IT202100004058A1 - GRAPHENE-BASED PERSONAL DOSIMETER - Google Patents

Description

DESCRIPTION

Technical field

The solution disclosed in the present document relates to a dosimeter, ie a detector device used to determine exposure to ionizing radiation, in particular an electronic graphene dosimeter. The solution exposed here? particularly suitable for making a portable dosimeter, for personal use (to determine individual exposure to such ionizing radiation), with low energy consumption.

State of the art

Various environments frequented by living beings, in particular by people, can be exposed to various sources of ionizing radiation of the type, degree and intensity? different. Radiation may be detected in some environments due to the presence of radioactive materials, radiation leaks during the operation of equipment with radiation-producing operations or byproducts, previous nuclear events, or otherwise. Can radiation vary in intensity? and they can take various forms, such as X-rays, gamma rays, neutrons, heavy ions or others. Some radiation sources may emit low levels of radiation continuously, while other sources may emit higher levels of radiation. sporadically but at levels pi? elevated.

To living beings, especially people, can You may find yourself in environments where dangerous levels of radiation may exist. For example, nuclear plant workers may be exposed to radiation if a barrier leak occurs in a chamber containing a radioactive material. Rescue workers and personnel handling hazardous materials may be exposed to radiation when working in emergency situations, such as in the event of malfunctions or component failures in a nuclear power plant. Airport security personnel can be exposed to radiation from the scanning equipment used for routine security checks. Even astronauts can experience radiation during activities? extravehicular in space, generated by solar flares, solar wind of the sun, cosmic rays or other.

Radiation detection in various environments ? fundamental why? those exposed to excessive doses of radiation can be seriously injured or even killed.

because people are generally unable to detect the presence of (a dangerously high level of) radiation using their senses, those working in an environment where they may be at risk of radiation exposure may rely on techniques and/or radiation detection devices.

Solid-state electronic dosimeters are known which use, as a radiation-sensitive element, components normally used for storing data in solid-state electronic memory devices. Known examples of such solid-state electronic dosimeters use, as elements sensitive to ionizing radiation, Flash memories with memory cells comprising floating-gate MOS transistors (?Floating-Gate MOSFET?) or MOS transistors with charge trapping elements (? Charge-Trap MOSFET?).

In relatively recent times, graphene-based non-volatile memory devices have been proposed, such as described in Juqing Liu et al., ?Fabrication of Flexible, All-Reduced Graphene Oxide Non-Volatile Memory Devices?, in Advanced Materials 2013, 25, 233?238.

Presentation of the proposed solution

The solution proposed in this document concerns a graphene-based electronic dosimeter with low energy consumption, particularly suitable for use as a portable, personal dosimeter.

In a first aspect, the solution proposed here refers to a dosimeter comprising a component sensitive to radiation, and a communication interface configured to allow data communication between the dosimeter and an external data processing system.

The radiation sensitive component comprises an rGO-SiC memory comprising a plurality of of memory cells, and the dosimeter includes a?unit? controller configured to control the rGO-SiC memory.

The rGO-SiC memory? a multilevel memory, in which each memory cell of said plurality? of memory cells? designed to memorize a sequence of two or more? bit, between a plurality? of sequences of two or more? storable bits, associated with a respective threshold voltage of the memory cell, for each sequence of storable bits the respective threshold voltage being variable between the memory cells to define a corresponding distribution of predefined threshold voltages.

At least a subset of memory cells of said plurality? of memory cells of multilevel rGO-SiC memory ? programmable to memorize a predefined bit sequence selected among said plurality? of storable bit sequence, associated with a corresponding predefined threshold voltage distribution.

The unit control ? configured to check the memory in a first mode? reading apt to determine the bit sequences stored in the memory cells on the basis of at least two predefined reading reference voltages of a plurality? of predefined reading reference voltages that depend on the predefined threshold voltage distributions.

The unit control ? also configured to control the rGO-SiC memory in a second modality? reading able to determine a state, conductive or non-conductive, of the memory cells of said plurality? of memory cells in response to the application of a predefined reading reference voltage selected among said plurality? of predefined reading reference voltages.

The unit control ? also configured to make a plurality? of read operations of said at least one subset of memory cells in said second modality? reading, each reading operation of said plurality? of read operations being carried out at a respective operative read voltage having a value in the vicinity of said selected predefined read reference voltage.

On the basis of this plurality? of read operations of said at least one subset of memory cells, a current threshold voltage distribution is determined relative to the at least one subset of memory cells.

Through the communication interface, the dosimeter outputs an indication of the current threshold voltage distribution determined in order to allow the external data processing system to determine any radiation exposure of the dosimeter.

The predefined reading reference voltage selected among said plurality? voltage reference reading predefined used in said second mode? of reading can? understand at least one of said plurality? of predefined reading reference voltages intermediate between the predefined threshold voltage distribution corresponding to the predefined bit pattern stored in said at least one subset of memory cells and an adjacent predefined threshold voltage distribution.

The communication interface can? including a wireless, "wireless" communication interface, particularly a BlueTooth communication interface.

Multilevel rGO-SiC memory can be a memory with NAND, NOR or crossbar architecture (i.e. including a selection device for each memory cell), of type 2LC (two levels), 4LC (four levels), 8LC (eight levels) or 16LC (sixteen levels) .

The dosimeter can include a battery to power the unit? controller, multilevel rGO-SiC memory and communication interface.

In a second aspect, the solution proposed here refers to a radiation exposure detection system, comprising:

- a dosimeter in accordance with the first aspect of the solution set forth herein, and - a data processor configured to interact with the dosimeter and programmed to execute a computer program which, when running, ? suitable for:

- controlling the programming, in at least a subset of memory cells of said plurality? of memory cells of the multilevel rGO-SiC memory of the dosimeter, of a predefined sequence of bits selected among said plurality? of sequence of bits that can be stored in the memory cells of the multilevel rGO-SiC memory of the dosimeter, associated with a corresponding distribution of predefined threshold voltages,

- command the dosimeter the execution of said plurality? of read operations of said at least one subset of memory cells in said second modality? reading, each reading operation of said plurality? of read operations being performed at a respective operating read voltage having a value in a neighborhood of said selected predefined read reference voltage, to determine a distribution of current threshold voltages relative to the at least one subset of memory cells,

- receive from the dosimeter an indication of the distribution of voltages with a determined current threshold, e

- determining a possible exposure to radiation by comparison between said predefined threshold voltage distribution and the given current threshold voltage distribution.

In a further aspect thereof, the solution proposed in the present document refers to a method for determining a radiation exposure, comprising:

- providing a multilevel rGO-SiC memory comprising a plurality? of memory cells, in which each memory cell of said plurality? of memory cells? designed to memorize a sequence of two or more? bit, between a plurality? of sequences of two or more? storable bits, associated with a respective threshold voltage of the memory cell, for each sequence of storable bits the respective threshold voltage being variable between the memory cells to define a corresponding distribution of predefined threshold voltages, and in which the memory rGO -Multilevel SiC ? configured to perform readings of the memory cells in a first mode? reading, apt to determine the bit sequences stored in the memory cells on the basis of at least two predefined reading reference voltages of a plurality? of predefined reference reading voltages that depend on the distributions of predefined threshold voltages, and in a second modality? reading, able to determine a state, conductive or non-conductive, of the memory cells of said plurality? of memory cells in response to the application of a predefined reading reference voltage selected among said plurality? of predefined reading reference voltages;

- program at least a subset of memory cells of said plurality? of memory cells of the multilevel rGO-SiC memory for storing a predefined bit sequence selected among said plurality? of storable bit sequence, associated with a corresponding predefined threshold voltage distribution;

- make a plurality? of read operations of said at least one subset of memory cells of the multilevel rGO-SiC memory in said second modality? reading, each reading operation of said plurality? of read operations being carried out at a respective operative read voltage having a value in the vicinity of said selected predefined read reference voltage;

- on the basis of said plurality? of read operations of said at least one subset of memory cells, determining a distribution of current threshold voltages relative to the at least one subset of memory cells, and

- determining a possible exposure to radiation by comparison between said predefined threshold voltage distribution and the given current threshold voltage distribution.

Thanks to the use of a multi-level rGO-SiC memory (Multi-Level Cell or MLC memory, meaning an rGO-SiC memory configured in such a way that its memory cells are capable of store each more than a single bit of information, therefore two or more bits of information for each memory cell) ? It is possible to have a dosimeter that is very sensitive to radiation exposure. At the same time, thanks to the innovative mode? of read access to the multilevel rGO-SiC memory (c.d. ?second modality? of reading?) that ? used as a radiation sensitive element, ? It is possible to drastically reduce the energy consumption of the dosimeter (unlike the energy expenditure that would occur if, for reading access to the multilevel rGO-SiC memory in order to determine any exposure to radiation, the usual access method was adopted ( so-called ?first reading mode?) adopted for reading multilevel rGO-SiC memories when they are used as data storage devices, i.e. the usual reading by memory pages).

Thanks to the solution exposed here ? Is it therefore possible to create a portable dosimeter with low energy consumption and high sensitivity? radiation exposure detection.

Brief description of the figures

The characteristics and advantages of the solution proposed here, so? as further characteristics and advantages, will become evident from reading the following detailed description of its possible embodiments, which are exemplary and non-limiting. For its better intelligibility, the following description should be read referring to the annexed figures, in which:

Fig.1 schematically shows, in terms of the main functional blocks, an exemplary dosimeter in accordance with an embodiment of the solution proposed here;

Fig.2 shows, again schematically but in greater detail, some of the main functional blocks of an rGO-SiC memory device included in the dosimeter of Fig. 1;

Figs. 3A, 3B and 3C show the general principle on which ? based on the operation of a solid state dosimeter using an rGO-SiC memory as a radiation exposure detector;

Fig. 4 shows statistical distributions of the threshold voltages of the memory cells of a multilevel rGO-SiC memory, in particular an 8LC rGO-SiC memory;

Figs. 5A and 5B schematically show the effect of radiation exposure of multilevel rGO-SiC memory, and

Figs. 6 and 7 schematically show the operating principle of the dosimeter of Fig. 1 in accordance with an exemplifying embodiment of the solution proposed here.

Detailed description of exemplary embodiments

In Fig. 1 ? schematically shown, in terms of the main functional blocks, an exemplary dosimeter in accordance with an embodiment of the solution proposed here. The dosimeter, identified as a whole by the reference 100, ? a portable dosimeter, particularly suitable for use as a personal dosimeter. The dosimeter 100 includes an rGO-SiC memory 105.

How will you describe yourself? in more detail below, the rGO-SiC 105 memory? a multilevel memory (by which we mean an rGO-SiC memory configured in such a way that its memory cells are each able to memorize more than a single bit of information, therefore sequences of two or more bits of information for each memory cell), for example a tri-level memory or a four-level memory (8LC memory, configured in such a way that its own memory cells are capable of each storing sequences of three bits of information, or 16LC memory, configured in such a way that its own memory cells are each able to memorize sequences of four bits of information). Does the dosimeter 100 include a unit? of control 110, for example a microcontroller (?C). The dosimeter 100 comprises a communication interface 115, for example of the non-wired type (wireless or ?wireless?), such as for example of the BlueTooth type? configured to allow the dosimeter 100 to communicate with the outside. The dosimeter 100 pu? include additional components, not described here nor? mentioned as deemed irrelevant for the purposes of understanding the solution set out here. Dosimeter 100 includes an internal source of electrical energy 130, such as a battery (e.g., a standard 3.3V nominal button cell battery) arranged to supply electrical energy to the rGO-SiC memory 105, the unit, and controller 110, to the communication interface 115 (and possibly to at least some of the further components of the dosimeter 100 not shown) for their operation.

At least some of the components of the dosimeter 100, for example the memory rGO-SiC 105, the unit? of control 110 and the communication interface 115, and the battery 130 can be mounted on a single chip 120, for example a printed circuit chip (?Printed Circuit Board? or PCB). The components of the dosimeter 100, in particular the plate 120, are preferably boxed in a case 125.

The rGO-SiC memory 105 constitutes the radiation exposure detector or radiation sensitive element, to be understood as the component of the dosimeter 100 in which, following exposure to radiation, changes can occur in certain physical or operational conditions (in this case , variations of the threshold voltages of the memory cells of the rGO-SiC memory 105, as will be explained in detail further on). The unit of control 110 supervises the operation of the dosimeter 100. In particular, the unit? controller 110 interfaces with and manages the rGO-SiC memory 105, accessing it for programming operations (writing and erasing) and reading the data contained in the rGO-SiC memory 105.

By means of the communication interface 115 the dosimeter 100 can? interface with an external data processing equipment 140, for example a personal computer or a terminal of a data processing system, for setting and configuring the dosimeter 100 and for reading the dosimeter 100 (for example to detect any exposure to radiation from the dosimeter).

Fig.2 shows, again schematically but in greater detail, some of the main functional blocks of the rGO-SiC memory 105. The description of the rGO-SiC memory 105 that will follow? provided below ? summary as it is mostly? of concepts known to the technicians of the sector.

The rectangle identified by reference 205 represents a memory cell array (?memory cell array?), with NOR, NAND or crossbar type architecture, with memory cells (not shown) arranged at the intersections between word lines (so-called ?word line?) and bit lines (c.d. ?bit line?). Without going into excessive detail, in itself? known to those skilled in the art, in a memory with NAND architecture there are groups or strings of memory cells of the matrix of memory cells 205; in each string of memory cells the memory cells are connected to each other in series, each memory cell of a given string being associated with a respective word line, and the string of memory cells ? connected to a respective bit line and to a reference electric potential line.

The memory cells of the memory cell matrix 205 of the rGO-SiC memory 105 can for example be or comprise (as schematized in Fig. 3A) an active layer AL made with reduced graphene oxide, sandwiched between two layers of oxide of graphene, of which one, the upper electrode TE, ? strongly reduced (hrGO), while the other, the lower electrode BE, ? slightly reduced (lrGO). The upper electrode TE constitutes the control terminal of the memory cell which is electrically polarized through the control terminal G. The active layer AL? able to trap negative electric charges, the cio? electrons. From an electrical point of view, the structure made up of the upper electrode TE, the active layer AL, the lower electrode BE and the silicon carbide (SiC) substrate, where the S terminals are located (source or ?source?) and D (well or ?drain?), constitutes a real electronic transistor (terminals G ? S - D), wholly equivalent to the well-known MOS transistor (Metal-Oxide-Semiconductor) (hereinafter, we will refer to the electronic transistor defined by the above structure as the ?MOS transistor?). For programming, by subjecting the graphene memory cell to appropriate polarization conditions, ? possible to do s? which charge carriers (typically electrons) ?jump? from the area below the lower electrode BE (formed by silicon carbide or SiC) to the active layer AL and remain trapped there (thanks to the electrical properties of the active layer which is electrically positively charged). The presence of electrons in the active layer determines a modification of the threshold voltage value of the transistor itself: the threshold voltage value ? as much greater as greater ? the quantity? of electrons present in its active layer. By varying the threshold voltage, the electric potential to be applied to the control gate electrode of the transistor varies, necessary to turn it on (that is, to make it conductive).

Returning to Fig.2. the rectangle identified by the reference 210 represents a bit line selector of the rGO-SiC memory 105. The bit line selector 210 ? configured to select the bit lines of the memory matrix 205 (biasing them to the desired electric potential, according to the different operations to be performed on the memory cells). The rectangle identified by the reference 215 represents a word line selector of the rGO-SiC memory 105. The word line selector 215 ? configured to select the bit lines of the memory matrix 205 (biasing them to the desired electric potential, according to the different operations to be performed on the memory cells).

The bit line selector 210 and the word line selector 215 operate under the control of a control logic, represented by the rectangle identified by the reference 220. The control logic 220 receives addressing logic signals 225 from the outside (hereinafter, for brevity?, ?addresses?), which, suitably decoded, allow the addressing (i.e., the selection), through the bit line selector 210 and the word line selector 215, of the desired bit line and word line. The control logic 220 also receives, again from the outside, command logic signals 230 which, suitably decoded, allow the control logic 220 to make the rGO-SiC memory 105 perform the desired operations, such as programming (writing) operations of data into the memory cells of the memory array 205 and reading data from the memory cells stored in the memory cells of the memory array 205.

The rectangle identified by the reference 230 represents a data register, in which the data read from the memory cells of the matrix 205 are temporarily stored (during read accesses to the rGO-SiC memory 105) or to be stored (programmed, written) in the cells memory of the matrix 205 (during write or programming accesses to the rGO-SiC memory 105). In particular, the data register 230 comprises reading circuitry (so-called ?sense amplifier?) of the memory cells to determine the content of the memory cells accessed from time to time.

The data read from the memory cells, or to be programmed (written) in the memory cells (such data are represented in the figure by the double arrow identified by the reference 235), are communicated outside the rGO-SiC memory 105, or received by the? outside of the rGO-SiC memory 105, through input/output buffers represented by the rectangle 240, which interface with the data register 230. In particular, the data to be written in the memory array 205 are supplied to the rGO-SiC memory 105 by the? unit? of control 110, and the data read by the memory array 205 are supplied by the rGO-SiC memory 105 to the unit? control 110.

The rGO-SiC memory 105 comprises a reading reference voltage generator, represented by the rectangle identified by the reference 245, which, under the control of the control logic 220, generates and supplies the word line selector 215 with the appropriate electrical voltages for the execution of the different reading operations of the memory cells, as we will discuss? in more detail below.

Figs. 3A and 3B show the general principle on which ? based on the functioning of a graphene dosimeter. In particular, for mere explanatory purposes, in Figs. 3A and 3B is considered the example of a two-level rGO-SiC memory? 2LC memory ? That ? an rGO-SiC memory configured such that its memory cells are each capable of storing only a single bit (?1? or ?0?) of information. Starting with Fig. 3A, the values of the threshold voltages VTH of the memory cells of the rGO-SiC memory are meant to be represented on a horizontal axis. The distribution ?bell? (Gaussian) 305 represents the statistical distribution of the values of the threshold voltages of a plurality? of memory cells containing the data of logical value ?1? (cells ?deleted? or ?erased?). The bell-shaped (Gaussian) distribution 310 represents the statistical distribution of the values of the threshold voltages of a plurality of memory cells containing the datum of logical value ?0?. To the left of the bell distribution 305 ? shown the symbol of a MOS transistor formed by upper electrode TE, lower electrode BE and active layer AL, in whose active layer there are no electrons (or are there ?few? electrons), a condition which corresponds to a memory cell containing the data of logical value? bits - ?1?); the letters G, S and D respectively identify the control gate electrode, the source electrode and the drain electrode of the MOS transistor. The existence of a statistical distribution (describable by means of a Gaussian curve) of the threshold voltages of the memory cells containing the datum of logical value ?1? derives mainly from the fact that during the manufacturing phase the physical parameters which determine the threshold voltage of the various MOS transistors of the memory cell array 205 vary slightly from memory cell to memory cell as a result of the inevitable manufacturing process tolerances (as well as by the fact that the number of the "few" electrons present in the AL layer is variable). To the left of the bell distribution 310 ? shown the symbol of a MOS transistor in whose active layer AL there are electrons (?many? electrons, significantly more? than the ?few? electrons that can be present in the active layers AL of the MOS transistors containing the logical value data ?1? ), condition which corresponds to a memory cell containing the logical value ? bits - ?0?; the electrons are schematized by small black circles). The existence of a statistical distribution (describable by means of a Gaussian curve) of the threshold voltages of the memory cells containing the datum of logical value ?0?, as well as from the previously mentioned tolerances of the manufacturing process, also derives from the fact that, in phase of programming or writing of the memory cells, the quantity? of electrons that ?jumps? in the active layer AL of the MOS transistors varies from memory cell to memory cell (as a consequence of the small variations of the physical parameters of the MOS transistors induced by the tolerances of the manufacturing process, by the tolerances in the bit line and word line bias voltages, and by various other parameters).

The REFs reference identifies a reading reference voltage value that can? be used (generated by the reading reference voltage generator 245 and supplied to the word line selector 215) during the read access phase to the rGO-SiC memory 105 to discriminate the state of the memory cells, ie? to say to determine if the memory cells contain the datum of logical value ?1? or the data of logical value ?0?. In the figure, the voltage value identified by the reference REFs ? represented as equidistant from the median value of the distribution 305 of the threshold voltage values of the cells containing the logical value datum ?1? and from the median value of the distribution 310 of the threshold voltages of the memory cells containing the logic value datum ?0?, but nothing prevents the value of the reading reference voltage REFs from being slightly lower or higher than that shown in the figure: There? what does it matter, for the purpose of determining the data contained in the memory cell, ? that the reading reference voltage value REFs is located between the two bell-shaped distributions 305 and 310. The memory cells which have a threshold voltage value lower than the reading reference voltage value REFs are read as containing the data of logical value or bit ?1? (ie? as not programmed or erased), while the memory cells which present a threshold voltage value higher than the value of the reading reference voltage REFs are read as containing the logic value datum or bit ?0? (that is, as programmed or written).

Fig. 3B schematizes what? which occurs when the rGO-SiC memory is exposed to radiation 315. At least some of the memory cells which contained the data of logic value ?0?, whose threshold voltage values were represented by the statistical distribution 310, lose at least part of the electrons which were in their active layers AL, as a consequence of the fact that the particles of the radiation 315, if of sufficient energy, are capable, by interacting with the electrons, of extracting them from the active layer AL. By losing at least part of the electrons that were in the active layers AL of the memory cells containing the datum of logic value ?0?, the statistical distribution (bell) of the threshold voltage values of these memory cells is modified, in particular by widening and coming to present a tail on the left pi? extended towards lower values of the threshold voltages, as schematized by the distribution identified by reference 310?.

If the? intensity? of the radiation 315 to which the rGO-SiC memory is exposed? high enough, pu? happen that the left tail of the statistical distribution 310? exceeds the value of the reference reading voltage REFs: in this case, in the subsequent reading of the memory cells of the rGO-SiC memory (with the reference reading voltage REFs), at least some of its memory cells which had initially been programmed (written) to contain the data of logical value ?0? will be read as memory cells containing the datum of logical value ?1?, and from a comparison between the previous situation and the one following the exposure to radiation 315 (which originates ?reading errors?, as memory cells that expected to contain data with a logical value ?0?, instead they are read as containing data with a logical value ?1?) sar? possible to determine that the memory rGO-SiC ? been exposed to radiation.

In a 2LC memory like the one to which you ? with reference in Figs. 3A and 3B the memory cells (e.g. the MOS transistors with active layer AL), the programming circuitry of the memory cells, the internal voltages applied to the memory cells for their programming (writing) and erasing are designed such that the distance between the statistical distribution 305 of the threshold values of the memory cells containing the logical value data ?1? and the statistical distribution 310 of the values of the threshold voltages of the memory cells containing the datum of logic value ?0? ? usually what? high that, even after exposure to radiation 315, the left tail of the modified statistical distribution 310? can? do not exceed the value of the REFs reading reference voltage. Under these conditions, the exposure of the rGO-SiC memory to the radiation 315 would not be detected by a subsequent reading of the memory with the reference reading voltage REFs (because even those memory cells which, following exposure to the radiation 315 , have lost some of the electrons that were present in their active layer AL would continue to have a threshold voltage higher than the reading reference voltage REFs and, consequently, no reading errors would be highlighted, since all the memory cells that expected to contain data with a logical value ?0? would still be read as containing data with a logical value ?0?).

A possibility? to overcome this problem it would consist in carrying out various read accesses to the rGO-SiC memory (after exposing it to the radiation 315), by varying from time to time the value of the reference reading voltage REFs used for the discrimination of the memory cells containing the data of logical value ?1? from those containing the data of logical value ?0?. For example, the value of the reference reading voltage REFs used to read the memory cells could be increased, starting from the value REFs shown in Fig.3A, step-by-step by an amount discrete, making a plurality? of consecutive readings of the memory cells and counting at each step (and therefore at each reading) the number of cells that return the logical value data ?0?, as schematized in Fig.3C, where the value of the reference voltage for reading is gradually increased from an initial value REFs0 to a final value REFsn. This would reconstruct the modified statistical distribution 310?.

Isn't such a methodology? however problem-free.

Since, as explained above, in a memory 2LC the distance between the statistical distribution 305 of the threshold values of the memory cells containing the logical value datum ?1? and the statistical distribution 310 of the values of the threshold voltages of the memory cells containing the datum of logic value ?0? ? usually relatively high, to ensure that in the readings of the rGO-SiC memory to detect any exposure thereof to radiation 315 the left-hand tail of the modified statistical distribution is reached (with the reading reference voltage REFs gradually increased 310? it is necessary to provide, at each step, an increase in the value of the reference voltage of reading REFs rather high, which compromises the sensitivity? of radiation exposure detection. On the contrary, with relatively small increments at each step of the REFs reading reference voltage, in order to maintain an acceptable sensitivity? of the detection, the number of consecutive readings to be performed could become excessively high, with negative effects on the response time of the dosimeter and on its energy consumption (due to the high number of read accesses to be performed, each of which involves a waste of energy not negligible) ? the counterpart of having relatively small increments of the reference reading voltage, to maintain acceptable levels of sensitivity, and a not exaggerated number of consecutive readings would be the risk of not reaching, with the increased reference reading voltage REFs, the left tail of the modified statistical distribution 310?.

So although, how is it? seen, in principle, a memory rGO-SiC 2LC can? be used as a radiation exposure sensitive element in a radiation exposure detector, for example in a dosimeter, the relatively large distance between the average levels (or, equivalently, between the statistical distributions) of the memory cell threshold voltages programmed (conventionally, corresponding to the logic value ?0? of the information bit stored in them) and not programmed (or erased, conventionally corresponding to the logic value ?1? of the information bit stored in them) make rGO-SiC 2LC memories little sensitive as radiation exposure detectors, and dosimeters using rGO-SiC 2LC memories would suffer from similar problems.

As known to those skilled in the art, in addition to two-level memories or 2LCs, there are multi-level memories (Multi-Level Cell memories or MLCs), which are rGO-SiC memories configured in such a way that their memory cells are able to memorize each sequences of pi? of a single bit of information, then sequences of two or more? bits per memory cell. Examples of multilevel memories are the 4LC memories, configured in such a way that their memory cells are able to memorize sequences of two bits of information (therefore four possible combinations or logic values ?11?, ?10?, ?01? and ? 00?), the memories 8LC (or TLC), configured in such a way that their memory cells are able to store each sequence of three bits of information (therefore eight possible combinations or logical values ?111?, ?110?, ?, ?000?), and the memories 16LC (or QLC), configured in such a way that their memory cells are able to each memorize sequences of four bits of information (therefore sixteen possible combinations or logical values ?1111?, ?1110?, ?, ?0000?). Although sometimes MLC memory refers to memories configured so that their memory cells are capable of storing two bits of information, in this document multilevel memory or MLC is meant refer to any memory configured so that its memory cells are able to store sequences of two or even more? bit of information, thus also including TLC memories and QLC memories in the generic denomination of multilevel memory or MLC.

Multilevel memories or MLCs (i.e., the memory cells, the programming circuitry of the memory cells, the internal voltages applied to the memory cells for their programming and erasing) are designed in such a way that the statistical distributions of the voltage values threshold values of the memory cells containing the different possible combinations of values of the information bits (sequences of bits) stored are much less spaced from each other than are the two statistical distributions 305 and 310 of threshold voltage values in the memories 2LC discussed previously. In Fig.4 ? schematized example of an rGO-SiC TLC memory; on a horizontal axis the values of the threshold voltages VTH of the memory cells of the rGO-SiC TLC memory are meant to be represented. The eight ?bells? 405 ? 440 represent the eight statistical distributions (Gaussian) of the threshold voltage values of the memory cells associated with the eight possible configurations of values of the three bits of information stored in the memory cells: conventionally, bell 405 ? associated the combination of logical values ?111?, to the bell 410 ? associated the combination of logical values ?011?, to the bell 415 ? associated the combination of logical values ?001?, to the bell 420 ? associated the combination of logical values ?000?, to the bell 425 ? associated the combination of logical values ?010?, to the bell 430 ? associated the combination of logical values ?110?, to the bell 435 ? associated with the combination of logical values ?100? and to the bell 440 ? associated with the combination of logical values ?101?. The least significant bit of the three bits of information stored in the memory cells corresponds to the so-called ?lower memory page? (?lower page?), the bit pi? of the three bits of information stored in the memory cells corresponds to the c.d. ?upper memory page? (?upper page?) and the middle bit corresponds to the c.d. ?middle memory page? (?middle page?). The references REFA, REFB, REFC, REFD, REFE, REFF and REFG represent the (seven) predefined read reference voltages used for reading the data contained in the memory cells (to determine the bit values of the bit streams stored in the memory cells).

In the rGO-SiC 8LC memories the reading of the stored data takes place by memory pages. ? It is possible to access the memory to read the contents of a lower memory page, or of a middle memory page, or of an upper memory page. Reading the contents of the lower memory page involves determining the logical value of the least significant bit of the combinations of three bits stored in the memory cells; reading the contents of the middle memory page involves determining the logical value of the middle bit of the combinations of three bits stored in the memory cells; does the reading of the contents of the upper memory page involve the determination of the logical value of the pi bit? significance of the combinations of three bits stored in the memory cells. The determination of the logic value of the least significant bit (that is of the lower memory page) involves the execution of two memory cell reading operations, using for the comparison the predefined reading reference voltages REFA and REFE: if from the reading of a generic memory cell it results that its threshold voltage VTH ? lower than the predefined reading reference voltage REFA or greater than the predefined reading reference voltage REFE, is it determined that the logic value of the least significant bit (ie? of the lower page) ? ?1?, otherwise the logical value of the least significant bit (that is? of the lower page) ? ?0?. The determination of the logical value of the middle bit (i.e. of the middle memory page) involves the execution of three memory cell reading operations, using the predefined reading reference voltages REFB, REFD and REFF for comparison: if from the reading of a generic memory cell it results that its threshold voltage VTH ? lower than the predefined reading reference voltage REFB or ? between the predefined reading reference voltages REFD and REFF it is determined that the logical value of the middle bit (ie? of the middle page) ? ?1?, otherwise the logical value of the middle bit (that is? of the middle page) ? ?0?. The determination of the logical value of the pi bit? (i.e. of the upper memory page) provides for the execution of two memory cell reading operations, using for the comparison the predefined reading reference voltages REFC and REFG: if from reading a generic memory cell it results that its threshold voltage VTH ? lower than the predefined reading reference voltage REFC or greater than the predefined reading reference voltage REFG, it is determined that the logic value of the pi bit? significant (ie? of the upper page) ? ?1?, otherwise the logical value of the bit pi? significant (ie? the upper page) ? ?0?.

The rGO-SiC 8LC memories are configured to receive reading commands from the lower memory page, the middle memory page or the upper memory page and to autonomously carry out the memory cell reading operations using the appropriate reference voltages read modes REFA, REFB, REFC, REFD, REFE, REFF and REFG needed to return the content (logical bit values) of the desired memory pages.

In rGO-SiC 8LC memories, in order to determine which of the eight different statistical distributions 405 ? 440 does the threshold voltage of a given memory cell belong? It is necessary to perform various memory cell reading operations. First determine the logical value of the least significant bit (lower memory page), then determine the logical value of the middle bit (middle memory page) and finally determine the logical value of the pi? significant (upper memory page), for a total of seven read operations, using different predefined read reference voltages in each read operation.

As in the case of the 2LC memory discussed above, even in an MLC memory, for example the 8LC memory of the example considered here, when the rGO-SiC memory is exposed to radiation can? occur (as a function of the intensity of the radiation itself) that at least some of the memory cells in which active layers AL were present electrons lose at least some of these electrons, with consequent modification of their threshold voltage values. At least some of the eight statistical distributions 405 ? 440 will change slightly in shape, in particular by widening and coming to present tails on the left more? extended towards lower values of the threshold voltages VTH, as schematized by way of example in Figs. 5A and 5B in which only the two ?bells? 420 and 425 before (Fig. 5A) and after (Fig. 5B) the exposure of the 8LC rGO-SiC memory to radiation: following the exposure to radiation, the shape of the ?bell? 425 changes, assuming the shape of the ?bell? 425? which has a tail on the left pi? extended (a similar change could be made to the ?bell? 420, as well as the bells 410, 415, 430, 435 and 440).

By comparing the memory cell threshold voltages with the predefined reading reference voltage REFD and checking for memory cell read errors (vs. the condition prior to exposure to radiation) it would in principle be possible to determine the ?exposure of rGO-SiC 8LC memory to radiation and the? entity? of the radiation to which the memory ? been exposed.

The relative proximity of the threshold voltage distributions of the memory cells of an MLC memory (such as the eight ?bells? 405 ?440 of the TLC rGO-SiC memory shown by way of example) makes a multilevel rGO-SiC memory a radiation exposure sensitive compared to the 2LC memory considered initially, thus solving the problems highlighted with respect to the latter.

However, the use of a multi-level rGO-SiC memory (e.g. 8LC or 16LC) as a radiation sensitive element introduces significant complexities. in the reconstruction of the distributions of the threshold voltage values of the memory cells, necessary to be able to determine the? entity? of the radiation which the memory ? been exposed. If, as previously discussed, for a 2LC memory ? it is sufficient to vary the value of the (single) reading reference voltage REFs (for example, by successive steps, as schematized in Fig.3C) to (roughly) reconstruct the tail of the modified statistical distribution 310?, for an 8LC rGO-SiC memory it is not enough to vary the value of a predefined reading reference voltage to reconstruct the statistical distribution of the threshold voltage values of the memory cells. Referring to the example shown in Figure 5B, suppose we want to reconstruct the tail of the modified statistical distribution 425? by varying the value of the predefined reading reference voltage REFD. Using an rGO-SiC 8LC memory designed and built for pure data storage applications, ? necessary ?read? the contents of the middle memory page, an operation which, as described above, involves performing three readings of the memory cells, setting the default values of the default reading reference voltages REFB and REFF and then choosing a value for the default reading reference voltage REFD. Suppose that reading of the middle memory page of a generic memory cell returns the logical value ?1? of the middle bit of the combinations of values of the three bits stored in the memory cells: the threshold voltage of the memory cell could belong to the ?bell? 425, or at the ?bell? 430, or again at the ?bell? 410 or even the ?bell? 405 (which represents the statistical distribution of the threshold voltages of the erased memory cells). The reading of the contents of the middle memory page (operation which, as explained, involves three readings of the memory cells) is not possible? therefore sufficient to be able to establish exactly which statistical distribution the threshold voltage of the memory cell in question belongs to. In order to resolve the uncertainty and be able to determine which statistical distribution of the threshold voltages does the threshold voltage of the memory cell in question belong to? it is also necessary to read the remaining two memory pages, lower and upper (operations which, as explained, each involve two readings of the memory cells). Therefore 3 2 2 = 7 reading operations of the memory cells are necessary to be able to determine to which statistical distribution the threshold voltage of the memory cell in question belongs. Similar considerations also apply to each of the other seven statistical distributions of the eight statistical distributions 405 ? 440.

Having to perform such a number of memory cell read operations, as well as an impact on the complexity? computational, implies a substantial expenditure of energy that ? unsustainable if you want to use an rGO-SiC MLC memory to build a battery-powered personal dosimeter that transmits data via, for example, Bluetooth? (or other contactless method).

To overcome this problem, while wanting to benefit from the greater sensitivity? of radiation exposure detection offered by the multilevel rGO-SiC memories (compared to the 2LC rGO-SiC memories), the solution proposed here envisages the use of an rGO-SiC memory configured in such a way that the memory cells are able to memorize each pi? of a single bit of information, as in multilevel rGO-SiC memories (eg in 8LC or 16LC memories), therefore programmable so that their threshold voltages can assume values falling within one of a plurality? of (more than two) statistical distributions, such as the eight statistical distributions or ?bells? 405 ? 440 of the rGO-SiC memory 8LC shown in Fig.4, and at the same time configured in such a way that (unlike what is foreseen in multilevel memories for pure data storage applications) it is operable to perform a ?single level? (?single level read?), as occurs in traditional 2LC memories, by selecting a predefined reading reference voltage among those foreseen for reading the contents of the memory pages, and with the possibility? to vary the value of the predefined reading reference voltage used as a comparison for verifying the state, conductive or non-conductive, of the memory cells in a neighborhood of said selected predefined reading reference voltage, in order to reconstruct the shape of the distribution statistics of the threshold voltage values of the memory cells after a possible exposure to radiation.

In other words, the solution proposed here provides for the use of a known type of multilevel rGO-SiC memory, configured to be able to program its own memory cells in any one of a plurality of memory cells. of (more? than two) programming states, each programming state corresponding to a respective sequence of two or more? bit, and which therefore does not necessarily provide for the execution of the various readings of the memory cells necessary for determining the content of the various memory pages, instead executing a so-called ?single-level reading?, cio? a reading with only one, at choice, among the various predefined reading reference voltages for the normal reading ?by pages?, with the possibility? varying the value of the read reference voltage around said selected predefined read reference voltage in order to reconstruct the shape of the statistical distribution of the threshold voltage values of the memory cells. The existing technology of the multilevel rGO-SiC memories is exploited for the programming of the memory cells, but for the reading a single read is performed as if the multilevel rGO-SiC memory were a 2LC memory, ?spending? the energy budget gender of a 2LC memory and not of a multilevel memory, eg 8LC or 16LC.

Thanks to the solution proposed here ? It is possible to achieve significant energy savings compared to conventional multilevel rGO-SiC memories.

For example, in a conventional 8LC rGO-SiC memory, the ETLC energy expended in a read operation to determine which of the eight 405 statistical distributions ? 440 belongs the threshold voltage of a memory cell ? essentially equal to:

ETLC = VDD*IREAD*(TR_MIDDLE TR_LOWER TR_UPPER)

where VDD indicates the supply voltage of the rGO-SiC memory, IREAD ? the average current absorbed by the memory during a read operation, TR_MIDDLE ? the temporal duration of the reading operation of the middle memory page (which, as previously discussed, provides for the execution of three readings of the memory cells, with the reference voltages REFB, REFD and REFF), TR_LOWER ? the temporal duration of the reading operation of the lower memory page (which, as previously discussed, provides for the execution of two readings of the memory cells, with the reference voltages REFA and REFE) and TR_UPPER ? the time duration of the reading operation of the upper memory page (which, as previously discussed, provides for the execution of three readings of the memory cells, with the reference voltages REFC and REFG).

With the solution proposed here, the ESLR energy spent in a generic reading operation of the contents of the memory cells ? essentially equal to:

where TR_SLR ? the time duration of the read operation performed, as in the rGO-SiC 2LC memories, with a single read reference voltage (for example the read reference voltage REFSLR shown in Fig. 6). The average IREAD current absorbed by the memory during a read operation? (at least in first approximation) independent of the reading method, as confirmed by laboratory measurements on rGO-SiC 8LC memories (or, in general, MLC) and rGO-SiC 2LC memories.

Energy saving? therefore equal to:

In the last generation rGO-SiC 8LC memories the time TR_MIDDLE ? of about 80 ns while the TR_LOWER and TR_UPPER times are about 60 ns each. The time duration TR_SLR of a normal read operation of an rGO-SiC 2LC memory? of about 35 ns. It follows that:

that is? the single level reading involves an energy consumption of about 1/6 the energy consumption required by the conventional reading of an rGO-SiC 8LC memory. To this energy saving must then be added the lower energy consumption of the unit? of control 110 which must remain in operating conditions for a shorter time (TR_SLR instead? TR_MIDDLE + TR_LOWER + TR_UPPER) than what would be necessary if a conventional MLC rGO-SiC memory were used.

The use of an rGO-SiC 16LC memory instead of an rGO-SiC 8LC memory, always operable with single-level reading, results not only in a further increase in sensitivity? (thanks to the fact that in this case the statistical distributions of the threshold voltage values of the memory cells are sixteen and even closer together than the eight statistical distributions of the rGO-SiC 8LC memories), in an even more? significant energy saving compared to the conventional reading of a 16LC rGO-SiC memory. In fact, if in the conventional 8LC rGO-SiC memory the memory pages to be read to determine to which statistical distribution of the threshold voltage values the threshold voltage of a generic memory cell belongs would be three, in a 16LC memory the memory pages to read would be four. In last generation rGO-SiC 16LC memories, the total time required for reading the four memory pages? of about 650 ns, so the ESLR / EQLC ratio? equal to about 1/20.

In accordance with an embodiment of the solution proposed here, as schematized in Fig. 2, the rGO-SiC memory 105 ? a multilevel rGO-SiC memory, which, like conventional multilevel rGO-SiC memories, is configured to be able to program its own memory cells (of the memory matrix 205) in a plurality? of (more than two) different threshold voltage levels, for example eight levels like 8LC memories or sixteen levels like 16LC memories. Unlike conventional multilevel rGO-SiC memories, the 105 rGO-SiC memory? configured to be able to perform, at the request of the unit? control 110, single level readings, as in rGO-SiC 2LC memories. To this end, the control logic 220 of the MLC rGO-SiC memory 105 ? configured to support reception, from the unit? of control 110, of a command which, interpreted by the control logic 220, makes s? that the latter triggers the execution of a reading operation of the single level type of the memory cells (instead of a conventional memory page reading), in which the memory cells are accessed by polarizing their upper electrodes TE with a single preselected reading reference voltage and the current conducted by the memory cells is detected. The single-level reading command can? be a command received as one of the command logic signals 230, although in Fig. 2 that command is graphically represented as a separate SLR command. The SLR command ? supplied to the rGO-SiC MLC 105 memory from the unit? of control 110 of the dosimeter 100. The unit? control 110 pu? include, in the SLR command, an indication of the reading reference voltage value that the MLC 105 rGO-SiC memory will have to? use in the execution of the single level reading operation. For example, with reference to Fig. 6, the unit? control 110 of the dosimeter 100 pu? send to the rGO-SiC memory MLC 105 a single level reading SLR command in which ? contained an indication of the reading reference voltage value REFSLR that the control logic 220 will have to? command (to the reference voltage generator 245, which will supply it to the word line selector 215) to use for reading the memory cells of the matrix 205. In the example shown in Fig. 6, the reference voltage value of REFSLR read to be used in single level read operation ? a value suitable for discriminating whether the memory cells have threshold voltage values belonging to the statistical distribution 420 or to the statistical distribution 425. The choice of the reading reference voltage value REFSLR to be used for single-level reading of the memory cells ? determined by the choice made in the initial configuration phase of the dosimeter 100, in which the cells of the memory matrix 205 of the rGO-SiC memory 105 (or a preselected subset thereof) are programmed in a predefined state of the eight possible states possible for the memory 8LC, for example in the state ?010? (bringing their threshold voltage to assume values falling within the ?bell? 425). During the verification of the possible exposure of the dosimeter 100 to radiations, the unit? controller 110 of the dosimeter 100 accesses the MLC rGO-SiC memory 105 to determine the state of those memory cells initially programmed in state ?010?. By comparing the initially programmed state of conduction of the memory cells and that read following a possible exposure to radiation, ? possible to determine if the dosimeter 100 ? been exposed to radiation (if there has been exposure, the reading of the memory cells originally programmed in the predefined state will give rise to reading errors, which are indicative of the exposure of the dosimeter 100 to radiation).

In particular, according to an embodiment of the solution proposed here, in order to reconstruct the shape of the statistical distribution of the threshold voltages of the memory cells of the matrix 205 (or of the selected subset of memory cells), the unit? of control 110 of the dosimeter 100 ? configured to carry out repeated single-level read accesses to the rGO-SiC MLC 105 memory, varying from time to time the value of the reading reference voltage REFSLR to be used for single-level reading of the memory cells in the vicinity of the reference voltage selected default reading reference, for example the default reading reference voltage REFD (if the chosen threshold voltage distribution for radiation exposure monitoring is the 425 distribution). For example, start with a single-level read using a reference voltage value REFSLR- lower than the default read reference voltage REFD, and count the number of memory cells that return a logical ?1? (memory cells which therefore have a threshold voltage value lower than the value of the reference voltage REFSLR-). Is the reading operation repeated with a reference voltage value increased by a quantity? discrete?REFSLR with respect to the starting reference voltage value REFSLR- and the number of cells returning the logical value ?1? is counted again, then making the difference between the number counted and the number counted previously. This operation is repeated a predetermined number of times, each time increasing the reference voltage value by an amount? discrete ?REFSLR with respect to the reference voltage value used in the previous iteration, until reaching a higher reference voltage value REFSLR+. Thus, you perform a plurality? of successive reads using read reference voltages in the vicinity REFSLR- -REFSLR+ of the predefined read reference voltage REFD. At the end of the procedure, is a reconstruction of the shape of the 425 statistical distribution obtained? (possibly modified with respect to the statistical distribution 425 as a result of the exposure of the dosimeter 100 to radiation).

Does what just described in relation to the example of the statistical distribution 425 of the threshold voltages of the memory cells of the rGO-SiC memory 8LC apply to any of the statistical distributions 410? 440. As the statistical distribution of threshold voltages chosen to detect any exposure to radiation varies, the values of the predefined reading reference voltages with which the single level readings must be performed vary.

During the initial configuration of the dosimeter, the cells of the matrix 205 of the rGO-SiC memory MLC 105 can be programmed in various ways, so to be stored in the rGO-SiC MLC 105 memory a desired predefined pattern. In the phase of detecting the possible exposure of the dosimeter to radiation, single level readings of different subsets of memory cells of the memory matrix 205 will be carried out using the appropriate reading reference voltages. Thanks to the solution exposed here, ? Is it possible to make a highly sensitive portable dosimeter? of detection of? exposure to radiation, with very low power consumption, which can? be powered by a common battery, such as a nominal 3.3 V button cell battery. Returning to Fig. 1, once the dosimeter 100 ? been initialized, for example by the personal computer 125, it is provided to a person whose radiation exposure it is desired to monitor. The initialization of the dosimeter 100 involves among other things the writing in the rGO-SiC memory 105 of a predetermined initial configuration of data for (at least a subset of the) cells of the rGO-SiC memory. In this phase, the communication interface 115, the unit? controller 110 and rGO-SiC memory 105 are kept powered through battery 130.

In the field, the 130 battery only needs to provide energy to maintain the unit? controller 110 of the dosimeter and the communication interface 115 in a condition of ?sleep alert?, which involves a very low consumption. When it is desired to read the dosimeter 100, for example by means of the personal computer 125, to determine whether the person who has worn it ? been exposed to radiation and the entity? of the radiations themselves, the dosimeter 100 pu? be approached to the personal computer 125 that will send? a ?wake up? (?wake up?) to communication interface 125. The ?wake up? will awaken? the unit? of control 110, which will feed? the memory rGO-SiC 105 and light? the contents thereof, by sending the read data to the personal computer 125. A suitable application running on the personal computer 125 will receive? the data read from the rGO-SiC memory 105 and, by comparison with the initial predetermined configuration which ? was initially written in the dosimeter 100 in the initialization phase, sar? able to determine the entity? of the radiation exposure of the dosimeter 100, and therefore of the person who wore it.

The hierarchical architecture of conventional rGO-SiC memories provides, in addition to the subdivision into memory cells and memory pages, the presence at the upper level of multiple? ?plans? memory pages each comprising a certain number of memory pages. Different memory plans can be accessed in parallel by executing different operations on each of them simultaneously (for example, it is possible to program a memory plan and, at the same time, read another memory plan). The parallel reading of two (or more?) memory plans (a memory page in each plan) allows an energy saving because? two (or more?) memory pages are read simultaneously. The solution exposed here? also applicable to the simultaneous reading, at a single reading reference voltage level, of two or more? memory plans of rGO-SiC memory.

It should also be underlined that, although in the foregoing reference has always been made to modifications in the distributions of the threshold voltages of the memory cells which involve ?enlargements? of the same distributions towards lower values of the threshold voltages as a consequence of the exposure to radiations (determined by the removal of electrons from the active layers AL responsible for the trapping of charge of the memory cells), some radiations to which the dosimeter can? be exposed could cause changes in the distributions of the threshold voltages which also (or only) involve ?widening? of the distributions of the threshold voltages towards values more? elevated (that is, "enlargements" to the right in the diagrams shown in the figures), a consequence of the fact that exposure to radiation could determine the passage in the active layers AL of additional electrons with respect to those already? present there. Do the principles of the solution described here apply equally well to such a situation and the methodology described ? capable of reconstructing also such modifications in the form of threshold voltage distributions. For example, considering again the distribution 425 of Fig.6, a widening towards the right of the same distribution can be identified by choosing, as the predefined reading reference voltage, the reading reference voltage REFE and varying it in its range of values.

The solution that is the subject of this document? been described in detail with reference to possible embodiments thereof, which are exemplary and non-limiting. Variations of the embodiments described as well as other embodiments are possible and within the reach of the person skilled in the art without departing from the scope of the claims which follow. For example, nothing prevents that, in alternative embodiments, the communication interface 115 of the dosimeter 100 to allow the dosimeter 100 to communicate with the outside, which in the example described is? of the non-wired type (?wireless?), can be implemented, in addition or alternatively, of the wired type, for example as a USB interface.

It is also underlined that although in the foregoing reference has been made, by way of example, to a multilevel rGO-SiC memory, i.e. a memory consisting of a thin layer of reduced graphene oxide (rGO) deposited on silicon carbide (SiC), the solution set out here also applies to multilevel memories based on graphene, reduced or non-reduced, deposited on silicon (Si) or silicon oxide (Si02). Furthermore, the exposed solution can be apply indifferently to memory cells organized with NAND, NOR or crossbar architecture.

TRANSLATION OF THE WORDS IN THE FIGURES

Plate Board

Erased

Programmed Programmed

Electron Electron

Programmed after radiation Programmed after radiation

Lower Page Lower page

Middle page Middle page

Upper page Upper page

Single Level Read Single Level Read

Claims (7)

1. Dosimeter including: - a radiation sensitive component, the radiation sensitive component comprising an rGO-SiC memory (105) comprising a plurality of? of memory cells, - a?unit? controller (110) configured to control the rGO-SiC memory, - a communication interface (115) configured to allow data communication between the dosimeter and an external data processing system (125), wherein: - the rGO-SiC memory? a multilevel memory, in which each memory cell of said plurality? of memory cells? designed to memorize a sequence of two or more? bit, between a plurality? of sequences of two or more? storable bits, associated with a respective threshold voltage of the memory cell, for each sequence of storable bits the respective threshold voltage being variable between the memory cells to define a corresponding distribution of predefined threshold voltages (405 - 440), - at least a subset of memory cells of said plurality? of memory cells? programmable to memorize a predefined bit sequence selected among said plurality? of storable bit sequence, associated with a corresponding predefined threshold voltage distribution (425), e - the unit? control (110) ? configured to check the memory in a first mode? reading apt to determine the bit sequences stored in the memory cells on the basis of at least two predefined reading reference voltages of a plurality? of predefined reading reference voltages (REFA-REFG) which depend on the predefined threshold voltage distributions, in which: the unit? control (110) ? configured to control the rGO-SiC memory in a second modality? reading able to determine a state, conductive or non-conductive, of the memory cells of said plurality? of memory cells in response to the application of a predefined reading reference voltage (REFSLR) selected among said plurality? of predefined reading reference voltages, the unit? control being also configured for: make a plurality? of read operations of said at least one subset of memory cells in said second modality? reading, each reading operation of said plurality? of read operations being carried out at a respective operative read voltage (REFSLR- - REFSLR+) having a value in the vicinity of said selected predefined read reference voltage; on the basis of this plurality? of read operations of said at least one subset of memory cells, determine a distribution of current threshold voltages (425?) relative to the at least one subset of memory cells, and output from the dosimeter, through the communication interface (115), an indication of the distribution of current threshold voltages determined in order to allow the external data processing system (125) to determine a possible radiation exposure. 2. The dosimeter according to claim 1, wherein the predefined reading reference voltage is selected among said plurality of voltage reference reading predefined used in said second mode? of reading includes at least one of said plurality? of predefined read reference voltages (REFSRL) intermediate between the predefined threshold voltage distribution corresponding to the predefined bit sequence (425) stored in said at least one subset of memory cells and an adjacent predefined threshold voltage distribution. The dosimeter according to claim 1 or 2, wherein said communication interface (115) comprises a wireless communication interface, particularly a BlueTooth communication interface. 4. Dosimeter according to any one of the preceding claims, wherein the rGO-SiC memory? a memory consisting of a thin layer of reduced graphene oxide (rGO) deposited on silicon carbide (SiC), particularly an 8LC or 16LC type rGO-SiC memory. 5. Dosimeter according to any one of the preceding claims, comprising a battery (130) for powering the unit? controller, multilevel rGO-SiC memory and communication interface. 6. Radiation exposure detection system including: - a dosimeter (100) according to any one of claims 1 to 5, e - a data processor (125) configured to interact with the dosimeter and programmed to execute a computer program which, when running, ? suitable for: - controlling the programming, in at least a subset of memory cells of said plurality? of memory cells of the multilevel rGO-SiC memory (105) of the dosimeter, of a predefined sequence of bits selected among said plurality? of sequence of bits storable in the memory cells of the multilevel rGO-SiC memory (105) of the dosimeter, associated with a corresponding distribution of predefined threshold voltages (425), - command the dosimeter (100) the execution of said plurality? of read operations of said at least one subset of memory cells in said second modality? reading, each reading operation of said plurality? of read operations being performed at a respective operative read voltage (REFSLR- - REFSLR+) having a value in a neighborhood of said selected predefined read reference voltage, to determine a distribution of current threshold voltages (425?) relative to the? at least a subset of memory cells - receiving from the dosimeter (100) an indication of the determined current threshold voltage distribution (425?), and - determining a possible exposure to radiation by comparison between said predefined threshold voltage distribution (425) and the determined current threshold voltage distribution (425?). 7. A method for determining radiation exposure comprising: - providing a multilevel rGO-SiC memory (105) comprising a plurality? of memory cells, in which each memory cell of said plurality? of memory cells? designed to memorize a sequence of two or more? bit, between a plurality? of sequences of two or more? storable bits, associated with a respective threshold voltage of the memory cell, for each sequence of storable bits the respective threshold voltage being variable between the memory cells to define a corresponding distribution of predefined threshold voltages (405 - 440), and in which the multilevel rGO-SiC memory ? configured to perform readings of the memory cells in a first mode? reading, apt to determine the bit sequences stored in the memory cells on the basis of at least two predefined reading reference voltages of a plurality? of predefined reading reference voltages (REFA-REFG) which depend on the distributions of predefined threshold voltages, and in a second modality? reading, able to determine a state, conductive or non-conductive, of the memory cells of said plurality? of memory cells in response to the application of a predefined reading reference voltage (REFSLR) selected among said plurality? of predefined reading reference voltages; - program at least a subset of memory cells of said plurality? of memory cells of the multilevel rGO-SiC memory for storing a predefined bit sequence selected among said plurality? of storable bit sequence, associated with a corresponding predefined threshold voltage distribution (425); - make a plurality? of read operations of said at least one subset of memory cells of the multilevel rGO-SiC memory in said second modality? reading, each reading operation of said plurality? of read operations being carried out at a respective operative read voltage (REFSLR- -REFSLR+) having a value in the vicinity of said selected predefined read reference voltage; - on the basis of said plurality? of read operations of said at least one subset of memory cells, determining a distribution of current threshold voltages (425?) relative to the at least one subset of memory cells, and - determining any radiation exposure by comparison between said distribution of predefined threshold voltages (425) and the determined current threshold voltage distribution (425?).