Floating-Gate Memory Protection via Self-Erasing Capacitive Structure
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Solution Overview
Problem
Conventional methods for protecting data in integrated circuit memories against reverse engineering are ineffective when the integrated circuit is not powered or if its functionality is destroyed, as they require activation or mechanical intervention to detect and prevent data recovery.
Innovation Solution
The implementation of capacitive structures within the integrated circuit, comprising a first electrically-conducting body coupled to the floating gate and a second electrically-conducting body coupled to a ground terminal, which are designed to lose stored data upon contact with an aqueous solution or exposure to a focused ion beam, ensuring data loss without powering the circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional protection methods are used, then data security is maintained when the circuit is powered, but data can be recovered through mechanical machining or FIB when the circuit is not powered
Solution Approach 1:
The patent implements protection structures (conductive bodies coupled to floating gates) during the fabrication process itself, before the circuit is deployed. These structures are pre-configured to automatically discharge floating gate charges upon contact with aqueous solutions or exposure to FIB, ensuring protection is active regardless of circuit power state. This preliminary action eliminates the vulnerability window when the circuit is unpowered.
Solution Approach 2:
The protection mechanism is self-activating and does not require external control or power. When an aqueous solution contacts the circuit or FIB is applied, the conductive bodies automatically create discharge paths for the floating gate charges, causing data loss without requiring any active circuit operation. The system protects itself autonomously based on physical contact conditions.
2Loss of information
If the integrated circuit is machined mechanically or by FIB to access memory cells, then data can be recovered, but the circuit functionality is destroyed
Solution Approach 1:
The patent converts the harmful effects of reverse engineering tools into beneficial protection mechanisms. Aqueous solutions used in mechanical polishing naturally trigger discharge of floating gate charges through the conductive bodies. Similarly, FIB exposure causes charge leakage through the same structures. The very tools attackers use to recover data become the mechanism that destroys the data, turning their harmful action into a protective feature.
Solution Approach 2:
The patent changes the electrical parameters of the floating gate by introducing conductive bodies that alter the charge retention characteristics. Under normal conditions, the floating gate maintains charge for data storage. When exposed to aqueous solutions or FIB, the parameter changes (charge leakage through conductive paths) cause automatic data loss, creating a state-dependent protection mechanism that responds to physical intervention.
3Measurement precision
If probes are placed in contact with memory cells to recover data, then data can be read, but the protection mechanisms are bypassed
Solution Approach 1:
The patent applies protection specifically at the critical location of the floating gate, where data is stored. Conductive bodies are positioned to couple directly with the floating gate, creating localized discharge paths. This local quality approach ensures that any probe or tool attempting to access the floating gate must pass through or near the conductive bodies, which will discharge the charge and destroy the data, making targeted data extraction impossible.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively protects data by ensuring intrinsic loss of information during reverse engineering attempts, regardless of the method used, whether mechanical polishing or focused ion beam machining, without requiring the integrated circuit to be functional.
Implementation Method 1
the dielectric body is configured for electrically coupling the floating gate and the ground terminal so as to modify the charge on the floating gate and to lose the corresponding data if an aqueous solution is brought into contact with the dielectric body
Implementation Method 2
at least one capacitive structure comprising a first electrically-conducting body coupled to the floating gate of the state transistor, a dielectric body, and a second electrically-conducting body coupled to a ground terminal
Data Source
AI summary
An integrated circuit memory includes a state transistor having a floating gate which stores a respective data value. A device for protecting the data stored in the memory includes a capacitive structure having a first electrically-conducting body coupled to the floating gate of the state transistor, a dielectric body, and a second electrically-conducting body coupled to a ground terminal. The dielectric body is configured, if an aqueous solution is brought into contact with the dielectric body, to electrically couple the floating gate and the ground terminal so as to modify the charge on the floating gate and to lose the corresponding data. Otherwise, the dielectric body is configured to electrically isolate the floating gate and the ground terminal.