Both BiFeO3/Bi3.15Nd0.85Ti3O12 (BNdT) bi-layers and BiFeO3 thin films were grown on Pt/Ti/SiO2/Si by the sol–gel method. While just a nearly linear dielectric response was observed in the BiFeO3 film, the BiFeO3/BNdT bi-layers exhibited a saturated ferroelectric hysteresis loop with a large remanent polarization (2Pr = 72 µC cm−2). This 2Pr value is also much higher than that (∼20 µC cm−2 reported previously) of BNdT films. The large remanent polarization of bi-layers results dominantly from the giant polarization of the BiFeO3 layer performed under an actual field of 607.4 kV cm−1 when the BNdT layer acts as an insulating barrier, leading to almost a ten times increase in the breakdown field of the BiFeO3 layer.

We report on the use of amorphous Ni-Al film ͑a-Ni-Al͒ as conductive diffusion barrier layer to integrate La 0.5 Sr 0.5 CoO 3 / PbZr 0.4 Ti 0.6 O 3 /La 0.5 Sr 0.5 CoO 3 capacitors on silicon. Cross-sectional observation by transmission electron microscope reveals clean and sharp interfaces without any discernible interdiffusion/reaction in the sample. The physical properties of the capacitors are vertically characterized as the parameters of memory elements. Excellent ferroelectric properties, e.g., large remnant polarization of ϳ22 C/cm 2 , small coercive voltage of ϳ1.15 V, being fatigue-free, good retention characteristic, imply that amorphous Ni-Al is an ideal candidate for diffusion barrier for the high-density ferroelectric random access memories integrated with silicon transistor technology. microelectromechanical systems ͑MEMS͒, 7-9 and pyroelectric sensors.10 Currently, great efforts have been intensively made to integrate PZT based ferroelectric capacitors with modern silicon transistor technology to yield one-transistorone-capacitor ͑1T-1C͒ based memory architectures 2 in order to realize high-density ferroelectric random access memories. In such a memory cell, the drain must be electrically in contact with the bottom electrode of ferroelectric capacitor stack. If the PZT ferroelectric capacitor stack is directly integrated on Si, however, the chemical reactions and interdiffusion between the bottom electrode and silicon may generate a nonconducting layer, resulting in the failure of the memory cell due to the deterioration of the electric contact between the bottom electrode and silicon. To solve this problem, an extra layer, usually called "diffusion barrier layer," is interposed between PZT capacitor stack and Si wafer to separate them from direct contact. Ideally the diffusion barrier should possess a nature of good oxidation resistance, high thermal and chemical stabilities and large electrical conductivity ͑so as to function as a bridge to conduct electric current between its bordering layers͒. In literature, several intermetallic systems such as Pt-͑Ti,Al͒N and Ir-TiN were investigated for the use of barriers.7,11-13 While these materials possess very high electrical and thermal conductivities, there are still some concerns such as the formation of Pt hillock structure due to the stress release in the processing, the difficulty in developing a reliable reactive ion etching process for the refractory metals, and the inherently high cost.14 To find alternative material systems is thus an active topic in recent years. Among several candidates, amorphous Ni-Al seems to be a good choice because it is highly resistant to oxidation, low cost, and ready to be patterned by conventional etching techniques. In this letter, we report the integration and characterization of a ferroelectric heterostructure La 0.5 Sr 0.5 CoO 3 /Pb Zr 0.4 Ti 0.6 O 3 /La 0.5 Sr 0.5 CoO 3 on highly doped silicon using amorphous Ni-Al thin film as the conductive diffusion barrier layer ͑the whole structure is abbreviated as LSCO/...

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Ultrathin amorphous Ni–Ti film is investigated as conductive diffusion barrier layer to integrate La0.5Sr0.5CoO3∕PbZr0.4Ti0.6O3∕La0.5Sr0.5CoO3 (LSCO/PZT/LSCO) capacitors on silicon. X-ray photoelectron spectroscopy results demonstrate that Ni in LSCO∕Ni–Ti∕Si heterostructure is not oxidized after 550°C annealing in oxygen. The structural properties of LSCO∕PZT∕LSCO∕Ni–Ti∕Si are characterized by x-ray diffraction and transmission electron microscopy. It is found that Ni–Ti film is still amorphous and that there are no discernible reactions at the interfaces of the sample. LSCO/PZT/LSCO capacitor, measured at 5V, possesses very good ferroelectric properties, such as low coercive field (∼1.28V), high remnant polarization (∼27.9μC∕cm2), and good fatigue-free characteristic, implying that ultrathin amorphous Ni–Ti film can be used as barrier layer for fabricating high-density ferroelectric random access memories.

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