Dynamic Reconfigurable Security Cells Based on Emerging Devices Integrable in FDSOI Technology

While a number of measures have been proposed to protect the integrity of COS hardware, there are some inherent limitations from classical CMOS methods. Those already existing security methods, like logic locking can be improved with emerging technologies such as Reconfigurable Field Effect Transistors (RFETs). RFETs are a special type of doping-free, Schottky transistors which can work as a PFET or NFET as a function of biasing across its gates. In the present study we developed standard cell layouts for dynamic reconfigurable security cells based on three-independent-gated RFETs (TIG-RFETs). They layouts are compatible to an industrial 22nm FDSOI technology, feature the minimum pitch of the baseline technology, and obey all design rules necessary for co-integration. The designs enable a fair area comparison for RFET based digital application for the first time. Based on the sizing constraints from the layouts, a TCAD model of such a TIG-RFET is developed in Sentaurus TCAD to illustrate two biasing schemes for the application of TIGRFETs in this platform: reconfigurability with individual body-bias per transistor and reconfigurability at globally fixed body-bias. Due to the different operation options three variants of reconfigurable 2-XOR-XNOR and 2-NAND-NOR logic cells exhibiting different level of utility are designed. While the smallest dynamic 2-NAND-NOR gate needs roughly double the area of a CMOS 2-NAND gate from the reference library, the smallest 2-XOR-XNOR gate is only 20% larger than a CMOS 2-XOR. To quantify the area overhead for hardware security applications we calculated the number of logic locking gates that can be added per area overhead for a given circuit, here the ISCAS-85 C6288 benchmark circuit, as an example. Dynamic replacement based logic locking with TIG-RFETs shows to allow up to double the number of keys compared to classical CMOS logic locking per area overhead. Therefore, this work allows a realistic view on the application of RFETs in hardware security and its co-integrability along with some design constraints from an industrial PDK.