Metal-ferroelectric-semiconductor Research Articles

Electrical properties of ferroelectric-capacitor-gate si mos transistors using p(l)zt films

A ferroelectric-capacitor-gate Si MOSFET which consists of an SiO2/Si MOSFET and a ferroelectric capacitor has been demonstrated. It is shown that memory functions can be obtained by connecting the ferroelectric capacitor with the gate of MOSFETs. The operation of such devices is similar to that of metal-ferroelectric-semiconductor (MFS) FETs. The large memory window or threshold voltage shift can be obtained with a ferroelectric capacitor which has a large coercive voltage. The memory effect of the device has been demonstrated by showing the drain current change by a previously applied “write” pulse at a fixed gate voltage of 0V.

Ferroelectric Properties of BaMgF4 Films Grown on Si(100), (111), and Pt(111)/SiO2/Si(100) Structures

Ferroelectric properties of BaMgF4 (BMF) films grown on Si(100), (111) and Pt(111)/SiO2/Si(100) structures were studied. No ferroelectric polarization along the surface normal was observed for (011)-oriented BMF films grown on Si(100) substrates, while (120)-oriented BMF films grown on Si(111) and Pt(111)/SiO2/Si(100) structures clearly showed hysteresis characteristics with ferroelectric polarization. The remanent polarization values of the BMF films on Si(111) and Pt(111)/SiO2/Si(100) structures were 0.89 µC/cm2 and 5.0 µC/cm2, respectively. Fabrication and characterization of metal-ferroelectric-semiconductor (MFS) field effect transistors (FETs) using Si(111) substrates were attempted. It was observed that the threshold voltage of the fabricated MFS FETs was shifted upon applying a gate voltage.

Pt/PZT/n-SrTiO3 Ferroelectric Memory Diode

We fabricated a new nonvolatile ferroelectric memory, which consists of vertical metal-ferroelectric- semiconductor diodes. Our diode has a simpler structure than an Ferroelectric Random Access Memory (FRAM) cell, and operates at a lower voltage than Metal Ferroelectric Semiconductor Field Effect Transistors (MFS-FETs) or conventional flash memories. We demonstrated the memory operation using a Pt/PZT/n- SrTiO3 diode in this work. We deposited (001)-oriented PZT on (100) 0.5 wt% Nb doped n-type SrTiO3 substrate using a laser ablation technique. The diodes had a hysteresis loop in their capacitance-voltage characteristics due to ferroelectric polarization in the PZT layer. Their current-voltage curves were Schottky-diode-like and also had a hysteresis loop due to the ferroelectric remanent polarization. We confirmed correct nonvolatile and nondestructive memory readout operation. The write voltages were -5 V to write a logic “0” and above 2.5 V to write a logic “1”. The read voltage was 0.8 V.

Electrical Properties of Lead Lanthanum Titanate Thin-Film Capacitors Prepared by Sol-Gel Method

High-quality (Pb1-x Lax )Ti1-x /4O3 (x=0.05) [PLT] thin films were fabricated successfully by sol-gel processing onto Pt/Ti/SiO2/Si and p-Si substrates. The optimum route and the conditions for preparing homogeneous and crack-free thin films were systematically investigated. Ferroelectric perovskite phase was observed in the PLT thin films annealed at 600° C for 30 min. We studied the electrical properties of the PLT film capacitors with the metal-ferroelectric-metal (MFM) and the metal-ferroelectric-semiconductor (MFS) structure for use in ferroelectric memories. The dielectric constant and dissipation factor measured for MFM capacitor were 225 and 0.018 at 100 kHz, respectively. The remanent polarization (P r) and coercive field (E c) of the PLT film were 8.5 µC/cm2 and 110 kV/cm, respectively. Also the film with 600 nm thickness showed current density as low as 10-6 A/cm2 at the electric field of 200 kV/cm, which corresponds to the electric resistivity of ∼1012 (Ω·cm) and represents excellent insulating properties. The MFS capacitor showed ferroelectric switching properties in C-V characteristics and the memory window of the hysteresis loop was about 1 V in the operation of ±10 V.

Adaptive-learning neuron circuits using ferroelectric thin films

Abstract Adaptive-learning neuron circuits are reviewed, in which a pulse frequency modulation (PFM) system is used and the interval of output pulses is changed through the learning process. Key devices of the circuits are MFSFETs (Metal Ferroelectric Semiconductor Field Effect Transistors). They are used for representing the synaptic weights of neurons and the polarity of the films is gradually changed by applying input pulses to the gates. In order to produce PFM signals, circuit using a UJT (unijunction transistor) is discussed. As a preliminary experiment for realization of MFSFETs, the electrical properties of metal ferroelectric metal (MFM) capacitor using sol-gel derived PZT films are discussed.

Structural and electrical studies on rapid thermally processed ferroelectric Bi4Ti3O12 thin films by metallo-organic solution deposition

Thin films of Bi4Ti3O12 that were pinhole free with uniform composition and thickness were prepared by the metallo-organic solution deposition technique on platinum coated silicon and bare silicon substrates. Crack free and crystalline films of 5000 Å thickness were fabricated by spinning and post deposition rapid thermal annealing treatment at 500 °C. The films exhibited good structural, dielectric, and ferroelectric properties. The effects of annealing temperature and time on the structural and electrical properties of the films were evaluated. The measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 184 and 0.039, respectively for a film rapid thermally annealed at 700 °C for a time of 10 s. Room temperature resistivity of 108 Ω cm and leakage current density of less than 10−7 A/cm2 were obtained for a 0.5-μm-thick film at an applied electric field of 100 kV/cm; establishing good insulating behavior. Ferroelectricity was confirmed by P–E hysteresis loops with remanent polarization and coercive field values of 4.4 μC/cm2 and 84 kV/cm, respectively. The high frequency C–V measurements on films in metal–ferroelectric–semiconductor configuration indicated good Si/Bi4Ti3O12 interface characteristics. The films showed good switching endurance under bipolar stressing at least up to 1010 switching cycles.

Excimer laser ablated barium strontium titanate thin films for dynamic random access memory applications

Polycrystalline thin films of Ba0.5Sr0.5TiO3 were deposited by excimer laser (248 nm) ablation. Films deposited near 575 °C exhibited good crystallinity, a dielectric constant of 330, a dissipation factor of 0.02, a leakage current density of 2×10−7 A/cm2, a charge storage density of 36 fC/μm2, and breakdown time of 3700 s at an applied electric field of 0.125 MV/cm. The C-V (capacitance-voltage) behavior of both MFM (metal-ferroelectric-metal) and MFS (metal-ferroelectric-semiconductor) structures were studied and the estimated dielectric permittivity in the accumulation region of MFS structure nearly indicated the bulk value, suggesting a reasonably good Ba0.5Sr0.5TiO3/Si interface.

Metal-Ferroelectric-Semiconductor structures based on thin Sn2P2S6 films

Abstract Hysteresis effects in the metal-ferroelectric-semiconductor (MFS) structures composed of thin Sn2 P2 S6 films on silicon substrates with resistivity of 10 and 70 0hm·cm have been studied using the method of C-V characteristics, By varying the amplitude of the bias voltage one may observe changes in the character of the hysteresis of C-V characteristics permitting the specific features to be traced of the interaction between a bound charge of the ferroelectric film and the subsurface bulk charge of the semiconductor. In the structures of either type, two mechanisms of the hysteresis phenomena are manifested, namely, the polarization and the injection mechanism. Temperature effect on the hysteresis in YIPS structures has also been studied.

Electrical Characterization of Ferroelectric Thin Films of Lithium Niobate on Silicon Substrates

ABSTRACTThin films (.1-.6 μm) of LiNbO3 have been deposited on silicon substrates by rf reactive sputtering. MFS (metal-ferroelectric-semiconductor) capacitor structures were created by a liftoff process which physically isolated small areas of LiNbO3. Standard MOS (metal-oxide-semiconductor) electrical characterization techniques were used to determine the resistivity and dielectric constant of the films. Short-circuit photocurrent measurements revealed both transient and steady state components attributed to a pyroelectric effect and a bulk photovoltaic effect respectively. The conduction processes in these films were examined and found to exhibit Frenkel-Poole characteristics. Ferroelectric switching at room temperature has also been observed in these films, however, the reversed orientation was not stable.

Characterization of sputtered thin films of barium strontium titanate on silicon substrates

Abstract Thin films of barium strontium titanate were r.f. sputter deposited at various temperatures, gas pressures, and gas compositions on both p-type and n-type (111) and (100) silicon substrates. Ellipsometry techniques were used to determine thickness and refractive index, while X-ray Bragg diffraction was used to determine the degree of crystallinity and orientation. SEM was used to reveal surface morphology and domain structure. Semi-transparent gold electrodes were evaporated on the films, to facilitate electrical characterization. Capacitance vs. voltage, current vs. voltage, and photocurrent measurements were used to characterize the MFS (metal ferroelectric semiconductor) capacitor structures. From these tests, dielectric constant, resistivity, pyroelectric coefficient, and breakdown field were determined.

A study of electronic states near the interface in ferroelectric-semiconductor heterojunction prepared by rf sputtering of PbTiO3

Interface states in the ferroelectric-semiconductor junction have been investigated from analyses of DLTS andC-V data. Two trap levels are located at 0.21 and 0.36 eV below the conduction band near the silicon side of the interface in the MFS (Metal-Ferroelectric-Semiconductor) structure. The interface states density has been drastically reduced by putting an oxide layer between ferroelectric and semiconductor with certain heat treatment in H2 atmosphere at 500 °C. It has been found that the MFMOS (Metal-Ferroelectric-Metal-Oxide-Semiconductor) structure shows the least interface states density (less than 1011cm−2eV−1) with the maximal dielectric constant of PbTiO3 thin films.

“MFS FET” -A New Type of Nonvolatile Memory Switch Using PLZT Film

A step-like change in the interface built-in potential by controlling the ferroelectric polarization has been observed in PLZT thin film sputtered on GaAs single crystal heterostructure junction. We have developed a nonvolatile memory FET by using this MFS (Metal-Ferroelectric-Semiconductor) construction. A typical performance of the GaAs device with a p-channel mode operation is that the writing (“0” to “1” threshold) gate voltage Von=1.5 V, the erasing (“1” to “0”) gate voltage Voff=6.0 V, and the on state drain current Ion=0.1 mA. This operation power level obtained here is about one order of magnitude smaller than that of similar type devices using other ferroelectrics such as Bi4Ti3O12, PZBFN and SbSI. A series of technical data for the fabrication technologies including thin film deposition of the ferroelectric are presented, and the analyses on the device performance are also discussed.