This paper reports an active phase shifter circuit implemented with discrete components and which uses a ferroelectric capacitor as the tuning element. The circuit IF consists of two bipolar transistors coupled with a feedback network that has a voltage variable transfer function. The active nature of the circuit allows for signal gain, while the ferroelectric varactor provides a high-Q tuning element. Thus, the overall performance is improved by the advantages of both technologies. Computer simulations with measured results from the implemented system are presented and show that the network, even with markedly non-ideal transistors, can provide a true all-pass response over the frequency band of interest (100-500 MHz). The measurement results demonstrate an analog tunability of about 140 degrees with a gain variation of about 1 dB at 300 MHz when using a Ba0.5Sr0.5TiO3 (BST) capacitor with a tunability of 2:1.

ABSTRACT In this work we announce a ferroelectric charge transfer device that uses a high-k buffer layer underneath the ferroelectric layer as a tunnel oxide, where the high electric field required for Fowler-Nordheim charge tunneling through the buffer layer is provided by the polarized ferroelectric. This device exhibits data retention of 10 years at room temperature while retaining the properties of fast write and low voltage operation. Since the electric field across a buffer layer due to the ferroelectric polarization surface charge is ∼E = P r /ϵ0 ϵ ox then with Pr on the order of 10 μ C/cm2 and ϵ ox for a high k dielectric is ∼20, we have an electric field of 5.6 MV/cm which is sufficient to generate significant tunnel currents across a high–k buffer layer. Charges tunneling from the Si substrate are trapped in the interface between the high-k buffer and the ferroelectric and only detrap thermally; this leads to the long data retention observed on these devices. Despite the fact that charge transfer is accomplished by tunneling, a relatively slow process, this device can be programmed or erased in only the time it takes to switch the ferroelectric, which is of the order of nanoseconds.

YMnO3 thin films were studied on Pt/Ti/SiO2/Si as a candidate for ferroelectric transistor random access memory (FeTRAM). The films were deposited by flash-evaporated metalorganic chemical vapor deposition (MOCVD) at low temperature and post annealed to crystallize the films to form a c-axis oriented hexagonal phase. Polarization versus electric field measurements on metal/ferroelectric/metal capacitors shows a remnant polarization of about 2 μC/cm2 and a coercive field of approximately10 kV/cm. Fatigue stress cycling shows no degradation of films up to 1011 cycles.

Perovskite ferroelectric thin films in the paraelectric state exhibit outstanding dielectric properties, even at high frequencies (>1 GHz). The tunable dielectric constant of ferroelectric thin films can be used to design frequency and phase agile components. High dielectric constant thin film ferroelectric materials in the paraelectric state have received enormous attention due to their feasibility in applications such as decoupling capacitors and tunable microwave capacitors; the latter application has been fueled by the recent explosion in wireless and satellite communications. This paper reportsBa0.96Ca0.04Ti0.84Zr0.16O3 (BCTZ) thin films that were deposited on Pt electrodes using radio frequency magnetron sputtering at a low (450 °C) substrate temperature. Sputtered thin film BCTZ at low substrate temperature is compatible with conventional integrated circuit technology. The structural characterization of the deposited films was performed by x-ray diffraction. The electrical characterization of the films was achieved by capacitance-voltage, current-voltage, and S-parameter (via vector network analyzer) measurements. In addition, the effect of post annealing on the deposited films was investigated. A detailed understanding of both their processing and material properties is discussed for successful implementation in high frequency applications.

Ba 0.96 Ca 0.04 Ti 0.84 Zr 0.16 O 3 (BCTZ) and Ba0.5Sr0.5TiO3 (BST) thin films were deposited at a substrate temperature of 450°C via rf magnetron sputtering to form Pt∕BCTZ∕Pt and Pt∕BST∕Pt capacitors. BCTZ thin films hold promise as an alternative to BST in capacitor applications due to the resistance of BCTZ to reducing atmospheres. In order to produce BST films with low dc leakage current, oxygen is routinely used during film growth and often afterwards during anneals. The effect of postannealing the capacitors in either forming gas or oxygen at temperatures up to 700°C (BST) and 800°C (BCTZ) were studied. The leakage mechanism is shown to be dominated by Schottky emission and the Schottky barrier height is reported as a function of anneal gas composition and anneal temperature.

This paper describes an active phase shifter with a large amount of variable phase. We propose a design that has second-order all-pass network characteristics and that uses a tunable ferroelectric capacitor. The transmitted phase is changed by varying the capacitance of a ferroelectric capacitor. A computer simulation is presented that shows that the network, even with markedly non-ideal transistors, can provide a true all-pass response over the frequency band of interest (100 MHz–400 MHz). These simulated results demonstrate an analog tunability of about 200° with a gain variation of about 3 dB at 300 MHz—when using a Ba0.96Ca0.04Ti0.84Zr0.16O3 (BCTZ) capacitor with a tunability of 2:1. The simulation performed at 300 MHz because the physical layout of the real life circuit will be done mostly with the discrete components. As the self resonance frequency of most of the discrete components lies in the few hundreds of MHz range, our preferred frequency is a practical one to deal with. The simulation also predicts a flat band gain of approximately 10 dB with ± 2 dB of gain ripple.

Yttrium manganate (YMO) thin films were prepared on SiO2 buffered silicon as a candidate for ferroelectric transistor random access memory (FeTRAM). The films were deposited by flash evaporated MOCVD at low temperature and post annealed to crystallize the c-axis oriented hexagonal YMO phase. It is found that oxygen content and substrate temperature are major parameters determining c-axis orientation. For the electrical characteristics, P-r (remnant polarization) similar to2 muC/cm(2) and epsilon (dielectric constant) similar to20 are obtained in Pt/YMO/Pt structures. It is also found that a top buffer layer of 30 nm ZrO2 helps to reduce the leakage current of Pt/top buffer/YMO/SiO2/Si stack to 10(-7) A/cm(2) and improves the C-V memory window from 0.2 V to 2 V.