ESD Protection of ISFET sensors
First Claim
1. Apparatus for selectively measuring ions in a liquid, comprising:
- (a) a measuring circuit including a chemically sensitive ion sensor in the form of an ion sensitive field effect transistor (ISFET) formed on a silicon substrate;
(b) an electrostatic discharge (ESD) protection circuit integrated onto said substrate; and
(c) interface means, integrated onto said substrate, for providing an interface between said protection circuit and said liquid, characterized in that said interface means provides a contact with said liquid without opening up paths for D.C. leakage currents between the ISFET and said liquid.
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Accused Products
Abstract
Methods, apparatus and chip fabrication techniques are described which provide electrostatic discharge (ESD) protection to ion-sensitive field effect transistor (ISFET) based devices used to selectively measure ions in a liquid. According to one aspect of the invention, an ESD protection circuit, made up of conventional protective elements, is integrated onto the same silicon chip on which the ISFET is formed, along with an interface that is in contact with the liquid being measured and which does not open up paths for D.C. leakage currents between the ISFET and the liquid. According to a preferred embodiment of the invention, a capacitor structure is used as the interface between the protection circuit and the liquid sample. Further aspects of the invention are directed to methods per se for providing ESD protection for ISFET sensors utilizing the interface means (e.g, capacitor structure) referred to hereinabove, and processes for fabricating the novel interface on a silicon wafer.
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Citations
13 Claims
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1. Apparatus for selectively measuring ions in a liquid, comprising:
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(a) a measuring circuit including a chemically sensitive ion sensor in the form of an ion sensitive field effect transistor (ISFET) formed on a silicon substrate; (b) an electrostatic discharge (ESD) protection circuit integrated onto said substrate; and (c) interface means, integrated onto said substrate, for providing an interface between said protection circuit and said liquid, characterized in that said interface means provides a contact with said liquid without opening up paths for D.C. leakage currents between the ISFET and said liquid. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. Apparatus for providing electrostatic discharge (ESD) protection to an ion sensitive field effect transistor (ISFET) based measuring device used to measure ion activity in a liquid, comprising:
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(a) an ESD protection circuit fabricated on a silicon substrate, including; (a1) a first bi-directional zener diode coupled to the source of said ISFET; (a2) a second bi-directional zener diode coupled to the drain of said ISFET; and (a3) a uni-directional zener diode coupled to said substrate; and (b) interface means, integrated onto said substrate together with said ESD protection circuit, for providing an interface between said protection circuit and said liquid without opening up paths for D.C. leakage currents between the ISFET and said liquid. - View Dependent Claims (9)
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10. Apparatus for providing electrostatic discharge (ESD) protection to an ion sensitive field effect transistor (ISFET) based sensor chip used to measure ion activity in a liquid test sample, comprising:
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(a) means for transferring charge, built up in said liquid test sample as a result of an ESD event, to the source, drain and substrate of said ISFET; and (b) interface means, integrated onto said chip together with said means for transferring charge, for providing an interface between said protection circuit and said liquid without opening up paths for D.C. leakage currents between the ISFET and said liquid. - View Dependent Claims (11)
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12. Apparatus for providing electrostatic discharge (ESD) protection to an ion sensitive field effect transistor (ISFET) based sensor chip used to measure ion activity in a liquid test sample, comprising:
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(a) means for building up charge in said test sample during an ESD event; and (b) means for transferring charge built up in said liquid test sample, as a result of said ESD event, to the source, drain and substrate of said ISFET. - View Dependent Claims (13)
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Specification