Integrated Buffer Circuit for Rear-Side Substrate Thinning Detection
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Solution Overview
Problem
Existing methods for detecting substrate thinning in integrated circuits from the rear face are often unreliable and can be tampered with by attackers, especially when temperature variations cause false readings and spatial requirements are not met.
Innovation Solution
A non-inverting buffer comprising complementary MOS transistors and a control circuit that generates distinct signals for substrate thinning detection, utilizing a buried semiconductor layer and vertical/horizontal transistors to ensure reliable detection with reduced spatial requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing detection means are used to detect substrate thinning, then detection capability is provided, but the device has low integration level and disrupts operation of nearby components
Solution Approach 1:
The detection device is merged with the integrated circuit substrate itself. The detection circuit is formed within the same substrate using the same semiconductor layers and structures, eliminating the need for separate detection components. This integration approach resolves the contradiction by providing reliable detection capability while maintaining high integration level and avoiding disruption to nearby components.
Solution Approach 2:
The semiconductor substrate serves multiple functions: it acts as both the functional component carrier for the integrated circuit and as the detection element for thinning detection. The same substrate that carries the circuit components also contains the detection circuit that monitors its own thinning, achieving multi-functionality that resolves the contradiction between detection reliability and device integration.
2Measurement precision
If resistance-based detection is used to detect substrate thinning, then detection is provided, but temperature variations cause false readings
Solution Approach 1:
The detection mechanism transitions from using resistance (which is temperature-dependent) to using current measurements. By measuring the current through the semiconductor substrate and comparing it to reference currents, the system achieves temperature-independent thinning detection. This parameter change from resistance to current resolves the contradiction by eliminating temperature-induced false readings while maintaining detection precision.
Solution Approach 2:
Reference currents are introduced as intermediary elements that serve as temperature-stable comparison standards. The detection circuit measures the ratio between the substrate current and reference currents, using the reference currents as mediators that cancel out temperature effects. This intermediary approach resolves the contradiction by providing a temperature-compensated measurement method.
3Reliability
If existing detection devices are used, then substrate thinning can be detected, but attackers can modify the device to falsify detection results
Solution Approach 1:
The detection circuit is built into the substrate during the original manufacturing process, before the substrate can be accessed or modified by attackers. The detection structures are formed simultaneously with the functional circuit components in the same fabrication steps. This preliminary action of integrating detection during manufacturing resolves the contradiction by making the detection device immune to later tampering while maintaining its detection capability.
Solution Approach 2:
The detection circuit is nested within the functional integrated circuit itself. The detection structures are embedded among the functional components, sharing the same substrate and fabrication processes. This nesting approach resolves the contradiction by making the detection device inseparable from the functional circuit, preventing attackers from modifying one without affecting the other, while maintaining compact integration.
4Area of stationary object
If compact detection device is implemented, then spatial requirements are reduced, but detection reliability must be maintained
Solution Approach 1:
The detection circuit is merged with the functional integrated circuit components, sharing the same substrate, fabrication processes, and physical space. The detection structures are formed using the same semiconductor layers and materials as the functional devices. This merging resolves the contradiction by achieving compact spatial requirements through integration while maintaining detection reliability through the use of the same high-quality fabrication processes.
Data Source
AI summary
A semiconductor substrate includes a buried semiconductor layer and semiconductor wells. A device for detecting a possible thinning of the semiconductor substrate via the rear face thereof is formed on and in the semiconductor wells. The device is a non-inverting buffer including an input terminal and an output terminal, the device being powered between a supply terminal and a reference terminal where the buried semiconductor layer provides the supply terminal. A control circuit delivers an input signal in a first state to the input terminal and outputs a control signal indicating a detection of a thinning of the substrate if a signal generated at the output terminal in response to the input signal is in a second state different from the first state.