Towards Ferroelectric Field Effect Transistors in 4H-Silicon Carbide
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Towards Ferroelectric Field Effect Transistors in 4H-Silicon Carbide S.-M. Koo, S. I. Khartsev, C.-M. Zetterling, A. M. Grishin, and M. Östling Department of Microelectronics and Information Technology, KTH, Royal Institute of Technology, S-164 40 Stockholm-Kista, SWEDEN 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 =14.2µC/cm2 and coercive field Ec= 58.9 kV/cm. The MFIS structures exhibited stable capacitance-voltage C-V loops with low conductance (80oC) for 5 min and then in H2O:CH3CH(OH)CH3:HF (100:3:1) for 100 s. Prior to the ferroelectric material deposition, a sacrificial oxidation was performed at 1150oC in dry O2 for 60 min, and this sacrificial oxide was removed by etching in HF:H2O (1:1) for 10 min.
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Fig. 2 shows the typical pulsed laser deposition (PLD) system employed in our work. PLD is simple but very versatile technique in growing multi-component oxide thin films. A KrF excimer laser (248 nm wavelength) was used to ablate ceramic targets of PbZr0.52Ti0.48O3 and Al2O3 with 3.5 J/cm2 energy density per pulse. Al2O3 (5 nm) was deposited at a substrate temperature of 650oC and an oxygen pressure of 10 mTorr, and then PZT (~450 nm) was grown at 580-800 oC and 250 mTorr in oxygen, without breaking the atmosphere. All samples were post-annealed at 500 Torr in oxygen for 10 min and cooled down to room temperature at a rate of 15oC/min. After the laser deposition, a 200 nm-thick Au film was thermally evaporated through a shadow mask to form circular gate contacts with a diameter of 485 µm, and rf-magnetron sputtered Ni (500 nm) was used as a backside contact. Pump Oxygen Substrate Port Heater
Vacuum Chamber
Substrate Target
Plume
Focusing Lens Pulsed Excimer Laser
Target Port
Laser Port
Laser Window
Figure 2. Schematic configuration of the pulsed laser deposition (PLD) system
The crystalline quality of the layers was examined by x-ray diffraction (XRD) using a Siemens D5000 diffractometer. Ferroelectric hysteresis properties were measured by a commercial pulsed testing apparatus, Radiant Technologies RT66A. High frequency capacitance-voltage (C-V) characteristics were measured using a HP 4284A multi-frequency LCR meter. The schematic cross section of the fabricated MFMIS and MFIS structures are shown in Fig. 3 (a) and (b), respectively. Au Au
PZT
PZT
Pt 4H-SiC
SiO2
SiO2 or Al2O3
4H-SiC
Figure 3. Cross section of the fabricated MFMIS and MFIS structures
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RESULTS AND DISCUSSION
Pt (111)
The XRD patterns of the PZT films on SiC are shown in Fig. 4. The MFMIS structure of PZT on Pt/SiO2/SiC exhibits orientation of [100] and [101] reflections of PZT phase (see figure 2(a)). It was reported by
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