A kind of diode string structure
Technical field
The present invention relates to a kind of diode string structure that is applied to aspects such as analog circuit, electrostatic discharge protective circuit or high speed circuit, particularly a kind of polysilicon diode string structure promptly utilizes polysilicon to do the structure of diode string.
Background technology
The present popular basic structure of using conventional diode as the diode string in the actual design of analog circuit, electrostatic discharge protective circuit and high speed circuit and utilization, this kind diode string structure generally forms on silicon substrate, its structure as shown in Figure 1, wherein: 1, anode, 2, metal multi-crystal silicification thing, 3, P type injection region, 4, N type injection region, 5, N trap injection region, 6, P type silicon substrate, 7, negative electrode; Shown in metal multi-crystal silicification thing 2 be the resistance that is used to reduce contact hole and injection region.As shown in the figure, this kind structure may be implemented on the silicon substrate, and carries out impurity and inject the final diode string that forms.The characteristics of this kind structure are to increase new technology, utilize the trap injection in the CMOS technology can form PN junction with the surperficial injection of N type, the injection of P type.But also there are some shortcomings in the diode structure of above-mentioned routine, as because there is size restrictions the minimum interval between each N trap injection region of this structure, and requires greatly than the size of space between the N type injection region, thereby structural area is bigger; For another example because a reverse parasitic diode is arranged between the silicon substrate of conventional diode structure N trap injection region and P type, when at the anode biasing, because P type silicon substrate is electronegative potential (ground connection), therefore can form bigger leakage current by parasitic triode PNP, influence the operate as normal of circuit; Owing to the parasitic diode that in the diode structure of routine, exists between N trap injection region and the P type silicon substrate, also there is parasitic capacitance effect equally, can has influence on the reaction speed of high speed circuit.
Summary of the invention
The technical problem to be solved in the present invention provides a kind of polysilicon diode string structure, can overcome that conventional diode string structure area is big, leakage current big and have the problem of parasitic capacitance.
For solving the problems of the technologies described above, the present invention proposes a kind of diode string structure, promptly on the field oxide isolator of silicon substrate, form the carrier of polysilicon (Poly) as several diodes, diode is made up of P type injection region and N type injection region, bunchiness is alternately arranged in the P type injection region of adjacent two diodes and N type injection region, and forms connection with burning silication thing (Silicide) between adjacent two diodes.The number of above-mentioned diode is more than or equal to two.Above-mentioned diode string structure can be applicable to radio circuit or uses in the common simulation circuit and electrostatic discharge protective circuit of circuit of diode string of forward.
The present invention since the structure of having utilized polysilicon structure and diode string of the present invention in design on field oxide isolator, can be when realizing the diode string of same number, littler than the diode structure area of routine, leakage current is littler and parasitic capacitance is little.
Description of drawings
Fig. 1 is conventional diode string structure generalized section;
Fig. 2 is a diode string structure generalized section of the present invention;
Fig. 3 is the generalized section of a specific embodiment of the present invention;
Fig. 4 is the schematic equivalent circuit of Fig. 3;
Reference numeral:
1, anode, 2, metal multi-crystal silicification thing, 3, P type injection region, 4, N type injection region, 5, N trap injection region, 6, P type silicon substrate, 7, negative electrode;
8, anode, 9, metal multi-crystal silicification thing, 10, P type injection region, 11, N type injection region, 12, polysilicon, 13, field oxide isolator, 14, silicon substrate, 15, negative electrode;
17, anode, 18, metal multi-crystal silicification thing, 19, P type injection region, 20, N type injection region, 21, polysilicon, 22, field oxide isolator, 23, silicon substrate, 24, negative electrode.
Embodiment
The present invention is further detailed explanation below in conjunction with the drawings and specific embodiments.
Diode string structure of the present invention is to make full use of a kind of polycrystalline silicon material characteristics to make up diode string structure, promptly utilize polysilicon in the CMOS technology as the carrier of diode, injection by the technology of utilization own on it forms different impurity formation PN junctions, and the burning silication thing with technology own forms connection between adjacent two diodes.As shown in Figure 2, be diode string structure generalized section of the present invention, wherein: 8, anode, 9, metal multi-crystal silicification thing, 10, P type injection region, 11, N type injection region, 12, polysilicon, 13, field oxide isolator, 14, silicon substrate, 15, negative electrode.The number of diode of the present invention should be more than or equal to two.
Embodiment:
As shown in Figure 3, generalized section for a specific embodiment of the present invention, three diodes are formed a diode string among this embodiment, wherein: 17, anode, 18, metal multi-crystal silicification thing, 19, P type injection region, 20, N type injection region, 21, polysilicon, 22, field oxide isolator, 23, silicon substrate, 24, negative electrode; Fig. 4 is the schematic equivalent circuit of Fig. 3.In the enforcement, utilize the polysilicon that has now in the CMOS technology as the carrier that illustrates three diodes, form different three PN junctions of impurity formation by utilizing to inject on polysilicon, the burning silication thing with CMOS technology between adjacent two diodes forms connection.
Structure of the present invention can apply to the device reaction speed is had relatively high expectations, in the little radio circuit of ghost effect; Common analog circuit, the circuit that is applied to the diode string of forward in the electrostatic discharge protective circuit also can adopt this polysilicon structure.
Diode string structure of the present invention has following excellent for the diode string structure of routine Point: 1, save area. For the diode structure of routine, the minimum between each N trap injection region Between be separated with size restrictions, and require big than the size of space between the N-type injection region; And it is of the present invention Polysilicon structure does not use the N trap to inject, and therefore when realizing the diode string of same number, utilizes this The invention structure can be dwindled area. 2, leakage current is little. For the diode structure of routine, the N trap is annotated Entering between the silicon substrate of district and P type has an individual reverse parasitic diode, when at the anode biasing, by Be electronegative potential (ground connection) in P type silicon substrate, therefore can form bigger by parasitic triode PNP Leakage current affects the normal operation of circuit; And the structure of diode string of the present invention is because of on insulating barrier And avoided this problem. 3, parasitic capacitance is little. Owing in the diode structure of routine, there is the N trap Also just there is parasitic capacitance effect in parasitic diode between injection region and the P type silicon substrate, also can shadow Ring the reaction speed to high speed circuit, and diode string structure of the present invention has been avoided this problem.
In sum, for the diode string structure of routine, the present invention utilizes polycrystalline silicon material Do diode string structure, it is little to have an area, and electric leakage is few, and ghost effect is little, with the conventional cmos worker Skill is fully compatible, the advantages such as easy realization.