Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Junction field effect transistor
Patent
1996-05-23
1998-07-28
Tran, Minh-Loan
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Junction field effect transistor
257258, 257462, 257136, H01L 2980
Patent
active
057866090
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention proposes a semiconductor structure having both detector and amplifier properties. Such structures are known from earlier patent applications and also from prior art literature. They are suitable for application as independent detectors, as integrated read-out structures of other semiconductor detectors such as drift chambers, drift diodes or CCDs, and particularly as fundamental elements of image cell detectors.
BACKGROUND OF THE INVENTION
In all of these known applications, read-out is performed by comparing the current flow of the unipolar transistor, with and without signal charge which is collected in a potential minimum (negative charge maximum) underneath the transistor channel, i.e., the "internal gate". The system is reset (quenching of the signal charge) either by application of a voltage pulse (positive for stored electrons) at a reset electrode or by a continuous "overflow" of the almost filled potential reservoir.
One problem in the application of this detector principle occurs in arrays using a plurality of these detector amplifier structures. This is the case, for example, with image cell detectors. There, the individual transistors are intended to operate on the lowest static current possible so as to reduce the energy consumption. With threshold voltage variations occurring in the individual transistors in general, even though the transistors are operated on the same voltages, it is not possible to reduce the power consumption of the system in its entirety to an optional minimum. Apart therefrom, different static currents may result in different slopes and hence also different signal gains as well as "offsets".
It is therefore the object of the present invention to operate the detector amplifier structure in the charge collection state near the threshold so that the power consumption in this state will be very low. It is intended that this state establishes itself automatically, substantially independently of the applied voltage or the threshold voltage of the transistor, respectively.
SUMMARY OF THE INVENTION
In accordance with the present invention, this problem is solved by the provision that the source of the transistor is connected to an external source via a capacitance element rather than directly. The mode of operation will be explained with reference to a p-channel DEPFET structure. However, other structures are also contemplated. The source is connected to the capacitor whose second electrode is connected to a fixed potential V.sub.K (e.g. ground potential). The capacitance is integrated into the structure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan and cross-section view of an embodiment according to the present invention;
FIG. 2 is a top plan and cross-section view of another embodiment according to the present invention;
FIG. 3 is a top plan and cross-section view of yet another embodiment according to the present invention;
FIG. 4A is a graph illustrating nodes connected by contacts to selection lines extending in different directions in correspondence with an equivalent circuit diagram and FIG. 4B illustrates an image cell detector formed of basic image cells;
FIG. 5 is a top plan and cross-section view of still yet another embodiment according to the present invention; and
FIG. 6 is a top plan and four cross-sectional views thereof of another embodiment according to the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
One example of the integration according to the invention is shown in FIG. 1, which represents a closed (annular) transistor structure in a substantially completely depleted semiconductor body with n-type doping, in both a cross-sectional and a plan view. The gate (G) and the source (S) can therefore be seen on both sides of the centrally disposed drain (D); a small reset electrode (L) is provided on the right side in the source. The return contact (R) serves to deplete the semiconductor body of charge carriers and to form a potential barrier underneath the upper major face of the stru
Ehwald Karl-Ernst
Kemmer Josef
Lutz Gerhard
Richter Rainer
Max-Planck-Gesellschaft zur Foerderung der Wissenschaflen e.V.
Tran Minh-Loan
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