Energy level consideration of source/channel/drain for performance enhancements of N- and P-channel organic FETs

T. Yokoyama, T. Nishimura, K. Kita, Kentaro Kyuno, A. Toriumi

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Both n and p-channel operation of pentacene TFTs have been recently reported from the viewpoints of the channel substrate [1] and the appropriate source(S)/drain(D) material selection [2]. This paper discusses a possible way to achieve better FET performances for both channels as well as a determination mechanism of the channel type. We investigated perfluoropentace (C 22F14) (PF-pentacene) for n-channel and pentacene (C 22H14) for p-channel FETs. On the basis of the energy level consideration for both channel material and S/D metals, we show a systematic guideline for achieving a better OFET performance. First, the crystalline structures of PF-pentacene and pentacene are shown in Fig. 1. Although the XRD pattern of two materials is similar to each other, there is a big difference of the SEM picture. This fact may be related to the effective mobility in the channel due to a difference of the grain-grain interaction between two materials. But, this paper focuses another aspect determining the OFET performance. The energy level structures of PF-pentacene and pentacene were determined by using the photoemission apparatus, AC-3 (Rikenkeiki), and the spectroscopic ellipsometry (SE). 50nm thick PF-pentacene and pentacene films were grown by the vacuum evaporation on 30 nm-thick SiO2 thermally grown on p- and n-silicon substrates, respectively. From the AC-3 results, HOMO levels of PF-pentacene and pentacene were estimated to be 6.7eV and S.0eV, as shown in Fig.2. On the other hand, LUMO-HOMO energy gaps of them were estimated to be 1.7eV and 1.8eV from the absorption edge of SE as shown in Fig. 3. Thus, LUMO levels were calculated to be S.0eV for PF-pentacene and 3.2eV for pentacene, respectively. The energy level diagrams of them are depicted in Fig. 4, together with the work-function (WF) levels of Au and Al. It is noted that the energy barrier is very small between the LUMO level of PF-pentacene and the WF of Au, while the HOMO level of pentacene is quite similar to the WF of Au. Those results guide us how to achieve higher FET performance in terms of both substrate material and S/D material selections. Fig. 5 shows Ids-Yds characteristics for both n- and p-channel FETs by changing the substrate and S/D materials. FET size was W/L=1000μm/300μm and the measurement was conducted in a vacuum. The mobility of pentacene and PF-pentacene FET with Au source drain electrode was 0.2 cm2/Vs and 0.02 cm2/Vs, respectively. Note that Al(S)/PF-pentacene/Au(D) structure is better than Au(S)/PF-pentacene/Au(D) for n-channel FET, while Au/pentacene/Au one is better than any Al electrode FETs for p-channel one. Since Al source for PF-pentacene and Au source for pentacene have no carrier injection barrier (a very small if any) expected from the results in Fig. 4, while Al drain for PF-pentacene and Al source for pentacene lead to high barriers. Yasuda et al. reported an n-channel pentacene FET operation with calcium S/D electrodes on the basis of the energy level consideration [2]. However, electron mobility in pentacene was much smaller than our PF-pentacene FET mobility. Thus, it can be concluded that appropriate combination of the channel materials with S and D metals will be a key to achieve higher performance dual channel FETs. Furthermore, it is interesting to note that a finite offset of Vds in Fig. 5 enables to realize a switched diode, which means a diode on-state and no current off-state, in addition to the simple FET characteristics. This function may lead to a new circuit operation mode of OFETs without any dopant control employed in the conventional semiconductor technology. Finally, it is worthy of mention that it will be interesting to apply these structures to the bilayer ambipolar devices. The bilayer FET of pentacene/PF-pentacene/SoO2/Si structure with Au S/D electrodes clearly shows ambipolar Ids-Vds characteristics as shown in Fig. 6. In case of bilayer device with different S/D electrodes, it is expected to show novel functional characteristics. In conclusion, we investigated the channel material selection associated with the S/D electrodes on the basis of the energy level alignment of the source/channel/drain structure. We also discussed a switched diode using a simple OFET in terms of a functional device. These results are useful for designing high performance organic device family.

Original languageEnglish
Title of host publicationDevice Research Conference - Conference Digest, DRC
Pages107-108
Number of pages2
Volume2005
DOIs
Publication statusPublished - 2005
Externally publishedYes
Event63rd Device Research Conference, DRC'05 - Santa Clara, CA
Duration: 2005 Jun 202005 Jun 22

Other

Other63rd Device Research Conference, DRC'05
CitySanta Clara, CA
Period05/6/2005/6/22

Fingerprint

Field effect transistors
Electron energy levels
Organic field effect transistors
Electrodes
Diodes
Spectroscopic ellipsometry
Substrates
Vacuum evaporation
Electron mobility
Energy barriers
Photoemission
Metals
Calcium
Energy gap
Doping (additives)
Vacuum
Semiconductor materials
Crystalline materials

ASJC Scopus subject areas

  • Engineering(all)

Cite this

Yokoyama, T., Nishimura, T., Kita, K., Kyuno, K., & Toriumi, A. (2005). Energy level consideration of source/channel/drain for performance enhancements of N- and P-channel organic FETs. In Device Research Conference - Conference Digest, DRC (Vol. 2005, pp. 107-108). [1553078] https://doi.org/10.1109/DRC.2005.1553078

Energy level consideration of source/channel/drain for performance enhancements of N- and P-channel organic FETs. / Yokoyama, T.; Nishimura, T.; Kita, K.; Kyuno, Kentaro; Toriumi, A.

Device Research Conference - Conference Digest, DRC. Vol. 2005 2005. p. 107-108 1553078.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Yokoyama, T, Nishimura, T, Kita, K, Kyuno, K & Toriumi, A 2005, Energy level consideration of source/channel/drain for performance enhancements of N- and P-channel organic FETs. in Device Research Conference - Conference Digest, DRC. vol. 2005, 1553078, pp. 107-108, 63rd Device Research Conference, DRC'05, Santa Clara, CA, 05/6/20. https://doi.org/10.1109/DRC.2005.1553078
Yokoyama T, Nishimura T, Kita K, Kyuno K, Toriumi A. Energy level consideration of source/channel/drain for performance enhancements of N- and P-channel organic FETs. In Device Research Conference - Conference Digest, DRC. Vol. 2005. 2005. p. 107-108. 1553078 https://doi.org/10.1109/DRC.2005.1553078
Yokoyama, T. ; Nishimura, T. ; Kita, K. ; Kyuno, Kentaro ; Toriumi, A. / Energy level consideration of source/channel/drain for performance enhancements of N- and P-channel organic FETs. Device Research Conference - Conference Digest, DRC. Vol. 2005 2005. pp. 107-108
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abstract = "Both n and p-channel operation of pentacene TFTs have been recently reported from the viewpoints of the channel substrate [1] and the appropriate source(S)/drain(D) material selection [2]. This paper discusses a possible way to achieve better FET performances for both channels as well as a determination mechanism of the channel type. We investigated perfluoropentace (C 22F14) (PF-pentacene) for n-channel and pentacene (C 22H14) for p-channel FETs. On the basis of the energy level consideration for both channel material and S/D metals, we show a systematic guideline for achieving a better OFET performance. First, the crystalline structures of PF-pentacene and pentacene are shown in Fig. 1. Although the XRD pattern of two materials is similar to each other, there is a big difference of the SEM picture. This fact may be related to the effective mobility in the channel due to a difference of the grain-grain interaction between two materials. But, this paper focuses another aspect determining the OFET performance. The energy level structures of PF-pentacene and pentacene were determined by using the photoemission apparatus, AC-3 (Rikenkeiki), and the spectroscopic ellipsometry (SE). 50nm thick PF-pentacene and pentacene films were grown by the vacuum evaporation on 30 nm-thick SiO2 thermally grown on p- and n-silicon substrates, respectively. From the AC-3 results, HOMO levels of PF-pentacene and pentacene were estimated to be 6.7eV and S.0eV, as shown in Fig.2. On the other hand, LUMO-HOMO energy gaps of them were estimated to be 1.7eV and 1.8eV from the absorption edge of SE as shown in Fig. 3. Thus, LUMO levels were calculated to be S.0eV for PF-pentacene and 3.2eV for pentacene, respectively. The energy level diagrams of them are depicted in Fig. 4, together with the work-function (WF) levels of Au and Al. It is noted that the energy barrier is very small between the LUMO level of PF-pentacene and the WF of Au, while the HOMO level of pentacene is quite similar to the WF of Au. Those results guide us how to achieve higher FET performance in terms of both substrate material and S/D material selections. Fig. 5 shows Ids-Yds characteristics for both n- and p-channel FETs by changing the substrate and S/D materials. FET size was W/L=1000μm/300μm and the measurement was conducted in a vacuum. The mobility of pentacene and PF-pentacene FET with Au source drain electrode was 0.2 cm2/Vs and 0.02 cm2/Vs, respectively. Note that Al(S)/PF-pentacene/Au(D) structure is better than Au(S)/PF-pentacene/Au(D) for n-channel FET, while Au/pentacene/Au one is better than any Al electrode FETs for p-channel one. Since Al source for PF-pentacene and Au source for pentacene have no carrier injection barrier (a very small if any) expected from the results in Fig. 4, while Al drain for PF-pentacene and Al source for pentacene lead to high barriers. Yasuda et al. reported an n-channel pentacene FET operation with calcium S/D electrodes on the basis of the energy level consideration [2]. However, electron mobility in pentacene was much smaller than our PF-pentacene FET mobility. Thus, it can be concluded that appropriate combination of the channel materials with S and D metals will be a key to achieve higher performance dual channel FETs. Furthermore, it is interesting to note that a finite offset of Vds in Fig. 5 enables to realize a switched diode, which means a diode on-state and no current off-state, in addition to the simple FET characteristics. This function may lead to a new circuit operation mode of OFETs without any dopant control employed in the conventional semiconductor technology. Finally, it is worthy of mention that it will be interesting to apply these structures to the bilayer ambipolar devices. The bilayer FET of pentacene/PF-pentacene/SoO2/Si structure with Au S/D electrodes clearly shows ambipolar Ids-Vds characteristics as shown in Fig. 6. In case of bilayer device with different S/D electrodes, it is expected to show novel functional characteristics. In conclusion, we investigated the channel material selection associated with the S/D electrodes on the basis of the energy level alignment of the source/channel/drain structure. We also discussed a switched diode using a simple OFET in terms of a functional device. These results are useful for designing high performance organic device family.",
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N2 - Both n and p-channel operation of pentacene TFTs have been recently reported from the viewpoints of the channel substrate [1] and the appropriate source(S)/drain(D) material selection [2]. This paper discusses a possible way to achieve better FET performances for both channels as well as a determination mechanism of the channel type. We investigated perfluoropentace (C 22F14) (PF-pentacene) for n-channel and pentacene (C 22H14) for p-channel FETs. On the basis of the energy level consideration for both channel material and S/D metals, we show a systematic guideline for achieving a better OFET performance. First, the crystalline structures of PF-pentacene and pentacene are shown in Fig. 1. Although the XRD pattern of two materials is similar to each other, there is a big difference of the SEM picture. This fact may be related to the effective mobility in the channel due to a difference of the grain-grain interaction between two materials. But, this paper focuses another aspect determining the OFET performance. The energy level structures of PF-pentacene and pentacene were determined by using the photoemission apparatus, AC-3 (Rikenkeiki), and the spectroscopic ellipsometry (SE). 50nm thick PF-pentacene and pentacene films were grown by the vacuum evaporation on 30 nm-thick SiO2 thermally grown on p- and n-silicon substrates, respectively. From the AC-3 results, HOMO levels of PF-pentacene and pentacene were estimated to be 6.7eV and S.0eV, as shown in Fig.2. On the other hand, LUMO-HOMO energy gaps of them were estimated to be 1.7eV and 1.8eV from the absorption edge of SE as shown in Fig. 3. Thus, LUMO levels were calculated to be S.0eV for PF-pentacene and 3.2eV for pentacene, respectively. The energy level diagrams of them are depicted in Fig. 4, together with the work-function (WF) levels of Au and Al. It is noted that the energy barrier is very small between the LUMO level of PF-pentacene and the WF of Au, while the HOMO level of pentacene is quite similar to the WF of Au. Those results guide us how to achieve higher FET performance in terms of both substrate material and S/D material selections. Fig. 5 shows Ids-Yds characteristics for both n- and p-channel FETs by changing the substrate and S/D materials. FET size was W/L=1000μm/300μm and the measurement was conducted in a vacuum. The mobility of pentacene and PF-pentacene FET with Au source drain electrode was 0.2 cm2/Vs and 0.02 cm2/Vs, respectively. Note that Al(S)/PF-pentacene/Au(D) structure is better than Au(S)/PF-pentacene/Au(D) for n-channel FET, while Au/pentacene/Au one is better than any Al electrode FETs for p-channel one. Since Al source for PF-pentacene and Au source for pentacene have no carrier injection barrier (a very small if any) expected from the results in Fig. 4, while Al drain for PF-pentacene and Al source for pentacene lead to high barriers. Yasuda et al. reported an n-channel pentacene FET operation with calcium S/D electrodes on the basis of the energy level consideration [2]. However, electron mobility in pentacene was much smaller than our PF-pentacene FET mobility. Thus, it can be concluded that appropriate combination of the channel materials with S and D metals will be a key to achieve higher performance dual channel FETs. Furthermore, it is interesting to note that a finite offset of Vds in Fig. 5 enables to realize a switched diode, which means a diode on-state and no current off-state, in addition to the simple FET characteristics. This function may lead to a new circuit operation mode of OFETs without any dopant control employed in the conventional semiconductor technology. Finally, it is worthy of mention that it will be interesting to apply these structures to the bilayer ambipolar devices. The bilayer FET of pentacene/PF-pentacene/SoO2/Si structure with Au S/D electrodes clearly shows ambipolar Ids-Vds characteristics as shown in Fig. 6. In case of bilayer device with different S/D electrodes, it is expected to show novel functional characteristics. In conclusion, we investigated the channel material selection associated with the S/D electrodes on the basis of the energy level alignment of the source/channel/drain structure. We also discussed a switched diode using a simple OFET in terms of a functional device. These results are useful for designing high performance organic device family.

AB - Both n and p-channel operation of pentacene TFTs have been recently reported from the viewpoints of the channel substrate [1] and the appropriate source(S)/drain(D) material selection [2]. This paper discusses a possible way to achieve better FET performances for both channels as well as a determination mechanism of the channel type. We investigated perfluoropentace (C 22F14) (PF-pentacene) for n-channel and pentacene (C 22H14) for p-channel FETs. On the basis of the energy level consideration for both channel material and S/D metals, we show a systematic guideline for achieving a better OFET performance. First, the crystalline structures of PF-pentacene and pentacene are shown in Fig. 1. Although the XRD pattern of two materials is similar to each other, there is a big difference of the SEM picture. This fact may be related to the effective mobility in the channel due to a difference of the grain-grain interaction between two materials. But, this paper focuses another aspect determining the OFET performance. The energy level structures of PF-pentacene and pentacene were determined by using the photoemission apparatus, AC-3 (Rikenkeiki), and the spectroscopic ellipsometry (SE). 50nm thick PF-pentacene and pentacene films were grown by the vacuum evaporation on 30 nm-thick SiO2 thermally grown on p- and n-silicon substrates, respectively. From the AC-3 results, HOMO levels of PF-pentacene and pentacene were estimated to be 6.7eV and S.0eV, as shown in Fig.2. On the other hand, LUMO-HOMO energy gaps of them were estimated to be 1.7eV and 1.8eV from the absorption edge of SE as shown in Fig. 3. Thus, LUMO levels were calculated to be S.0eV for PF-pentacene and 3.2eV for pentacene, respectively. The energy level diagrams of them are depicted in Fig. 4, together with the work-function (WF) levels of Au and Al. It is noted that the energy barrier is very small between the LUMO level of PF-pentacene and the WF of Au, while the HOMO level of pentacene is quite similar to the WF of Au. Those results guide us how to achieve higher FET performance in terms of both substrate material and S/D material selections. Fig. 5 shows Ids-Yds characteristics for both n- and p-channel FETs by changing the substrate and S/D materials. FET size was W/L=1000μm/300μm and the measurement was conducted in a vacuum. The mobility of pentacene and PF-pentacene FET with Au source drain electrode was 0.2 cm2/Vs and 0.02 cm2/Vs, respectively. Note that Al(S)/PF-pentacene/Au(D) structure is better than Au(S)/PF-pentacene/Au(D) for n-channel FET, while Au/pentacene/Au one is better than any Al electrode FETs for p-channel one. Since Al source for PF-pentacene and Au source for pentacene have no carrier injection barrier (a very small if any) expected from the results in Fig. 4, while Al drain for PF-pentacene and Al source for pentacene lead to high barriers. Yasuda et al. reported an n-channel pentacene FET operation with calcium S/D electrodes on the basis of the energy level consideration [2]. However, electron mobility in pentacene was much smaller than our PF-pentacene FET mobility. Thus, it can be concluded that appropriate combination of the channel materials with S and D metals will be a key to achieve higher performance dual channel FETs. Furthermore, it is interesting to note that a finite offset of Vds in Fig. 5 enables to realize a switched diode, which means a diode on-state and no current off-state, in addition to the simple FET characteristics. This function may lead to a new circuit operation mode of OFETs without any dopant control employed in the conventional semiconductor technology. Finally, it is worthy of mention that it will be interesting to apply these structures to the bilayer ambipolar devices. The bilayer FET of pentacene/PF-pentacene/SoO2/Si structure with Au S/D electrodes clearly shows ambipolar Ids-Vds characteristics as shown in Fig. 6. In case of bilayer device with different S/D electrodes, it is expected to show novel functional characteristics. In conclusion, we investigated the channel material selection associated with the S/D electrodes on the basis of the energy level alignment of the source/channel/drain structure. We also discussed a switched diode using a simple OFET in terms of a functional device. These results are useful for designing high performance organic device family.

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