Liquid crystal display device having two metastable states and its driving method

Claim 2

A liquid crystal display device having a chiral nematic liquid crystal sandwiched between a pair of transparent electrode substrates equipped with liquid crystal alignment layers, where said chiral nematic liquid crystal has a twisted structure of twist angle φ in its initial state and has two metastable states different from said initial state as relaxation states after the voltage that brings about a Frederick's transition in said initial state is applied, wherein a voltage applied to bring about the Frederick's transition is a voltage pulse greater than the threshold value in the initial state and the two metastable states, a voltage applied to select one of the two metastable states is a voltage pulse selected using the critical value that generates one of the two metastable states as a reference, and a voltage applied during a period the selected metastable state is to be maintained is a voltage pulse lower than the threshold value in the two metastable states.

Claim 3

The liquid crystal device of claim 1 or 2 wherein the angles (ϑ ₁ , ϑ ₂ ) formed by the director vectors at the interfaces between the liquid crystal and each of the liquid crystal alignment layers, with the respective surface of the pair of transparent electrode substrates in the initial state have opposite signs.

Claim 4

The liquid crystal display device of claim 1, 2 or 3 wherein of the twist angles of the liquid crystal molecules in the two metastable states, one is φ-180 degrees and the other is φ+180 degrees.

Claim 5

The liquid crystal display device of claims 3 and 4 wherein the device has plural critical values and the metastable state having a twist angle of φ+180 degrees is selected when the absolute value of the voltage pulse applied to select one of the metastable states is below the critical value of the lowest absolute value.

Claim 6

The liquid crystal display device of claims 3 and 4 wherein the device has plural critical values and the metastable state having twist a angle of φ-180 degrees is selected when the absolute value of the voltage pulse applied to select one of the metastable states is a value between the critical value of the lowest absolute value and the critical value of the next lowest absolute value.

Claim 7

The liquid crystal display device of any one of the preceding claims 1 wherein a scanning electrode group and a signal electrode group are disposed on the pair of transparent electrode substrates, respectively, and the picture elements comprising those respective groups are driven by time-shared addressing.

Claim 8

The liquid crystal display device of any one of the preceding claims wherein the voltage pulse to bring about the Frederick's transition is applied in a first period, the voltage pulse to select one of the two metastable states is applied in a subsequent second period, and the voltage pulse to maintain a selected one of the metastable states is applied during a third period.

Claim 9

The liquid crystal display device of claim 8 wherein the twist angle of the liquid crystal molecules in a metastable state is φ+180 degrees when the absolute value of the voltage pulse in the second period is between zero and the critical value.

Claim 10

The liquid crystal display device of claims 7 and 8 wherein the selection period in time-shared addressing is the first period and second period and the nonselection period is the third period.

Claim 11

The liquid crystal display device of claims 7 and 8 wherein the selection period in time-shared addressing is the second period and the nonselection period is the third period and the first period.

Claim 12

The liquid crystal device of claims 7 and 8 wherein all picture elements have a first period and a second period before undergoing time-shared addressing.

Claim 13

The liquid crystal device of claim 12 wherein all picture elements have the same twist angle before undergoing time-shared addressing, namely φ-180 degrees or φ+180 degrees.

Claim 14

The liquid crystal device of claim 12 wherein all picture elements have a first period and a second period simultaneously.

Claim 15

The liquid crystal device of claim 12 wherein all picture elements have a first period and a second period sequentially every plural number of scanning electrodes.

Claim 16

The liquid crystal device of claim 12 wherein all picture elements have plural first periods and second periods.

Claim 17

The liquid crystal device of claim 7 and 8 wherein in the scanning electrode group, an integer number n of scanning electrodes is divided up into blocks each block comprising an integer number k (k ≦ n) of scanning electrodes and each block is line-sequentially scanned such that each screen is time-shared n/k times.

Claim 18

The liquid crystal device of claims 7 and 8 wherein only the scanning electrodes including picture elements that must be rewritten after the scanning electrodes are scanned in one cycle are provided with a first period and a second period and are driven by time-shared addressing.

Claim 19

Driving method for a liquid crystal display device that sandwiches chiral nematic liquid crystal between a pair of transparent electrode substrates equipped with liquid crystal alignment layers, where said chiral nematic liquid crystal has a twisted structure in its initial state and has two metastable states different from said initial state as relaxation states after the voltage that brings about a Frederick's transition in said initial state is applied, wherein after the Frederick's transition is brought about, one of the metastable states is generated by applying the voltage pulse whose absolute value is selected using the critical value that generates one of the metastable states as a reference, after which the selected metastable state is maintained by applying the voltage pulse below the threshold value in the two metastable states.

Claim 20

The driving method for a liquid crystal display device of claim 19 wherein a scanning electrode group and a signal electrode group are disposed on the pair of transparent electrode substrates, respectively, and the picture elements comprising those respective groups are driven by time-shared addressing.

Claim 21

The driving method for a liquid crystal display device of claim 20 wherein Frederick's transition is brought about and one of the metastable states is selected in the selection period in time-shared addressing and the selected metastable state is maintained in the nonselection period.

Claim 22

The driving method for a liquid crystal display device of claim 20 wherein one of the metastable states is selected in the selection period in time-shared addressing and the selected metastable state is maintained and Frederick's transition is brought about in the nonselection period.

Claim 23

The driving method for a liquid crystal display device of claim 20 wherein Frederick's transition is brought about for all picture elements and one of the metastable states is selected before time-shared addressing.