The present inventions relate to electrostatic discharge circuits, and particularly electrostatic discharge circuits using forward biased circular-arc shaped steering diodes.
Electrostatic discharge (ESD) is a well known phenomenon that must be taken into consideration during the design of many different types of circuits, such as processors, application specific integrated circuits, and the like. Essentially, when an ESD event occurs (typically in the form of a rapid pulse of undesired energy), the ESD circuit that is associated with the circuit is used to shunt the undesired energy away from the circuit to protect it.
An example of a known circuit that is used to provide ESD protection is illustrated in
Further, as voltages used in circuits generally have decreased, there has been a need for increasing ESD performance in the industry. However increasing ESD performance is associated with higher capacitance of the ESD device. For high speed signaling, increasing ESD capacitance is not acceptable, since it reduces the signal integrity of the system. Accordingly, there is a need for ESD circuits that can provide greater ESD protection with further reductions in input capacitance.
The present invention advantageously provides a circular-arc shaped structure for forward biased steering diodes used in an ESD circuit, which circular-arc shaped structure forward biases steering diodes effectively prevent concentration of an ESD pulse to one section of the p-n junction within the forward biased steering diode (or, alternatively viewed, evenly distributing stress along the entire p-n junction), thus increasing reliability of the ESD circuit, and also minimizing input capacitance as well as occupying a smaller area. The circular-arc shaped structure thus provides a mechanism to evenly distribute the current flow through the ESD steering diodes, and therefore avoids the disadvantage of a voltage gradient along the steering diode structure.
These and other aspects and features of the present inventions will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, wherein:
a) and 3(b) illustrate top view and cross sectional views (along the lines indicated in
a) and 4(b) are correspondingly size-accurate top views of ESD circuits according to an embodiment and a conventional finger pattern implementation, respectively, that shows relative area savings according to the embodiment.
a)1 and 4(a)2 are a top view and a circuit view of the ESD circuit shown in
a)-5(d) illustrate a two-metal layer ESD circuit with a circular arc-shaped structure according to an embodiment.
a) and 3(b) illustrate top view (which view does show components that are at different levels in order for relationships between these components to be understood) and cross sectional views (along the lines indicated in
These circular-arc shaped structure forward biased steering diodes 32Dn and 34Dp effectively prevent concentration of an ESD pulse to one section of the p-n junction within the forward biased steering diodes 32Dn and 34Dp by evenly distributing stress along their entire p-n junction, thus increasing effectiveness of the ESD circuit, and also minimizing input capacitance.
As shown also by
The circular-arc shaped p-n junction and correspondingly shaped bond pad structures described above provide the most effective distribution of stress along the p-n junction. While the amount of the arc can vary, having an equal distance from any point on the p-n junction to the center of the bonding pad is desirable.
In use, when the circuit 30 shown in
In an ESD event, the current will flow through either one of the steering diodes 32Dn or 34Dp as well as the clamping diode D1, also referred to as a zener diode in the art. The clamping diode D1 will provide an effective clamp to protect the steering diode 34Dp by limiting the peak voltage on both the anode and cathode of the steering diode 34Dp.
As is apparent from
a)-5(d) illustrate a two-metal layer ESD circuit 40 with a circular arc-shaped structure according to an embodiment.
These circular arc shaped structures forward biased steering diodes 42Dn and 44Dp effectively prevent concentration of an ESD pulse to one section of the p-n junction within the forward biased steering diode by evenly distributing stress along the entire p-n junction, thus increasing effectiveness of the ESD circuit, and also minimizing input capacitance.
As shown also by
It is also noted that for the various different embodiments described above, the various semiconductor layers, dopant regions, metal layers, as well as insulation and electrical connections shown in the Figures can be fabricated using conventional semiconductor fabrication techniques, and as such a detailed fabrication description is not provided herein.
Although the present invention has been particularly described with reference to embodiments thereof, it should be readily apparent to those of ordinary skill in the art that various changes, modifications and substitutes are intended within the form and details thereof, without departing from the spirit and scope of the invention. Accordingly, it will be appreciated that in numerous instances some features of the invention will be employed without a corresponding use of other features. Further, those skilled in the art will understand that variations can be made in the number and arrangement of components illustrated in the above figures. It is intended that the scope of the appended claims include such changes and modifications.
This application claims priority to U.S. Provisional Application No. 61/052,629, filed May 12, 2008, entitled “Electrostatic Discharge Circuit Using Forward Biased Circular Shaped Steering Diodes”, the contents of which are expressly incorporated by reference herein.
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Number | Date | Country | |
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61052629 | May 2008 | US |