• ETRI Journal
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• 제30권6호
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• pp.826-832
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• 2008

The metal-ferroelectric-metal (MFM) capacitor in the ferroelectric random access memory (FeRAM) embedded RFID chip is used in both the memory cell region and the peripheral analog and digital circuit area for capacitance parameter control. The capacitance value of the MFM capacitor is about 30 times larger than that of conventional capacitors, such as the poly-insulator-poly (PIP) capacitor and the metal-insulator-metal (MIM) capacitor. An MFM capacitor directly stacked over the analog and memory circuit region can share the layout area with the circuit region; thus, the chip size can be reduced by about 60%. The energy transformation efficiency using the MFM scheme is higher than that of the PIP scheme in RFID chips. The radio frequency operational signal properties using circuits with MFM capacitors are almost the same as or better than with PIP, MIM, and MOS capacitors. For the default value specification requirement, the default set cell is designed with an additional dummy cell.

• The Korean Journal of Ceramics
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• 제6권2호
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• pp.138-142
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• 2000

Thin film $LiNbO_3$MFS (metal-ferroelectric-semiconductor) capacitor showed improved characteristics such as low interface trap density, low interaction with Si substrate, and large remanent polarization. This paper reports ferroelectric $LiNbO_3$thin films grown directly on p-type Si (100) substrates by 13.56 MHz RF magnetron sputtering system for FRAM (ferroelectric random access memory) applications. RTA (rapid thermal anneal) treatment was performed for as-deposited films in an oxygen atmosphere at $600^{\circ}C$ for 60sec. We learned from X-ray diffraction that the RTA treated films were changed from amorphous to poly-crystalline $LiNbO_3$which exhibited (012), (015), (022), and (023) plane. Low temperature film growth and post RTA treatments improved the leakage current of $LiNbO_3$films while keeping other properties almost as same as high substrate temperature grown samples. The leakage current density of $LiNbO_3$films decreased from $10^{-5}$ to $10^{-7}$A/$\textrm{cm}^2$ after RTA treatment. Breakdown electric field of the films exhibited higher than 500 kV/cm. C-V curves showed the clockwise hysteresis which represents ferroelectric switching characteristics. Calculated dielectric constant of thin film $LiNbO_3$illustrated as high as 27.9. From ferroelectric measurement, the remanent polarization and coercive field were achieved as 1.37 $\muC/\textrm{cm}^2$ and 170 kV/cm, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 추계학술대회 논문집 Vol.19
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• pp.135-136
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• 2006

Bismuth titanate ($Bi_4Ti_3O_{12}$, BIT) thin film has been studied intensively in the past decade due to its large remanent polarization, low crystallization temperature, and high Curie temperature. Substitution of various trivalent rare-earth cations (such as $La^{3+}$, $Nd^{3+}$, $Sm^{3+}$ and $Pr^{3+}$) in the BIT structure is known to improve its ferroelectric properties, such as remanent polarization and fatigue characteristics. Among them, neodymuim-substituted bismuth titanate, ((Bi, Nd)$_4Ti_3O_{12}$, BNT) has been receiving much attention due to its larger ferroelectricity. In this study, Ferroelectric $Bi_{3.3}Nd_{0.7}Ti_3O_{12}$ thin films were successfully fabricated by liquid delivery MOCVD process onto Pt(111)/Ti/$SiO_2$/Si(l00) substrates. Fabricated polycrystailine BNT thin films were found to be random orientations, which were confirmed by X-ray diffraction and scanning electron microscope analyses. The remanent polarization of these films increased with increase in annealing temperature. And the film also demonstrated fatigue-free behavior up to $10^{11}$ read/write switching cycles. These results indicate that the randomly oriented BNT thin film is a promising candidate among ferroelectric materials useful for lead-free nonvolatile ferroelectric random access memory applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.410-410
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• 2013

Next-generation nonvolatile memory (NVM) has attracted increasing attention about emerging NVMs such as ferroelectric random access memory, phase-change random access memory, magnetic random access memory and resistance random access memory (RRAM). Previous studies have demonstrated that RRAM is promising because of its excellent properties, including simple structure, high speed and high density integration. Many research groups have reported a lot of metal oxides as resistive materials like TiO2, NiO, SrTiO3 and ZnO [1]. Among them, the ZnO-based film is one of the most promising materials for RRAM because of its good switching characteristics, reliability and high transparency [2]. However, in many studies about ZnO-based RRAMs, there was a problem to get lower current level for reducing the operating power dissipation and improving the device reliability such an endurance and an retention time of memory devices. Thus in this paper, we investigated that highly reproducible bipolar resistive switching characteristics of W doped ZnO RRAM device and it showed low resistive switching current level and large ON/OFF ratio. This may be caused by the interdiffusion of the W atoms in the ZnO film, whch serves as dopants, and leakage current would rise resulting in the lowering of current level [3]. In this work, a ZnO film and W doped ZnO film were fabricated on a Si substrate using RF magnetron sputtering from ZnO and W targets at room temperature with Ar gas ambient, and compared their current levels. Compared with the conventional ZnO-based RRAM, the W doped ZnO ReRAM device shows the reduction of reset current from ~$10^{-6}$ A to ~$10^{-9}$ A and large ON/OFF ratio of ~$10^3$ along with self-rectifying characteristic as shown in Fig. 1. In addition, we observed good endurance of $10^3$ times and retention time of $10^4$ s in the W doped ZnO ReRAM device. With this advantageous characteristics, W doped ZnO thin film device is a promising candidates for CMOS compatible and high-density RRAM devices.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.35-35
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• 2003

Recent progress in the integration of the ferroelectric random access memories (FRAM) has attracted much interest. Strontium bismuth tantalate(SBT) is one of the most attractive materials for use in nonvolatile-memory applications due to low-voltage operations, low leakage current, and its excellent fatigue-free property. High-density FRAMs operated at a low voltage below 1.5V are applicable to mobile devices operated by battery. SBT films thinner than 0.1 #m can be operated at a low voltage, because the coercive voltage (Vc) decreases as the film thickness is reduced. In addition, the thickness of the SBT film will have to be reduced so it can fit between adjacent storage nodes in a pedestal type capacitor in future FRAMs.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기물성,응용부문
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• pp.103-104
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• 2006

$Pb(Zr,Ti)O_3(PZT)$ is very attractive ferroelectric materials for ferroelectric random access memory (FeRAM) applications because of its high polarization ability and low process temperature. However, Chemical Mechanical Polishing (CMP) pressure and velocity must be carefully adjusted because FeRAM shrinks to high density devices. The contaminations such as slurry residues due to the absence of the exclusive cleaning chemicals are enough to influence on the degradation of PZT thin film capacitors. The surface characteristics of PZT thin film were investigated by the change of process parameters and the cleaning process. Both the low CMP pressure and the cleaning process must be employed, even if the removal rate and the yield were decreased, to reduce the fatigue of PZT thin film capacitors fabricated by damascene process. Like this, fatigue characteristics were partially controlled by the regulation of the CMP process parameters in PZT damascene process. And the exclusive cleaning chemicals for PZT thin films were developed in this work.

• 한국세라믹학회지
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• 제42권9호
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• pp.624-630
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• 2005

To investigate the possibility of the $ZrO_2$ buffer layer as the insulator for the Metal-Ferroelectric-Insulator-semiconductor (MFIS) structure, $ZrO_2$ and $SrBi_2Ta_2O_9$ (SBT) thin films were deposited on the P-type Si(111) wafer by the R.F. magnetron-sputtering method. According to the process with and without the post-annealing of the $ZrO_2$ buffer layer and SBT thin film, the diffusion amount of Sr, Bi, Ta elements show slight difference through the Glow Discharge Spectrometer (GDS) analysis. From X-ray Photoelectron Spectroscopy (XPS) results, we could confirm that the post-annealing process affects the chemical binding condition of the interface between the $ZrO_2$ thin film and the Si substrate. Compared to the MFIS structure without the post-annealing of the $ZrO_2$ buffer layer, memory window value of MFlS structure with post-annealing of the $ZrO_2$ buffer layer were considerably improved. The window memory of the Pt/SBT (260 nm, $800^{\circ}C)/ZrO_2$ (20 nm) structure increases from 0.75 to 2.2 V under the applied voltage of 9 V after post-annealing.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.404-407
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• 2003

Among the ferroeletric thin films that have been widely investigated for ferroelectric random access memory (FRAM) applications, the $SrBi_2Ta_2O_9$ (SBT) thin film is appropriate as a memory capacitor material due to its excellent fatigue endurance. SBT thin films were etched in high-density $Cl_2/Ar$ in inductively coupled plasma. The maximum etch rate of SBT film is $1834\;{\AA}/min$ under $Cl_2/(Cl_2+Ar)$ of 30 %, rf power of 700 W, dc-bias voltage of -250 V, chamber pressure of 11 mTorr and gas flow rate of 20 sccm.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2000년도 추계학술대회논문집
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• pp.29-32
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• 2000

Cerium oxide thin film has been proposed as a buffer layer between the ferroelectric film and the Si substrate in Metal-Ferroelectric-Insulator-Silicon (MFIS ) structures for ferroelectric random access memory (FRAM) applications. In this study, CeO$_2$thin films were etched with Cl$_2$/Ar gas combination in an inductively coupled plasma (ICP). The highest etch rate of CeO$_2$film is 230 $\AA$/min at Cl$_2$/(Cl$_2$+Ar) gas mixing ratio of 0.2. This result confirms that CeO$_2$thin film is dominantly etched by Ar ions bombardment and is assisted by chemical reaction of Cl radicals. The selectivity of CeO$_2$to YMnO$_3$was 1.83. As a XPS analysis, the surface of etched CeO$_2$thin films was existed in Ce-Cl bond by chemical reaction between Ce and Cl. The results of XPS analysis were confirmed by SIMS analysis. The existence of Ce-Cl bonding was proven at 176.15 (a.m.u.).

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2000년도 추계학술대회논문집
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• pp.21-24
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• 2000

Ferroelectric YMnO$_3$thin films are excellent dielectric materials for high integrated ferroelectric random access memory (FRAM) with metal-ferroelectric-silicon field effect transistor (MFSFET) structure. In this study, YMnO$_3$thin films were etched with Cl$_2$/Ar gas chemistries in inductively coupled plasma (ICP). The maximum etch rate of YMnO$_3$thin films is 285 $\AA$/min under Cl$_2$/Ar of 10/0, 600 W/-200 V and 15 mTorr. The selectivities of YMnO$_3$over CeO$_2$and $Y_2$O$_3$are 2.85, 1.72, respectively. The results of x-ray photoelectron spectroscopy (XPS) reflect that Y is removed dominantly by chemical reaction between Y and Cl, while Mn is removed more effective by Ar ion bombardment than chemical reaction. The results of secondary ion mass spectrometer (SIMS) were equal to these of XPS. The etch profile of the etched YMnO$_3$film is approximately 65$^{\circ}$and free of residues at the sidewall.