A monolithically integrated ISFET sensor array and interface circuit are described. A new high-density, low-power source-drain follower was developed for the sensor array. ISFETs were formed by depositing Au/Ti extended-gate electrodes on standard MOSFETs, then thin silicon nitride layers using catalytic chemical vapor deposition and/or SU-8 protective layers were formed on the extended-gate electrodes. Applications for the array include: (1) pH detection by statistical distribution observing time and space fluctuations; (2) DNA detection using thiol-modified or silane-coupled oligonucleotides; (3) bio-image sensing by converting photons to electrons using Photosystem I of Thermosynechococcus elongatus, and sensing the converted electric charges by ISFETs.

In this paper, we present a self-powered bio-sensing system with the capability of proximity inductive-coupling communication for supply sensing and temperature monitoring. The proposed bio-sensing system includes a biofuel cell as a power source and a sensing frontend that is associated with the CMOS integrated supply-sensing sensor. The sensor consists of a digital-based gate leakage timer, a supply-insensitive time-domain temperature sensor, and a current-driven inductive-coupling transmitter and achieves low-voltage operation. The timer converts the output voltage from a biofuel cell to frequency. The temperature sensor provides a pulse width modulation (PWM) output that is not dependent on the supply voltage, and the associated inductive-coupling transmitter enables proximity communication. A test chip was fabricated in 65 nm CMOS technology and consumed 53 μW with a supply voltage of 190 mV. The low-voltage-friendly design satisfied the performance targets of each integrated sensor without any trimming. The chips allowed us to successfully demonstrate proximity communication with an asynchronous receiver, and the measurement results show the potential for self-powered operation using biofuel cells. The analysis and experimental verification of the system confirmed their robustness.

We propose a compact model of ballistic gate-all-around metal-oxide-semiconductor field-effect transistors. In this model, the potential distribution in the wire cross section is approximated by a quadratic function. This model potential has one unknown parameter, which determines the shape of the potential. The Schrödinger equation in the wire cross section can be approximately solved using the model potential, and the electron energy levels are derived analytically. The unknown parameter is determined by numerically solving a coupled equation for charge densities derived from electrostatics and quantum statistics. We calculate the device properties using the obtained unknown parameter. A Schrödinger-Poisson solver that simulates electron states in the wire cross section is used. The results obtained using it reveal that our model exhibits good agreement for both the lowest and excited energy levels. We estimate the ballistic current using the calculated energy levels and the Landauer formula, which shows good agreement with results simulated using the nonequilibrium Green's function formalism.