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Ferroelectric Devices

IP.com Disclosure Number: IPCOM000078445D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Jacobs, JT: AUTHOR [+3]

Abstract

In thin-ferroelectric films sandwiched between metal electrodes, if a small area is poled to a given polarization value, it has been found that the stored Polarization decays with time. The reason for the decay of polarization is the presence of depolarization fields. These fields arise primarily from distribution of the compensating charges away from the metal ferroelectric interface, or from having dissimilar metals for top and bottom contacts with the ferroelectric. In the first case, the depolarization field will attempt to reduce the polarization at the poled spot. In the second case, dissimilar metals give rise to a built-in field due to the work function difference of the metals. This type of field tends to polarize the ferroelectric in a direction dictated by the built-in fields.

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Ferroelectric Devices

In thin-ferroelectric films sandwiched between metal electrodes, if a small area is poled to a given polarization value, it has been found that the stored Polarization decays with time. The reason for the decay of polarization is the presence of depolarization fields. These fields arise primarily from distribution of the compensating charges away from the metal ferroelectric interface, or from having dissimilar metals for top and bottom contacts with the ferroelectric. In the first case, the depolarization field will attempt to reduce the polarization at the poled spot. In the second case, dissimilar metals give rise to a built-in field due to the work function difference of the metals. This type of field tends to polarize the ferroelectric in a direction dictated by the built-in fields.

A method of improving the retention of polarization in thin-ferroelectric films and related devices is described below. This is accomplished by depositing a thin film of insulator materials such as SiO(2) or Si(3)N(4), upon the ferroelectric. The insulator is chosen so that its band-gap is larger than that of the ferroelectric. The thickness of the insulator is chosen such that when a voltage is applied to the structure, the charge flows through the oxide by tunneling. The compensation charge then resides at the ferroelectric-insulator interface in the ferroelectric.

After the switching of the ferroelectric is completed and the system is brought to a standby state, the only field present is the depolarizing field. Only a fraction of the field appears across the oxide which is of sufficient thickness to prevent the compensation charge leaving the ferroelectric, giving rise to approved retention. This effect may be utilized in ferroelectric photoconductive devices, ferroelectric field-effect transistor memory device applications, and fo...