High-dielectric thin films have attracted great interests as DRAM dielectric materials because of their high dielectric constant, but the electrical properties related to DRAM operation such as dielectric relaxation and conduction leakage properties have not sufficiently studied yet. Dielectric relaxation phenomena are observed with the dielectric relaxation current in the time domain or with the dielectric dispersion in the frequency domain. The dielectric relaxation and the dielectric dispersion are fundamentally the same because it is verified that they are connected each other through Fourier integral transform. The dielectric relaxation of high dielectric thin films such as SrTi$O_3$, (Ba,Sr)Ti$O_3$, Pb(Zr,Ti)$O_3$ is known to be Curie-von Schweidler relaxation. Waser et al. and Horikawa et al. proposed a multiple series connected RC circuit could be an equivalent circuit of Curie-von Schweidler relaxation.
We have been tried to make an equivalent circuit model of Curie-von Schweidler relaxation. In the progress of circuit-modeling, we have developed a new method to determine the RC parameters utilizing a distribution function of relaxation times. It has been verified that the developed distribution function of relaxation times is that of Curie-von Schweidler relaxation. By approximating the continuous distribution function to multiple delta functions which are the distribution functions of Debye relaxation, we could change the distribution function of Curie-von Schweidler relaxation to that of multiple Debye relaxation. Each Debye relaxation can be converted to a series connected RC circuit. As the same way, the Curie-von Schweidler relaxation can be converted to an equivalent circuit.
We have verified that the modeled equivalent circuit has a characteristic very close to that of Curie-von Schweidler relaxation in the time and the frequency domain. Furthermore, with the equivalent circuit, the effect of the dielectric relaxation on DRAM operation has been simulated. The current conduction properties of the high dielectric capacitor has been modeled with a linear resistor and its effect have been also simulated.
Finally, we have tried to measure the frequency response of (Ba,Sr)Ti$O_3$ thin film capacitor as a new method to investigate the dielectric relaxation of high dielectric capacitor. In this process, a new fabrication process has been developed and an easy de-embedding procedure for parasitic components has been introduced. Low frequency response of the fabricated high dielectric capacitor has been measured with an impedance analyzer and the high frequency response has been measured with a network analyzer up to 1GHz. The (Ba,Sr)Ti$O_3$ thin film capacitor showed high dielectric properties up to 1GHz. The measured dielectric properties are believed to be sufficient for DRAM application. The measured dielectric properties are believed to be sufficient for DRAM application. With the measured frequency response of the high dielectric capacitor, an equivalent circuit has been realized and it was found that the characteristics of the equivalent circuit are very close to the measured characteristics of the dielectric capacitor in the time domain and the frequency domain. This result implies that the developed procedure for the equivalent circuit of the Curie-von Schweidler relaxation is a very effective and useful method.
