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| 3. |
- Koo, S. M., et al.
(author)
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Ferroelectric Pb(Zr,Ti)O-3/Al2O3/4H-SiC diode structures
- 2002
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:5, s. 895-897
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Journal article (peer-reviewed)abstract
- Pb(Zr,Ti)O-3 (PZT) films (450 nm thick) were grown on 4H-silicon carbide (SiC) substrates by a pulsed-laser deposition technique. X-ray diffraction confirms single PZT phase without a preferred orientation. Stable capacitance-voltage (C-V) loops with low conductance (<0.1 mS/cm(2), tan deltasimilar to0.0007 at 400 kHz) and memory window as wide as 10 V were obtained when 5-nm-thick Al2O3 was used as a high band gap (E(g)similar to9 eV) barrier buffer layer between PZT (E(g)similar to3.5 eV) and SiC (E(g)similar to3.2 eV). High-frequency (400 kHz) C-V characteristics revealed clear accumulation, and depletion behavior. Although the charge injection from SiC is the dominant mechanism for C-V hysteresis in PZT/Al2O3/SiC, negligible sweep rate dependence and negligible applied bias dependence were observed compared to that of PZT/SiC. By using room-temperature photoilluminated C-V measurements, the interface states as well as the charge trapping in the PZT/Al2O3 stacks have been calculated.
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| 4. |
- Koo, S. M., et al.
(author)
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Ferroelectric Pb(Zr0.52Ti0.48)/SiC field-effect transistor
- 2003
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 83:19, s. 3975-3977
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Journal article (peer-reviewed)abstract
- Nonvolatile operation of ferroelectric gate field-effect transistors in silicon carbide (SiC) is demonstrated. Depletion mode transistors have been realized by forming a Pb(Zr0.52Ti0.48)O-3/Al2O3 gate stack on n-type epitaxial channel layer and p-type substrate of 4H-SiC. A memory window, as wide as 5 V, has been observed in the drain current and the ferroelectric gate voltage transfer characteristics. The transistor showed memory effect from room temperature up to 200 degreesC, whereas stable transistor operation was observed up to 300 degreesC. The retention of remnant polarization was preserved after 2x10(4) s at 150 degreesC with no bias on the gate.
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| 6. |
- Koo, S. M., et al.
(author)
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Processing and properties of ferroelectric Pb(Zr,Ti)O-3/silicon carbide field-effect transistor
- 2003
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In: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 57, s. 1221-1231
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Journal article (peer-reviewed)abstract
- Metal-ferroelectric-(insulator)-semiconductor MF(I)S structures have been fabricated and the properties of pulsed laser-deposited PZT/Al-2 O-3 gate stacks have been studied on n - and p -type 4H-SiC. Among several polytypes of SiC, 4H-SiC is considered as the most attractive one because of its wider bandgap (E-g congruent to 3.2 eV) as well as higher and more isotropic bulk mobility than other polytypes. Single PZT phase without a preferred orientation was confirmed by x-ray diffraction. The interface trap densities N-IT , fixed oxide charges Q(F) , and trapped oxide charges Q HY have been estimated by C-V curves with and without photo-illuminated measurements at room temperature. It is found that the charge injection from SiC is the dominant mechanism for C-V hysteresis. Importantly, with PZT/Al-2 O-3 gate stacks, superior C-V characteristics with negligible sweep rate dependence and negligible time dependence under the applied bias were obtained compared to PZT directly deposited on SiC. The MFIS structures exhibited very stable capacitance-voltage C-V loops with low conductance (<0.1 mS/cm(2) , tan delta similar to 0.0007 at 400 kHz) and memory window as wide as 10 V, when 5 nm-thick Al2O3 was used as a high bandgap (E-g similar to 9 eV) barrier buffer layer between PZT (E-g similar to 3.5 eV) and SiC (E-g similar to 3.2 eV). The structures have shown excellent electrical properties promising for the gate stacks as the SiC field-effect transistors (FETs). Depletion mode transistors were prepared by forming a Pb(Zr-0.52 Ti-0.48 )O-3 /Al-2 O-3 gate stack on 4H-SiC. Based on this structure, ferroelectric Pb(Zr,Ti)O-3 (PZT) thin films have been integrated on 4H-silicon carbide (SiC) in a SiC field-effect transistor process. Nonvolatile operation of ferroelectric-gate field-effect transistors in silicon carbide (SiC) is demonstrated.
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| 7. |
- Koo, S. -M, et al.
(author)
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Towards ferroelectric field effect transistors in 4H-silicon carbide
- 2002
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In: Materials Research Society Symposium - Proceedings. - Boston, MA. ; , s. 371-379
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Conference paper (peer-reviewed)abstract
- We report on the integration of ferroelectric Pb(Zr,Ti)O3 (PZT) thin films on 4H-silicon carbide and their electrical properties. The structures of metal-ferroelectric-(insulator)-semiconductor MF(I)S and metal-ferroelectric-metal-insulator-semiconductor MFMIS have been fabricated and characterized. The MFMIS structures of Au/PZT/Pt/Ti/SiO2/SiC have shown fully saturated P-E hysteresis loops with remnant polarization Pr = 14.2 ΌC/cm2 and coercive field Ec = 58.9 kV/cm. The MFIS structures exhibited stable capacitance-voltage C-V loops with low conductance (<0.1 mS/cm2, tan Ύ ∌ 0.0007 at 12 V, 400 kHz) and memory window as wide as 10 V, when a 5 nm-thick Al2O3 was used as a high bandgap (Eg ∌ 9 eV) barrier buffer layer between PZT (Eg ∌ 3.5 eV) and SiC (Eg ∌ 3.2 eV). Both structures on n- and p- SiC have shown electrical properties promising for the application to the gate stacks for the SiC field-effect transistors (FETs) and the design and process issues on different types of the metal-ferroelectric-silicon carbide field-effect transistors (FETs) have also been proposed.
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| 8. |
- Östling, Mikael, et al.
(author)
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Ferroelectric thin films on silicon carbide for next-generation nonvolatile memory and sensor devices
- 2004
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 469-70, s. 444-449
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Journal article (peer-reviewed)abstract
- Silicon carbide semiconductor technology has emerged as a very good candidate to replace traditional Si devices in special applications such as low loss power switching and high temperature electronics. Ferroelectric thin films exhibit interesting properties for use in semiconductor technology due to the spontaneous polarization which can be switched by an externally applied electric field, and thus are attractive for nonvolatile memory and sensor applications. In this work, the successful realization of ferroelectric thin films in SiC devices is described. The first experimental prototype devices are presented and discussed: A novel integration technique of junction metal-oxide-semiconductor field effect transistors (JMOSFETs) and nonvolatile FETs (NVFETs) on a single 4H-SiC substrate is presented. A constant current control device is based on the SiC JMOSFET. The drain current is effectively controlled and kept constant by a buried junction gate. A new high temperature SiC NVFET with a similar temperature stable current drive is also demonstrated. The nonvolatile memory device, based on the ferroelectric gate stack, was shown to operate up to 300 C with memory effect retained up to 200degreesC.
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| 9. |
- Cho, H., et al.
(author)
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Ultradeep, low-damage dry etching of SiC
- 2000
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:6, s. 739-741
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Journal article (peer-reviewed)abstract
- The Schottky barrier height (Phi(B)) and reverse breakdown voltage (V-B) of Au/n-SiC diodes were used to examine the effect of inductively coupled plasma SF6/O-2 discharges on the near-surface electrical properties of SiC. For low ion energies (less than or equal to 60 eV) in the discharge, there is minimal change in Phi(B) and V-B, but both parameters degrade at higher energies. Highly anisotropic features typical of through-wafer via holes were formed in SiC using an Al mask.
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| 10. |
- Danielsson, E, et al.
(author)
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Investigation of thermal properties in fabricated 4H-SiC high-power bipolar transistors
- 2002
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In: Materials Science Forum, Vols. 389-393. ; , s. 1337-1340
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Conference paper (peer-reviewed)abstract
- Silicon Carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of up to 600 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 degreesC, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. Physical device simulations have been used to analyze the measured data. The thermal conductivity is fitted to model the measured self-heating, and the lifetime in the base is fitted against the measurement of the current gain.
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