1. A method for driving a piezoelectric ink jet head composed of:
a pressure chamber filled with an ink;
a nozzle that communicates with the pressure chamber and has an ink meniscus formed therein from the ink that fills the pressure chamber;
a piezoelectric element of transverse vibration mode that contracts in the direction of plane when subjected to a drive voltage applied thereto; and
an oscillator plate that is stacked on the piezoelectric element so as to constitute a drive section and deflects so as to decrease the volume of the pressure chamber as the piezoelectric element contracts in the direction of plane when a voltage is applied thereto, so as to pressurize the ink in the pressure chamber and discharge an ink droplet from the tip of the nozzle, and
wherein the piezoelectric ink jet head is operated by combining
(A) the step of applying a drive voltage to the piezoelectric element so that the piezoelectric element contracts in the direction of plane and the oscillator plate deflects, thereby decreasing the volume of the pressure chamber, and
(B) the step of removing the drive voltage applied to the piezoelectric element so that the contraction of the piezoelectric element in the direction of plane is canceled and consequently the deflection of the oscillator plate is canceled, thereby increasing the volume of the pressure chamber, thereby to discharge an ink droplet from the tip of the nozzle,
characterized in that the piezoelectric element is driven with a drive voltage waveform that has at least one of the following settings:
(a) time constant \u03c4UP of rise of the drive voltage in the process (A) is set in a range that satisfies the relation of the expression (i):
Ta(\u2212ln0.01)\u2266\u03c4UP\u2266Ta(\u2212ln0.25)\u2003\u2003(i)
with respect to the period Ta of the ensuing vibration of the drive section which is superposed on the vibration waveform of the volumetric velocity of ink in the head,
(b) time constant \u03c4DN of fall of the drive voltage in the process (B) is set in a range that satisfies the relation of the expression (ii):
Ta(\u2212ln0.01)\u2266\u03c1DN\u2266Ta(\u2212ln0.25)\u2003\u2003(ii)
with respect to the period Ta.
2. A method for driving the piezoelectric ink jet head of claim 1, wherein the piezoelectric ink jet head is operated as follows:
a constant drive voltage is continuously applied to the piezoelectric element during a period of standby so that the piezoelectric element is kept contracted in the direction of plane and the oscillator plate continues to deflect, thereby to maintain the pressure chamber in a state of decreased volume and, during a period of forming a dot,
(1) the drive voltage is removed immediately before forming the dot so as to cancel the contraction of the piezoelectric element and relieve the oscillator plate deflection, thereby increasing the volume of the pressure chamber and pulling the ink meniscus in the nozzle back toward the pressure chamber, then
(2) the drive voltage is applied again so as to cause the piezoelectric element to contract and the oscillator plate to deflect, thereby decreasing the volume of the pressure chamber and discharge an ink droplet through the tip of the nozzle.
3. A method for driving the piezoelectric ink jet head of claim 1, wherein the piezoelectric ink jet head is operated as follows:
the piezoelectric element in the state of standby is maintained in such a condition that drive voltage is not applied thereto, and
during a period of forming a dot,
(I) the drive voltage is applied immediately before forming the dot so as to cause the piezoelectric element to contract and the oscillator plate to deflect, thereby decreasing the volume of the pressure chamber, pushing the ink meniscus in the nozzle toward the tip of the nozzle and protruding the ink from the tip of the nozzle like a column, then
(II) the drive voltage is removed again so as to cancel the contraction of the piezoelectric element and cancel the deflection of the oscillator plate, thereby increasing the volume of the pressure chamber and pulling back the ink column that has been protruding from the tip of the nozzle into the nozzle, thereby separate an ink droplet.
4. A method for driving the piezoelectric ink jet head of claim 1, wherein the time constant \u03c4UP of rise of the drive voltage in the step (A) is set in a range defined by a relation of the expression (i-1):
Ta(\u2212ln0.05)\u2266\u03c4UP\u2266Ta(\u2212ln0.25)\u2003\u2003(i-1)
with respect to the period Ta.
5. A method for driving the piezoelectric ink jet head of claim 1, wherein the time constant \u03c4DN of fall of the drive voltage in the step (B) is set in a range that satisfies the relation of the expression (ii-1):
Ta(\u2212ln0.05)\u2266\u03c4DN\u2266Ta(\u2212ln0.25)\u2003\u2003(ii-1)
with respect to the period Ta.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A MOSFET comprising:
an active region of a first conductivity type provided on an insulating layer, the active region having a first portion and a second portion, the first portion being thicker than the second portion;
a base region of the first conductivity type provided on the insulating layer, the base region having a higher impurity concentration than the first portion of the active region, the base region being in contact with the first portion of the active region and the insulating layer;
a drain region of a second conductivity type provided on the insulating layer, the drain region being in contact with the second portion of the active region and the insulating layer, the drain region being spaced from the base region;
a source region of the second conductivity type provided on a surface of the base region;
a gate insulating layer provided on the source region, the base region, the active region and the drain region; and
a gate electrode provided on the gate insulating layer.
2. A MOSFET of claim 1, wherein the gate insulating layer has a first part provided on the source region and a second part provided on the drain region, and the second part of the gate insulating layer is thicker than the first part of the gate insulating layer.
3. A MOSFET of claim 1, wherein the gate insulating layer extends to further in a direction from the source region to the drain region than the gate electrode.
4. A MOSFET of claim 1, further comprising, a contact region being in contact with the drain region and having a higher impurity concentration than the drain region.
5. A MOSFET of claim 4, wherein the gate insulating layer extends to a region on the contact region.
6. A MOSFET of claim 4, wherein the gate electrode extends to a region on the contact region.
7. A MOSFET of claim 5, wherein the gate electrode extends to a region on the contact region.
8. A MOSFET of claim 7, wherein the gate insulating layer extends to further in a direction from the source region to the drain region than the gate electrode.
9. A MOSFET of claim 1, wherein the gate insulating layer has a substantially uniform thickness.
10. A MOSFET of claim 1, wherein the gate insulating layer extends to a region on the drain region.
11. A MOSFET comprising:
an active region of a first conductivity type provided on an insulating layer, the active region having a first portion, a second portion, the first portion being thicker than the second portion;
a base region of the first conductivity type provided on the insulating layer, the base region having a higher impurity concentration than the first portion of the active region, the base region being in contact with the first portion of the active region and the insulating layer;
a drain region of a second conductivity type provided on the insulating layer, the drain region being in contact with the second portion of the active region and the insulating layer, the drain region being spaced from the base region;
a contact region being in contact with the drain region and having a higher impurity concentration than the drain region, a part of the contact region being thicker than the second portion of the active layer;
a source region of the second conductivity type provided on a surface of the base region;
a gate insulating layer provided on the source region, the base region, the active region and the drain region; and
a gate electrode provided on the gate insulating layer.
12. A MOSFET of claim 11, wherein the gate insulating layer has a first part provided on the source region and a second part provided on the drain region, and the second part of the gate insulating layer is thicker than the first part of the gate insulating layer.
13. A MOSFET of claim 11, wherein the gate insulating layer extends to further in a direction from the source region to the drain region than the gate electrode.
14. A MOSFET of claim 11, wherein the gate insulating layer extends to a region on the contact region.
15. A MOSFET of claim 11, wherein the gate electrode extends to a region on the contact region.
16. A MOSFET of claim 14, wherein the gate electrode extends to a region on the contact region.
17. A MOSFET of claim 16, wherein the gate insulating layer extends to further in a direction from the source region to the drain region than the gate electrode.
18. A MOSFET of claim 11, wherein the gate insulating layer has a substantially uniform thickness.
19. A MOSFET of claim 11, wherein the gate insulating layer extends to a region on the drain region.
20. A MOSFET of claim 1, further comprising: a transitional portion provided in the active region between the first portion and the second portion, the transitional portion being thinner than the first portion and thicker than the second portion.