Apparatuses and methods using current-starved ring oscillator biased by floating gate transistors with a variety of applications including as a power-free radiation detector or silicon age determination or odometer system

Abstract

Apparatuses and methods using current-starved ring oscillator biased by floating gate transistors with a variety of applications including as a power-free radiation detector or silicon age determination or odometer system.

Claims

1. A method of detecting radiation comprising: providing a first device from a plurality of devices in a common wafer lot comprising a radiation detector system comprising a current-starved ring oscillator biased by floating gate transistors irradiating the first device and generating measurement data comprising measured floating gate current starved (FGCS) frequency vs TID data of first device to create a lookup table containing the measurement data; and reading FGCS frequency in other said plurality of devices in the common wafer lot and using the lookup table to convert frequency degradation to accumulated total ionizing dose.

2. A method of detecting radiation comprising: providing a first device from a plurality of devices in a common wafer lot comprising a radiation detector system comprising a current-starved ring oscillator biased by floating gate transistors, wherein the plurality of devices further comprises a second device provided as a reference device that comprises a reference circuit; irradiating the first device and generating measurement data comprising measured floating gate current starved (FGCS) frequency vs TID data of the first device to create a lookup table containing the measurement data; and reading FGCS frequency in at least the second device and using the lookup table to convert frequency degradation to accumulated total ionizing dose, wherein the FGCS to reference frequency comparison is calculated using a beat frequency circuit or by using two on-chip counters' clocked with a same reference clock, wherein the comparison to help cancel out environmental effects like temperature and system effects such as supply voltage variations.

3. A method of detecting aging of an electrical circuit that includes a silicon structure comprising: providing an electrical circuit age detection system comprising a current-starved ring oscillator biased by floating gate transistors; disposing the electrical circuit age detection system in an environment; and determining age of at least one section of an electrical circuit that includes a silicon structure using the electrical circuit age detection system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The detailed description of the drawings particularly refers to the accompanying figures in which:

(2) FIGS. 1A-1B show an embodiment that replaces each current limiting transistors in a current starved oscillator with a FG cell;

(3) FIG. 2 shows an embodiment that includes one or more common FG biasing current limiting transistors;

(4) FIG. 3 shows an exemplary method for using an embodiment of the invention as a radiation detector using a raw frequency value look up table calibrated from radiation data obtained by a representative wafer lot sample device;

(5) FIG. 4 shows an exemplar method for using an embodiment of the invention as a radiation detector using a frequency ratio look up table calibrated from radiation data obtained by a representative wafer lot sample device; and

(6) FIG. 5 shows an exemplary schematic representation of a circuit to compare the frequencies of an exemplary FGCS oscillator and a reference CS oscillator in accordance with one or more embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) The embodiments of the invention described herein are not intended to be exhaustive or to limit the invention to precise forms disclosed. Rather, the embodiments selected for description have been chosen to enable one skilled in the art to practice the invention.

(8) Various novel architectures and methods are provided that integrate CMOS based FG cells to bias the current limiting transistors in a current starved oscillator. Exemplary FG gate cells are provided that have a variable amount of leakage depending upon an oxide thicknesses of transistors sharing a common gate terminal. A number of transistors sharing the common gate terminal can also increase the leakage. Charge on the FG can be removed over time through leakage or by exposing the FG cell to ionizing radiation. Either case of charge removal from the FG, can be used to reduce source to gate voltage (VsG) of an exemplary transistor and thus increase the resistance which will lead to a decrease in measured oscillator frequency.

(9) Referring to FIGS. 1A-1B, an embodiment is shown that replaces each of the current limiting transistors in a current starved oscillator with a FG cell. This implementation allows for lower leakage on each individual FG.

(10) Referring to FIG. 2, another embodiment is shown that uses a single FG to bias each of the current limiting transistors in a current starved oscillator with a FG cell. This implementation increases leakage of the FG cell.

(11) Referring to FIG. 3, an exemplary method is shown for using an embodiment of the invention as a radiation detector. In particular, an exemplary method for using an embodiment of the invention as a radiation detector is shown using a raw frequency value look up table calibrated from radiation data obtained by a representative wafer lot sample device. In this exemplary method, one device from a common wafer lot, Device A, is irradiated to obtain a look up table containing the floating gate current starved (FGCS) frequency vs TID data of the wafer lot. Subsequent devices from the wafer lot, such as device B, can then use the remaining section of the flow to read the FGCS frequency and use the lookup table to convert frequency degradation to accumulated TID.

(12) Referring to FIG. 4, another exemplary method is shown for using an embodiment of the invention as a radiation detector. In particular, FIG. 4 shows an exemplary embodiment used in an exemplary radiation detector method using a frequency ratio look up table calibrated from radiation data obtained by a representative wafer lot sample device. Similar to FIG. 3, this method uses a reference device from the wafer lot as a comparison, but includes a reference circuit in the comparison to help cancel out environmental effects like temperature and system effects such as supply voltage variations. The FGCS to reference frequency comparison can be calculated using a beat frequency circuit or by using two on-chip counters' clocked with a same reference clock. An exemplary generic schematic level representation of the comparison circuit is shown in FIG. 2.

(13) FIG. 5 shows a schematic representation of a circuit to compare the frequencies of the FGCS oscillator and a reference CS oscillator.

(14) Exemplary methods shown in FIGS. 3-4 can be adjusted to measure frequency changes to due charge loss on the FG caused by aging as well in order to create a silicon odometer to determine approximate circuit age for supply chain tracking purposes. A rate of time-based charge leakage can be adjusted to increase by using thinner gate oxides or by increasing the number of transistors sharing the same FG as shown in FIG. 2.

(15) Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the spirit and scope of the invention as described and defined in the following claims.