Circuit alteration detection in integrated circuits

A method comprising:

• receiving a first impedance signal from a first shield line of a plurality of shield lines disposed over an integrated circuit in one or more metal lines;
• receiving a second impedance signal from a second shield line of the plurality of shield lines;
• comparing the first impedance signal to the second impedance signal;
• and
• generating a signal to initiate a countermeasure response when the first impedance signal is different from the second impedance signal by greater than a tolerance value.

A system, comprising:

• a shield in at least one metal layer over an integrated circuit and comprising a plurality of shield lines;
• a detector coupled to the shield to detect a change in impedance characteristics of one or more of the plurality of shield lines of the shield due to physical alteration of the shield, wherein the detector comprises a comparator, wherein the comparator comprises a first input node selectively coupled to the shield and a second input node coupled to the shield;
• a first reference resistor coupled at one end to a first voltage line;
• a second reference resistor coupled at one end to the first voltage line;
• and
• three switches for each shield line, including a first switch that selectively couples one end of a shield line to a voltage supply line;
• a second switch that selectively couples another end of the shield line to the first input node of the comparator and another end of the first reference resistor;
• and a third switch that selectively couples the another end of the shield line to the second input node of the comparator and another end of the second reference resistor.