The WT1 gene encoding a zinc finger polypeptide is a tumor suppressor gene that plays a key role in the carcinogenesis of Wilms' tumor. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to examine relative levels of WT1 gene expression (defined in K562 cells as 1.00) in 45 patients with acute myelogenous leukemia (AML), 22 with acute lymphocytic leukemia (ALL), 6 with acute mixed lineage leukemia (AMLL), 23 with chronic myelogenous leukemia (CML), and 24 with non- Hodgkin's lymphoma. Significant levels of WT1 gene were expressed in all leukemia patients and for CML the levels increased as the clinical phase progressed. In striking contrast with acute leukemia, the levels of WT1 gene expression for NHL were significantly lower or even undetectable. Clear correlation was observed between the relative levels of WT1 gene expression (< 0.6 v > or = 0.6) and the prognosis for acute leukemia (AML, ALL, and AMLL). Patients with less than 0.6 levels had significantly higher rates of complete remission (CR), disease-free survival, and overall survival than those with > or = 0.6 levels, whereas CR could not be induced in any of the 7 patients with acute leukemia having greater than 1.0 levels of WT1 gene expression. The quantitation of the WT1 gene expression made it possible to detect minimal residual disease (MRD) in acute leukemia regardless of the presence or absence of tumor-specific DNA markers. Continuous monitoring of the WT1 mRNA was performed for 9 patients with acute leukemia. In 4 patients, MRD was detected 2 to 8 months before clinical relapse became apparent. In 2 other patients, the WT1 mRNA gradually increased after discontinuation of chemotherapy. No MRD was detected in the remaining 3 patients with AML who received intensive induction and consolidation therapy. Simultaneous monitoring of MRD by RT-PCR using primers for specific DNA markers in 3 patients (2 AML-M3 with PML/RAR alpha, and 1 AML-M2 with AML1/ETO) among these 9 patients detected MRD comparable with that obtained from quantitation of WT1 gene expression. In a patient with acute promyelocytic leukemia, the limits of leukemic cell detection by RT-PCR using either WT1 or promyelocytic leukemia/retinoic acid receptor-alpha gene primers were 10(-3) to 10(- 4) and 10(-4) for bone marrow, and 10(-5) and 10(-4) for peripheral blood, respectively. Therefore, we conclude that WT1 is a new prognostic factor and a new marker for the detection of MRD in acute leukemia.

Retention characteristics of metal-ferroelectric-insulator-semiconductor (MFIS) structures have been studied theoretically by considering effects of charge injections derived from the difference between leakage current densities in the ferroelectric and insulator layers. The calculated curves for time-dependent capacitance have shown good agreements with experimental results. The numerical results for the MFIS structure have indicated that excess current over a certain value through the ferroelectric and the insulator layers causes the retention time to rapidly degrade. An idea of inserting an insulator film between the metal and the ferroelectric layers in an MFIS has also been examined in order to cut down the currents through the ferroelectric layer. The calculations based on our model have found this metal-insulator-ferroelectric-insulator-semiconductor (M-I-FIS) structure to exhibit much longer retention time than the conventional MFIS.

Preferentially (105)-oriented Sr0.7Bi2.8Ta2O9(SBTO) thin films on SiO2/n-Si(100) have been prepared by a pulsed laser deposition method at temperatures as low as 350°C, which is the lowest process temperature for growing SBTO ferroelectric thin films. Dielectric properties of SBTO films have been improved by increasing the Sr/Bi atomic ratio from 0.7/2.8 to 0.7/2.0. A memory window as large as 3.6 V in the Metal-Ferroelectric-Insulator-Semiconductor(MFIS) capacitor has been obtained at a Sr/Bi ratio of 0.7/2.0. This is the largest value among the MF(I)S diode structures. Little degradations in C-V are observed up to fatigue of over 1010 cycles for a process temperature of 400°C, or especially for Sr/Bi of 0.7/2.0, keeping the memory window at more than 3.2 V. It should be emphasized that improvement in memory characteristics is strongly related to the insulating properties of the ferroelectric and dielectric thin films rather than to the value of the dielectric constant.

Metal-ferroelectric-insulator-semiconductor (MFIS) structures using silicon nitride (SiNx) and silicon oxynitride (SiON) layers as an insulating barrier against interdiffusion have been proposed and investigated. SrBi2Ta2O9 (SBT) films are deposited as ferroelectric layers by pulsed laser deposition (PLD) method on SiNx/SiO2/Si and SiON/Si substrates at low temperatures. An Al/SBT/SiNx/SiO2/Si (MFNOS) structure exhibits a larger memory window and a smaller shift in C–V curve than those of the Al/SBT/SiO2/Si structure. Moreover, strong barrier effect of SiNx layer is demonstrated by both Rutherford back scattering spectroscopy (RBS) analysis and comparison of two Al/SiNx/SiO2/Si structures with and without depositing SBT film. An Al/SBT/SiON/Si (MF(ON)S) structure also shows good C–V characteristics with no degradation in the curve gradient. In addition, the C–V curve shows no change when the sweep rate of the bias voltage is increased from 0.2 V/s to 40 kV/s, which indicates that the hysteresis originates not from ion drift but from high-speed ferroelectric polarization.

A stable micro second harmonic generation (SHG) laser consisting of a diode- pumped Nd:YVO4 laser doubled by KTiOPO4 achieves 3 times higher storage density than usual on an erasable optical disk.