Secure integrated circuit chip with conductive shield

DETAILED DESCRIPTION We claim: 1.
An integrated circuit chip containing a secure area in which secure data is processed and/or stored, comprising a semiconductive layer containing diffusions defining circuit element components; a first conductive layer coupled to the semiconductive layer to interconnect the components to thereby define circuit elements for distributing, storing, processing and/or affecting the processing of secure data; and a second conductive layer overlying the circuit elements to thereby define a secure area in which the circuit elements are shielded from inspection, and coupled to the circuit elements for conducting to the circuit elements a predetermined signal that is essential to an intended function of the circuit elements, whereby removal of the second conductive layer will prevent the predetermined essential signal from being provided to the circuit elements and thereby prevent the intended function.
2.
An integrated circuit chip according to claim 1, wherein the predetermined signal is a power signal.
3.
An integrated circuit chip according to claim 2, wherein the shielded circuit elements include a volatile memory for storing secure data, with the memory being powered by the predetermined power signal.
4.
An integrated circuit chip according to claim 3, wherein each of a plurality of the volatile memories is separately coupled to only that portion of the second conductive layer that overlies such memory for receiving the predetermined power signal from only that overlying portion of the second conductive layer.
5.
An integrated circuit chip according to claim 2, further containing a nonsecure area in which nonsecure data and control signals are processed and/or stored, wherein the shielded circuit elements include logic circuit elements for enabling transfer of nonsecure data and/or control signals between the secure area and the nonsecure area, with the logic circuit elements being powered by the predetermined power signal.
6.
An integrated circuit chip according to claim 5, wherein each of a plurality of the logic circuit elements is separately coupled to only that portion of the second conductive layer that overlies such logic circuit element for receiving the predetermined power signal from only that overlying portion of the second conductive layer