Embedded Shield for FPGA Memory Cell Protection

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Solution Overview

Problem

Programmable integrated circuits, particularly Field Programmable Gate Arrays (FPGAs), face vulnerabilities in protecting encryption keys stored in battery-backed random access memory (BBRAM) when powered down, as they can be susceptible to thermal laser stimulation attacks, and there is a risk of physical access to memory cells if the shield is removed.

Innovation Solution

An embedded Faraday cage shield is integrated into the FPGA structure to block electromagnetic radiation and prevent Seebeck voltage generation, combined with a detector circuit that erases data stored in BBRAM cells if the shield is removed, ensuring secure protection of encryption keys and memory contents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Duration of action of stationary object

If BBRAM cells are used to store encryption keys when powered down, then data retention capability is improved, but vulnerability to thermal laser stimulation attacks increases

Engineering Contradiction:

Improvedata retention capabilityVSAvoidvulnerability to thermal laser stimulation attacks

Core Design Contradiction:

Duration of action of stationary objectVSObject-affected harmful factors

Solution Approach 1:

A shield structure is introduced as an intermediary element between the external environment and the BBRAM cells. The shield acts as a physical barrier that blocks thermal laser radiation from reaching the memory cells, thereby preventing Seebeck voltage generation while allowing the BBRAM to maintain its data retention capability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The shield structure, which may be detected as a foreign object or modification, is actually beneficial as it converts the harmful thermal laser energy into a blocked signal, preventing the Seebeck effect that would otherwise allow attackers to extract encryption keys from the BBRAM cells

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Object-affected harmful factors

If a shield is added to block electromagnetic radiation, then protection against thermal laser attacks is improved, but device complexity increases

Engineering Contradiction:

Improveprotection against thermal laser attacksVSAvoiddevice complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The shield structure is merged with existing FPGA packaging elements or substrate structures, combining the protective function with existing device components rather than adding completely separate protective elements, thereby minimizing the increase in device complexity

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The shield structure serves multiple functions: it blocks thermal laser radiation, provides physical protection to the BBRAM cells, and may serve as part of the overall device packaging or substrate structure, thereby justifying its inclusion despite the added complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Ease of repair

If the shield is removed for physical access, then ease of repair or modification is improved, but security of encryption keys deteriorates

Engineering Contradiction:

Improveease of physical accessVSAvoidsecurity of encryption keys

Core Design Contradiction:

Ease of repairVSReliability

Solution Approach 1:

The detector circuit is configured to detect the absence or removal of the shield structure before an attacker can access the BBRAM cells. When shield removal is detected, the system proactively erases the encryption keys in advance, preventing any potential security breach

Inventive Principle:

Principle #9Preliminary anti-action

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

The solution effectively protects BBRAM cells from physical attacks by blocking electromagnetic radiation and automatically erasing data if the shield is compromised, enhancing the security of encryption keys and user designs in FPGAs, even when the device is powered down.

Implementation Method 1

The shield can act as an embedded Faraday cage and can block electromagnetic radiation from impinging on, and reduce or prevent an induced voltage on, devices

Methodology Applied

Scientific EffectFaraday cage: Faraday Cage

Implementation Method 2

The shield is positioned aligned with the protected region... block electromagnetic radiation from impinging on

Methodology Applied

Scientific EffectElectromagnetic radiation blocking: Absorption (EM radiation)

Implementation Method 3

The detector circuit is coupled to and configured to detect a presence of the shield... configured to detect a resistance of the electrical path

Methodology Applied

Scientific EffectElectrical conductivity detection: Conduction (electrical)

Data Source

PatentUS11508667B1Embedded shield for protection of memory cells

Publication Date: 2022.11.22 XILINX INC

AI summary

Some examples described herein provide for a shield in an integrated circuit (IC) structure for memory protection. In an example, an IC structure includes a semiconductor material, an interconnect structure, and a shield. The semiconductor material has a protected region. Devices are disposed in a first side of the semiconductor material in the protected region. The interconnect structure is disposed on the first side of the semiconductor material. The interconnect structure interconnects the devices in the protected region. The shield is disposed on a second side of the semiconductor material opposite from the first side of the semiconductor material. The shield is positioned aligned with the protected region.