Ferroelectric memory devices typically include one or more arrays of ferroelectric capacitors that are used as data storage elements. A ferroelectric capacitor typically includes a dielectric formed from a ferroelectric material, disposed between respective conductive "plate" and "storage" electrodes. When a sufficient voltage is applied across the electrodes of the ferroelectric capacitor, the ferroelectric material exhibits a persistent polarization wherein the dipoles of the ferroelectric material arrange themselves along in a predetermined direction. This polarization state remains even when the applied electric field is removed. Thus, ferroelectric capacitors can and have been used as data storage devices.
A typical hysteresis characteristic for a ferroelectric capacitor is shown in FIG. 1, in which the horizontal axis represents a voltage applied across the electrodes of a ferroelectric capacitor, and the vertical axis represents polarization of the ferroelectric dielectric of the capacitor. As illustrated in FIG. 1, polarization of a ferroelectric dielectric occurs according to a predetermined hysteresis loop. When a positive voltage applied to the ferroelectric-dielectric film reaches a predetermined magnitude (point B), a positive polarization +Pm is induced. When the voltage applied to the dielectric is decreased to 0V, the ferroelectric dielectric remains positively polarized at a positive remnant polarization +Pr (point C). If the applied voltage is then sufficiently decreased (point D), a polarization reversal is induced, producing a negative polarization -Pm. Then, when the applied voltage is increased to 0V, the ferroelectric dielectric remains negatively polarized at a negative remnant polarization -Pr (point A). If the applied voltage is sufficiently increased (point B), the ferroelectric dielectric will undergo another polarization reversal back to a positive polarization state (point B).
Conventional processes for testing ferroelectric memory devices typically include a direct current (DC) test that tests the operation of input/output protection circuits connected to the ferroelectric capacitor memory array. This DC test typically is followed by an alternating current (AC) test that tests the polarization characteristics of the ferroelectric capacitors, as well as operation of associated peripheral circuits such as sense amplifiers. This AC test typically requires a long time to complete.
USPTO Backgrounds
USPTO Backgrounds