Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2003-02-20
2004-11-23
Le, Dung A. (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S370000
Reexamination Certificate
active
06822289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to semiconductor devices having transistors such as those called insulated gate type transistors, metal insulator semiconductor (MIS) type field effect transistors and MOS transistors. The present invention specifically relates to a semiconductor device suitable for being mounted on a liquid jet apparatus such as an ink jet apparatus, a DNA chip and an organic transistor and also relates to a liquid jet apparatus using such a semiconductor device. The liquid jet apparatus is used as an output terminal of a copying machine, a facsimile, a word processor, a computer and the like.
2. Related Background Art
An example of a semiconductor device used with a liquid jet apparatus will be described.
A semiconductor device for a liquid jet head has electrothermal conversion elements, switching elements for switching the electrothermal conversion elements, and a circuit for driving the switching elements, all being fabricated on the same substrate.
FIG. 20
is a schematic cross sectional view showing a portion of a liquid jet head having a conventional structure.
Reference numeral
901
represents a semiconductor substrate made of single crystal silicon. Reference numeral
912
represents a p-type well region,
908
represents an n-type drain region having a high impurity concentration,
916
represents an n-type drain region having a low impurity concentration,
907
represents an n-type source region having a high impurity concentration, and
914
represents a gate electrode, these elements constituting a switching element
930
made of a MIS type field effect transistor. Reference numeral
917
represents a silicon oxide layer serving as a heat accumulation layer and an insulating layer,
918
represents a tantalum nitride film serving as a heat generating resistor layer,
919
represents an aluminum alloy layer serving as a wiring layer, and
920
represents a silicon nitride layer serving as a protective layer, these elements constituting a main base
940
for a recording head. An area
950
is a heat generating area, and ink is jetted out of a jet port
960
. A top plate
970
together with the main base
940
defines a liquid path
980
,
Large current is required to drive a large load such as an electrothermal conversion element. If a conventional MIS type field effect transistor
930
is used for driving the electrothermal conversion element, the pn junction between the drain and well region cannot resist a high electric field generated by a reverse bias. Leak current is therefore generated and the breakdown voltage necessary for a switching element is hard to be satisfied. In addition, if an on-resistance of the MIS type field effect transistor used as the switching element is large, current is wastefully used so that current necessary for driving the electrothermal conversion element becomes hard to be obtained.
In order to solve the problem of the breakdown voltage of the switching element, a double diffusion metal oxide semiconductor (DMOS)
20
shown in
FIG. 21
may be used.
In
FIG. 21
, reference numeral
152
represents a main base on which an electrothermal conversion element
141
serving as a load, a DMOS transistor
20
and a MOS transistor (not shown) are integrated. Reference numeral
153
represents a jet port,
154
represents a wiring electrode,
155
represents a liquid path, and
156
represents a top plate.
The structure of the DMOS transistor
20
is different from that of a general MOS transistor. A channel is formed later in the drain so that the drain can be made deep and its impurity concentration can be made low. The problem of the drain breakdown voltage can therefore be solved.
Although the DMOS transistor
20
has the characteristics sufficient for a high breakdown switching element, it is not versatile.
The reason for this will be specifically described with reference to FIG.
22
.
FIG. 22
is a circuit diagram of a circuit which has a load and a switching element and flows current through the load by controlling the operation of the switching element.
With the circuit arrangement shown in
FIG. 22
, if the power supply voltage VDD is set to 5.0 V or 3.3 V, a high level voltage signal output from an AND gate
46
is VDD. This signal is applied to a CMOS circuit
52
such as a CMOS inverter and input to the gate control electrode of the switching element
41
.
An important point is the value of a voltage VHT applied to the CMOS circuit
52
. The voltage VHT determines a voltage to be applied to the gate of the switching element
41
. The value of VHT is required to be designed so that the on-resistance of the switching element
41
becomes lowest. If the on-resistance is made lowest, the size of a MOS transistor constituting the switching element, i.e., the area of an integrated circuit chip occupied by the MOS transistor, can be made smallest.
If this voltage is to be generated in the one chip integration circuit including the circuit shown in
FIG. 22
, it is necessary to change the voltage level from the power supply voltage VH to the voltage VHT in the integration circuit.
A transistor source follower circuit is used as the circuit for changing the voltage level, i.e., as a level shift circuit. The constant voltage VHT may be obtained by using the transistor source follower circuit (refer to Japanese Patent Application Laid-Open No. 10-034898, U.S. Pat. No. 6,302,504).
According to the knowing of the present inventor, no problem occurred if a sufficient drain breakdown voltage of a source follower transistor of the level shift circuit is obtained under the conditions of a highest power supply voltage VH of 30 V, a lowest reference voltage VGNDH of 0 V and a middle reference voltage VHT of 12 V.
However, the source of the source follower transistor was broken down when the highest power supply voltage VH was raised to 33 V, the lowest reference voltage VGNDH was set to 0 V and the middle reference voltage VHT was raised to 15 V, because of the reverse bias voltage of 15 V applied across the pn junction between the source and well regions of the source follower transistor.
Although attention is generally paid to the drain breakdown voltage, according to the knowing of the present inventor, attention is also required to be paid to the source breakdown voltage if the circuit shown in
FIG. 22
is used at high power supply voltages.
An object of the invention is to provide a semiconductor device having a high source breakdown voltage, high performance and high reliability, and a liquid jet apparatus using such a semiconductor device.
Another object of the invention is to provide a semiconductor device capable of stably flowing large current through a load and capable of high integration, and a liquid jet apparatus using such a semiconductor device.
SUMMARY OF THE INVENTION
According to a main aspect of the invention, there is provided a semiconductor device having a switching element for flowing current through a load and a circuit for driving the switching element, respectively formed on a same substrate, wherein: the circuit comprises a source follower transistor for generating a drive voltage to be applied to a control electrode of the switching element; and a source region of the source follower transistor comprises: a first doped region connected to a source electrode; and a second doped region having an impurity concentration lower than an impurity concentration of the first doped region, the second doped region forming a pn junction with a semiconductor region forming a channel.
In the semiconductor device of the invention, it is preferable that the switching element is a DMOS transistor, the DMOS transistor comprising: a low impurity concentration drain region made of semiconductor of a second conductivity type and formed in a principal surface of a semiconductor substrate of a first conductivity type; a semiconductor region of the first conductivity type formed in the low impurity concentration drain region; a gate electrode as the control electrod
Iketa Osamu
Kozuka Hiraku
Morii Takashi
Shimotsusa Mineo
Fitzpatrick ,Cella, Harper & Scinto
Le Dung A.
LandOfFree
Semiconductor device and liquid jet apparatus using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor device and liquid jet apparatus using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor device and liquid jet apparatus using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3333667