stray light can be cut. The light that has passed through the IR pass filter 32b is collected by the lens 35a and passes through a low-pass filter 36 that cuts light having a wavelength half that of the light emitted from the laser 31. The light that has passed through the low-pass filter 36 is incident on the sample 38.

  The light generated from the sample 38 passes through the IR cut filter 37. At this time, the basic light is cut off. The light transmitted through the IR cut filter 37 is diffused into parallel light by the lens 35b and passes through the polarizing plate 34b. Thereafter, the light is condensed by the lens 35 c and is incident on the monochromator 39. The light incident on the monochromator 39 is measured for each wavelength, and the light intensity is amplified by the photomultiplier 40 and measured.

  By doing so, only light in a certain wavelength region from light emitted from the laser 31 is incident on the sample 38, and only high-order harmonic light is extracted from the light emitted from the sample 38. Yes.

Here, as an example, three organic semiconductor FET samples (sample A, sample B, and sample C) are prepared and evaluated by the organic semiconductor FET evaluation method according to the present embodiment. In this case, second harmonic light (SHG light: Second Harmonic Generation) is used as high-order harmonic light. Sample A is an organic semiconductor FET capable of good operation, and has a small leakage current when no gate voltage is applied, and a drain-source current I _ds when no gate voltage is applied. This sample has a large ratio to the drain-source current I _ds when a gate voltage is applied. Sample B is a sample with a large leakage current when no gate voltage is applied. Sample C is a sample in which almost no current flows even when a gate voltage is applied. Sample B and Sample C are organic semiconductor FETs that are determined to have defects as organic semiconductor FETs.

The IV curve in each sample is shown in FIG. 5A is an IV curve of sample A, FIG. 5B is an IV curve of sample B, and FIG. 5C is an IV curve of sample C. In each graph, the vertical axis represents the drain-source current I _ds , and the horizontal axis represents the potential difference V _ds applied between the drain and the source.

As shown in FIG. 5 (a), sample A drain when the gate voltage is not applied - source current I _ds - drain when the source current I _ds is the gate voltage V _{g =} -70V applied Since the ratio of these two currents is large, the current value can be greatly different between the state in which the sample A is turned on and the state in which the sample A is turned off. This indicates that it is possible to perform a good operation.

In Sample B, as shown in FIG. 5B, when the gate voltage V _g = −70 V is applied even when the gate voltage is not applied, the drain-source current I _ds is large. Since the current ratio with the drain-source current I _ds is also small, it is determined as a defective organic semiconductor FET. In Sample C, as shown in FIG. 5C, the drain-source current I _ds is small in the state where the gate voltage is not applied, but the gate voltage V _g = −70 V is applied. Even in the state, since the drain-source current _Ids is small, the ratio of the two currents is small, so that the organic semiconductor FET is determined to be defective.

First, FIG. 6 shows the drain-source voltage and gate voltage dependence of the SHG light intensity of Sample A. The vertical axis represents the intensity of SHG light, and the horizontal axis represents time. At this time, in order to measure the SHG light, the measurement is performed by changing the drain-source voltage V _ds or the gate voltage V _g every 500 seconds. The incident light used for the generation of the SHG light is light having a wavelength λ = 1120 nm.

First, the SHG light intensity is measured for 500 seconds with the drain-source voltage V _ds = 0 V and the gate voltage V _g = 0 V (FIG. 6A). Next, the drain-source voltage V _ds is changed to −90 V, and the SHG light intensity is measured for 500 seconds (FIG. 6B). Next, the gate voltage V _g is changed to −90 V, and the SHG light intensity is measured for 500 seconds (FIG. 6C). Next, the gate voltage V _g is changed to 0 V, and the SHG light intensity is measured for 500 seconds (FIG. 6D). Finally, the drain-source voltage V _ds is changed to 0 V, and the SHG light intensity is measured for 500 seconds (FIG. 6E).

A first initial state, the drain - source voltage _V ds = 0V, the state of the gate voltage _V g = 0V, SHG light intensity is weak (see FIG. 6 (a)). Thereafter, the SHG light intensity is increased by applying the drain-source voltage _Vds (see FIG. 6B). This is presumably because dielectric polarization occurred in the organic semiconductor layer by applying a potential difference between the drain and the source.

Thereafter, a gate voltage _Vg is applied, whereby carriers flow into the organic semiconductor layer from the drain electrode and the source electrode to form a channel layer, and current flows in the channel layer (FIG. 6C). )reference). At this time, since the amount of dielectric polarization generated in the organic semiconductor layer is reduced, the SHG light intensity is significantly reduced.

When the gate voltage V _{g is set} to V _g = 0V, the channel layer disappears, and the dielectric polarization generated in the organic semiconductor layer is formed again (see FIG. 6D). At this time, the SHG light intensity significantly increases. Thereafter, when the drain-source voltage _{Vds is set} to _Vds = 0V, the polarization between the organic semiconductor layer and the insulating layer disappears, and the SHG light intensity is significantly reduced (see FIG. 6E). 6 (b) and 6 (d) have substantially the same SHG light intensity, and FIGS. 6 (a) and 6 (e) have substantially the same SHG light intensity, this result is reproducible. It is considered expensive.

  It is effective to evaluate the characteristics of the organic semiconductor FET by utilizing the fact that the intensity of the SHG light is changed by the movable charge generated by the change in conductance of the channel layer forming region in the organic semiconductor FET. It is shown that.

Next, the dependence of the SHG light intensity on the drain-source voltage and gate voltage in Sample B is shown in FIG. The measurement method is the same as that for sample A. The results in the initial state and the state in which the drain-source voltage V _ds is applied are the same as those of the sample A (see FIGS. 7A and 7B).

  However, as shown in FIG. 7C, the SHG light intensity does not decrease even when the gate voltage is applied. This is because in the organic semiconductor FET of Sample B, no current flows between the source and the drain, and it is considered that the gate voltage did not affect the formation of dielectric polarization. That is, it is considered that the channel layer is not formed in the sample B. From these facts, it is considered that in the sample B, the organic semiconductor FET cannot operate effectively.

Finally, the drain-source voltage and gate voltage dependence of the SHG light intensity in Sample C is shown in FIG. The measurement method is the same as that for sample A. The results in the initial state and the state in which the drain-source voltage V _ds is applied are the same as those of the sample A (see FIGS. 8A and 8B). Further, in FIG. 8C as well as the sample B, there is no decrease. That is, it is considered that the sample C is an organic semiconductor FET in which a channel layer is not formed and cannot operate effectively.

  From the above, by measuring the SHG light intensity, it can be determined whether or not the channel layer in the organic semiconductor is formed, and the operation of the organic semiconductor FET can be evaluated. In addition, since the generation and extinction of SHG light is linked with the ON / OFF of channel conductance, the ON / OFF state of the organic FET can be optically detected by detecting the SHG light.

Next, FIG. 9 shows the SHG light intensity when the drain-source voltage _Vds is constant and the gate voltage is changed. The vertical axis represents SHG light intensity, and the horizontal axis represents time. At this time, in order to generate SHG light, the drain-source voltage _Vds or the gate voltage _Vg is changed every 400 seconds. The incident light used for the generation of the SHG light is light having a wavelength λ = 1120 nm. Furthermore, the sample used at this time is the sample A used in the above experiment.

First, the SHG light intensity is measured for 400 seconds with the drain-source voltage V _ds = 0 V and the gate voltage V _g = 0 V (FIG. 9A). Next, the drain-source voltage V _ds is changed to −90 V, and the SHG light intensity is measured for 400 seconds (FIG. 9B). Next, the gate voltage V _g is changed to −30 V, and the SHG light intensity is measured for 400 seconds (FIG. 9C). Next, the gate voltage V _g is changed to −60 V, and the SHG light intensity is measured for 400 seconds (FIG. 9D). Next, the gate voltage V _g is changed to −90 V, and the SHG light intensity is measured for 400 seconds (FIG. 9E). Next, the gate voltage V _g is changed to 0 V, and the SHG light intensity is measured for 400 seconds (FIG. 9F). Finally, the drain-source voltage _Vds = 0V is changed, and the SHG light intensity is measured for 400 seconds (FIG. 9 (g)).

  From FIG. 9B to FIG. 9F, the drain-source voltage is kept constant at -90V, and the gate voltage is changed from 0V to -30V, -60V, and -90V. As shown in FIGS. 9B to 9E, it can be seen that the SHG light intensity decreases as the gate voltage increases. From these facts, it is considered that the SHG light intensity changes corresponding to the value of the current flowing between the drain and the source. Therefore, it is considered that the conductivity of the channel layer can be evaluated by measuring the SHG light intensity.

  From the above, it is possible to monitor channel formation and channel conductance by measuring a change in the intensity of high-order harmonic light. This makes it possible to evaluate the conduction of carriers in the organic semiconductor FET by measuring the intensity of high-order harmonic light. That is, the state of the channel layer can be observed, which can be a new method for evaluating the organic semiconductor FET.

  Furthermore, by using spectroscopic techniques such as higher harmonics, it is possible to change the measurement wavelength over a wide range, and if the energy involved in the measurement object is different, they can be observed separately. . Moreover, since it can be optically inspected, the organic semiconductor FET can be evaluated in a non-contact manner. Furthermore, since polarized wave input / output is possible, information on the electric field distribution in the organic matter can be obtained by appropriately controlling the polarization direction of the input / output wave. This makes it possible to measure the electric field distribution in the direction perpendicular to the source-drain connection direction as well as the source-drain connection direction in the organic substance. These also make it possible to measure conductance or electric field distribution having spatial anisotropy.

  Furthermore, when combined with a microscope, it is possible to measure a minute region, and to map a potential distribution in the horizontal direction between channels. Further, by using other lasers as attachments, it is considered possible to obtain not only the electric field but also information essential to device operation such as charge distribution. Further, in the method of the present invention, since there is no generation of optical carriers that occur when measuring an organic semiconductor FET by optical absorption measurement by applying an electric field, nondestructive measurement can be performed.

  From these, not only improvement of element characteristics by feeding back element parameters obtained by evaluation is desired, but it is also possible to evaluate the actually created elements in a non-contact manner. It is also possible to do.

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. Moreover, in this Embodiment, although the result of having produced | generated SHG light by infrared light was shown, this invention is not limited to this.

Schematic configuration of organic semiconductor FET Schematic cross-sectional view of the schematic configuration of the organic semiconductor FET shown in FIG. Schematic diagram of SHG light generated when light is incident on the organic semiconductor FET shown in FIG. Structure diagram of inspection apparatus according to Embodiment 1 IV curve for three samples Dependence of SHG light intensity on sample A on gate voltage and source-drain potential difference Dependence of SHG light intensity on sample B on gate voltage and source-drain potential difference Dependence of SHG light intensity on sample C on gate voltage and source-drain potential difference Change diagram of sample A when the gate voltage of SHG light intensity is changed Schematic explanatory diagram of a method for evaluating inorganic semiconductor FETs

Explanation of symbols

11 Gate 12 Insulating layer 13 Source 14 Drain 15 Organic semiconductor layer 16 Channel layer 17 Channel forming region 31 Laser 32 IR pass filter 33 Mirror 34 Polarizer 35 Lens 36 Low pass filter 37 IR cut filter 38 Sample 39 Monochromator 40 Photomultiplier 91 Source 92 Drain 93 Gate 94 Insulating layer 95 Channel layer 96 Depletion layer 97 CV measurement 98 GV measurement

Claims (9)

A voltage is applied between the gate of the organic semiconductor field effect transistor and between the source and drain,
In the organic semiconductor field effect transistor in a state where the voltage is applied, light is incident on a channel formation region in the organic material layer located between the source and the drain and in which a channel layer may be formed. And
Detecting high-order harmonic light emitted from the channel forming region where the light is incident;
Measuring conductance and / or electric field distribution in the channel formation region according to the intensity of the detected higher harmonic light;
Method for measuring characteristics of organic semiconductor field effect transistor.   The method for measuring characteristics of an organic semiconductor field effect transistor according to claim 1, wherein the high-order harmonic light is second-order harmonic light.   3. The organic according to claim 1, wherein the measurement of the conductance or electric field distribution includes a measurement of spatially anisotropic conductance and / or electric field distribution performed by polarizing the incident light. A method for measuring characteristics of a semiconductor field effect transistor.   The intensity of the high-order harmonic light when a voltage is applied between the drain and source, and the intensity of the high-order harmonic light when a voltage is applied between the drain and source and a voltage is also applied to the gate The method of measuring characteristics of an organic semiconductor field effect transistor according to any one of claims 1 to 3, wherein conductance and / or electric field distribution in the channel formation region is measured based on the above.   The intensity of the high-order harmonic light when a voltage is applied between the drain and source, and the intensity of the high-order harmonic light when a voltage is applied between the drain and source and a voltage is also applied to the gate The method for measuring characteristics of an organic semiconductor field effect transistor according to any one of claims 1 to 3, wherein whether or not the channel layer is formed on the organic material is measured based on the method.   6. The method of measuring characteristics of an organic semiconductor field effect transistor according to claim 1, wherein light incident on the channel formation region is laser light.   The organic substance located between the source and the drain is one of a low molecular weight molecule such as pentacene, phthalocyanine, and a polymer such as C60, a polymer such as polyparaphenylene vinylene, and polythiophene, or a combination thereof. The characteristic measuring method of the organic-semiconductor field effect transistor as described in any one of Claims 1 thru | or 6. A light source;
A power source for applying a voltage between the gate of the organic semiconductor field effect transistor and between the source and drain;
An organic semiconductor field effect transistor having a detector for detecting high-order harmonic light generated by irradiating light from the light source to the organic semiconductor field effect transistor in a state where a voltage is applied by the power source. Evaluation device.   The evaluation device for an organic semiconductor field effect transistor according to claim 8, wherein the light source is a laser.

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