Patent Publication Number: US-9838389-B2

Title: Integrated circuit, code generating method, and data exchange method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part application of and claims the priority benefit of a prior application Ser. No. 14/038,772, filed on Sep. 27, 2013, now pending.The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND 
     Field of the Invention 
     The invention relates generally to an integrated circuit, a code generating method, and a data exchange method. 
     Description of Related Art 
     Encryption and authentication technologies have been crucially required to make sure the security of the network, as the network has been prevailing since the mid of the last century. Most of these technologies have been designed by assuming that they are used in a server or PC which has powerful computational ability. For example, anti-virus software and random-number generating software need powerful computation to work. In recent years, on the other hand, there have been increasing chances of small equipment which have less computational power can be connected to the network, such as SIM-card, sensors, smart-meters, smart-cards, USB memories, and so on. The network composed of small equipment like these causes the birth of new application service with the usage of cloud-computing, social network, smart-grid, machine-to-machine (M2M) network, and so on. Since an LSI chip is a component of the small equipment, the number of the chips used in the network must be substantially increased. Thus, some new technology is required to be embedded into LSI chips, in order to make sure the security of the network composed of LSI chips each of which has less computational power. As a result, it is anticipated that the device-level module must be demanded for encryption and authentication. It is also noted that the cost of the security module in the chip is a significant factor. 
     Generally, a device level module for security includes a) a circuit to carry out the operation of encryption and authentication, and b) a circuit to save/maintain the confidential information that is necessary to operate encryption and authentication (key-maintenance). 
     It should be noted that the 2 nd  part (key-maintenance) is added to the chip, which increases the cost of the chip. It is also noted that the attacker will possibly attack the key-maintenance. An example of key-maintenance is illustrated in  FIG. 1 . 
     (Physically-Unclonable Function) 
     In recent years, as illustrated in  FIG. 2 , it is expected that the key-maintenance circuit will be replaced by a physically unclonable function (PUF), in which an individual difference of chip is used to identify the chip. For example, the module of PUF will return an output (R) with respect to an input (C) as shown in  FIG. 3 . Another chip will return another output with respect to the same input, as shown in  FIG. 4 . One can identify a chip with the output difference among chips with respect to the same input. In other words, PUF will create the ID as necessary and it is not necessary to store the ID in the memory. 
     (Utilization of PUF) 
     (Authenticity) As long as the output (R) from a chip is different from any other chip, this output can be regarded as an ID number of chip, as shown in  FIG. 4 . 
     (Copy Protect) It is possible to create a common encryption key (Key-A) from the output (R-A) of a chip-A. It is also possible to create a common encryption key (Key-B) from the output (R-B) of a chip-B. As shown in  FIG. 4 , Key-B must be different from Key-A with respect to the same input (C). Once a program is encrypted with Key-A, the program cannot be executed with any other LSI (LSI-B) because Key-B is different from Key-A. 
     (Requirement for PUF)
     a) (Unpredictability) It is impossible or very hard to predict a combination of input (C1) and output (R1) from other combinations of input-output, (C2)-(R2), (C3)-(R3) . . . with regard to a chip. In  FIG. 5 , it is assumed that the combinations of (C1)-(R1), (C2)-(R3) . . . (Cn)-(Rn) are known. In this event, it must be impossible or very hard to predict a combination of (Cn+1)-(Rn+1).   b) (Originality) Any two chips must return different returns (R1 and R2, where R1≠R2) with respect to the same input (C), as shown in  FIG. 4 .   c) (Reproducibility) Noise causes, in general, the output from a device to fluctuate around a mean value (R). The fluctuation (ΔR) must be smaller than the difference between any two outputs (|ΔR|&lt;|R l −R m | for  ∀ l and  ∀ m), as shown in  FIG. 6 .   

     (Merits of PUF)
     a) (Invisible label) The return from PUF can be regarded as an invisible label that is randomly and independently attached to each LSI chip without any additional design. It is useful to distinguish certificated or not, as shown in  FIG. 7 . It is noted that the return from PUF is not necessary to be saved in memory; which means “invisible”.   b) (Copy Protect) An encryption key can be created from the return from PUF. Once a program is encrypted with a key created by PUF in a chip, it cannot be executed with any other chip as long as PUF appropriately operates, as shown in  FIG. 8 .   

     However, nothing herein should be construed as an admission of knowledge in the prior art of any portion of the invention. Furthermore, citation or identification of any document in this application is not an admission that such document is available as prior art to the invention, or that any reference forms a part of the common general knowledge in the art. 
     SUMMARY OF THE DISCLOSURE 
     Accordingly, the invention is directed to integrated circuits and code generating methods capable of physically unclonable identification of a chip. 
     According to an exemplary embodiment, an integrated circuit is provided. The integrated circuit includes at least one first input/output end, at least one current path connected with the first input/output end, at least one control end disposed above the at least one current path and configured to apply a plurality of control end voltages on the at least one current path, and at least one second input/output end connected with the current path. At least one current adjusting element is disposed in at least one of the current paths to adjust an electrical current. In some embodiments, the at least one current adjusting element includes at least one dopant ion, and at least either the width or the thickness of the current path are defined according to the de Broglie length (DBL), and the length of the current path is longer than the width of the current path. In other embodiments, the at least one current adjusting element includes at least one grain boundary. 
     According to an exemplary embodiment, another integrated circuit is provided. The integrated circuit includes a plurality of semiconductor cells, a plurality of sense-amplifiers, and a processing circuit. Each semiconductor cell is configured to represent an address in a mapping table and includes a first input/output end, a second input/output end, a current path and a control end. At least one current adjusting element is disposed in at least one of the current paths to adjust an electrical current. Each sense-amplifier is connected to the second input/output end and configured to sense the electric current from the second input/output end and identify a threshold voltage of the corresponding semiconductor cell. The processing circuit is configured to categorize each of the threshold voltages identified by the corresponding sense-amplifiers into a first state and a second state and mark the state of each of the threshold voltages at the corresponding address in the mapping table. In some embodiments, the at least one current adjusting element includes at least one dopant ion, and at least either the width or the thickness of the current path are defined according to the de Broglie length (DBL), and the length of the current path is longer than the width of the current path. In other embodiments, the at least one current adjusting element includes at least one grain boundary. 
     According to an exemplary embodiment, a code generating method is provided. The code generating method is adopted in an integrated circuit having a plurality semiconductor cells, each of the cells including a first input/output end, a second input/output end and a current path, and at least one current adjusting element is disposed in at least one of the current paths to adjust an electrical current. The method includes: configuring each semiconductor cell to represent an address in a mapping table; determining a read voltage and a reference current; sensing the electric current from the second input/output end and identifying a threshold voltage of the corresponding semiconductor cell; categorizing each of the identified threshold voltages into a first state and a second state; and marking each semiconductor cell at the corresponding address of the mapping table according to the state of the threshold voltages. In some embodiments, the at least one current adjusting element includes at least one dopant ion, and at least either the width or the thickness of the current path are defined according to the de Broglie length (DBL), and the length of the current path is longer than the width of the current path. In other embodiments, the at least one current adjusting element includes at least one grain boundary. 
     According to an exemplary embodiment, the step of categorizing each of the identified threshold voltages into the first state and the second state further includes: categorizing each of the threshold voltages into the first state, the second state, and a third state. 
     According to an exemplary embodiment, a data exchange method is provided. The method may exchange data between a first device and a second device. The second device has a plurality semiconductor cells, each of the semiconductor cells comprising a first input/output end, a second input/output end, a current path, and a control end. The data exchange method includes: providing the first device with a first group of packets for delivery to a second device through a network, in which the first group of packets includes a sequence of read voltages; generating a second group of packets in response to the first group of packets by using the second device, and delivering the second group of packets to the first device; comparing the first group of packets and the second group of packets by using an identity management unit in the first device, and generating a comparison result; and judging whether the second device is permitted to communicate with the first device according to the comparison result. Moreover, the step of generating the second group of packets in response to the first group of packets by using the second device includes: configuring each cell to represent an address in a mapping table; determining a first read voltage and a reference current; sensing an electric current from the second input/output end and identifying a threshold voltage of the corresponding semiconductor cell, wherein at least one current adjusting element is disposed in at least one of the current paths to adjust the electrical current; categorizing each of the threshold voltages into a first state and a second state; and marking each cell at the corresponding address of the mapping table according to the state of the threshold voltages. In some embodiments, the at least one current adjusting element includes at least one dopant ion, and at least either the width or the thickness of the current path are defined according to the de Broglie length (DBL), and the length of the current path is longer than the width of the current path. In other embodiments, the at least one current adjusting element includes at least one grain boundary. 
     In summary, the integrated circuits, code generating methods, and data exchange methods described in the embodiments of the invention can generate physically unclonable identification of a chip. 
     It should be understood, however, that this Summary may not contain all of the aspects and embodiments of the present invention, is not meant to be limiting or restrictive in any manner, and that the invention as disclosed herein is and will be understood by those of ordinary skill in the art to encompass obvious improvements and modifications thereto. 
     In order to make the aforementioned features and advantages of the present invention more comprehensible, embodiments accompanying figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of a key-maintenance module without PUF in the prior art. 
         FIG. 2  illustrates a chip with PUF embedded. 
         FIG. 3  illustrates the concept of PUF. 
         FIGS. 4, 5 and 6  respectively illustrate the originality, the unpredictability and the reproducibility of PUF. 
         FIG. 7  illustrates a management of a chip with PUF. 
         FIG. 8  illustrates a copy protect effect achieved by PUF. 
         FIG. 9  illustrates a Fin transistor with a channel width W around the DBL according to an exemplary embodiment. 
         FIG. 10  illustrates a conduction state of the Fin transistor of  FIG. 9  when a negative ion is present at the source-channel interface according to an exemplary embodiment. 
         FIG. 11  illustrates the structure of an integrated circuit according to a first embodiment of the invention. 
         FIG. 12  illustrates the relationship between the address data and the sensed Vt values of corresponding cells in an example of the invention, in which the Vt fluctuation owing to the random-dopant fluctuation is shown. 
         FIG. 13  illustrates the addressing on a two-dimensional (2D) plane area, in which Address 1, Address 2 . . . and Address 2N are arranged in a mapping table having a checker board pattern according to an exemplary embodiment. 
         FIG. 14  illustrates the distribution of the sensed Vt values of the cells in a case where negative ions are doped in random according to an exemplary embodiment. 
         FIG. 15  illustrates the distribution of the sensed Vt values of the cells in a case where positive ions are doped in random according to an exemplary embodiment. 
         FIG. 16  illustrates an example of the distribution of black and white on the checker board pattern representing the Vt distribution of the cells according to an exemplary embodiment. 
         FIG. 17  illustrates an exemplary device structure according to a second embodiment of the invention, which has a common word line (WL) as a sole gate. 
         FIG. 18  illustrates another exemplary device structure according to the third embodiment of the invention, which has a common WL wrapping the Fins to form a plurality of tri-gate cells. 
         FIG. 19  illustrates the relationship between the read voltage and the lower-Vt peak (W) and the higher-Vt peak (BL) in the Vt distribution according to an exemplary embodiment. 
         FIG. 20  illustrates the relationship between a read voltage with fluctuation, the lower-Vt peak (W), and the higher-Vt peak (BL) according to a fourth embodiment of the invention. 
         FIG. 21  illustrates the cause of the random-telegraph noise (RTN) according to an exemplary embodiment. 
         FIG. 22  illustrates the band diagram when an electron is trapped by an interface trap according to an exemplary embodiment. 
         FIG. 23  illustrates a case where a cell transits from the peak of W to the gap window between W and BL due to the random-telegraph noise (RTN) according to an exemplary embodiment. 
         FIG. 24  illustrates a case where a cell transits from the gap window between W and BL to the peak of W owing to the random-telegraph noise (RTN) according to an exemplary embodiment. 
         FIG. 25  illustrates a case where a cell transits from the peak of BL to the gap window between W and BL due to the random-telegraph noise (RTN) according to an exemplary embodiment. 
         FIG. 26  illustrates a case where a cell transits from the gap window between W and BL to the peak of BL due to the random-telegraph noise (RTN) according to an exemplary embodiment. 
         FIG. 27  illustrates a case where the Vt is changed from in W to a voltage in the gap window lower than the read voltage and returned toward W due to the RTN according to an exemplary embodiment. 
         FIG. 28  illustrates a case where the Vt is changed from in W to a voltage in the gap window higher than the read voltage and returned toward W according to an exemplary embodiment. 
         FIG. 29  illustrates several cases where Vt is changed from inside W toward the gap window according to an exemplary embodiment. 
         FIG. 30  illustrates several cases where Vt is changed from inside the gap window to W according to an exemplary embodiment. 
         FIG. 31  illustrates several cases where Vt is changed from inside BL toward the gap window according to an exemplary embodiment. 
         FIG. 32  illustrates several cases where Vt is changed from inside the gap window to BL according to an exemplary embodiment. 
         FIG. 33  illustrates the procedure of the iterative sensing of a cell transistor (bit) according to an embodiment of the invention. 
         FIG. 34  illustrates a Vt distribution of the cells after the cells are subjected to random doping with negative and positive ions according to a fifth embodiment of the invention. 
         FIGS. 35, 36, 37 and 38  illustrate cases where positive or negative ions are far away from the source edge at the surface of the substrate according to an exemplary embodiment. 
         FIGS. 39 and 40  illustrate two cases where positive and negative ions are canceled out by each other even when the positive and negative ions are present at the source-channel interface according to an exemplary embodiment. 
         FIG. 41  illustrates a RGB checker board pattern showing a 2D mapping table of a Vt distribution in which R, G and B represent different Vt ranges as shown in  FIG. 42  according to another embodiment of the invention. 
         FIG. 42  illustrates the relationship between the Vt-distribution peaks R, G and B and the two read voltages (1) and (2) according to a sixth embodiment of the invention. 
         FIGS. 43 and 44  illustrate a method for removing the random-telegraph noise (RTN) according to the sixth embodiment of the invention. 
         FIG. 45  schematically illustrates the structure of a nano-wire FET-type cell useful in the invention and a drain current of the same, according to an eighth embodiment of the invention. 
         FIG. 46  illustrates a conduction state of the nano-wire FET-type cell when a negative ion is present at the source-channel interface according to an exemplary embodiment. 
         FIG. 47  illustrates a bird&#39;s view of a nano-wire FET-type cell according to an exemplary embodiment. 
         FIG. 48  illustrates a bird&#39;s view of a nano-wire array for constituting a nano-wire FET-type cell array according to an exemplary embodiment. 
         FIG. 49  illustrates a bird&#39;s view of the nano-wire FET-type cell array according to an exemplary embodiment. 
         FIG. 50  illustrates a case where all of the gates of the nano-wire FET-type cells are connected to a sheet-type common word-line (WL) according to an exemplary embodiment. 
         FIG. 51  illustrates a case where the gates of the nano-wire FET-type cells are replaced by a sheet-type common word-line (WL) according to an exemplary embodiment. 
         FIG. 52  illustrates a bird&#39;s view of a tri-gate nano-wire unit cell according to ninth embodiment of the invention. 
         FIG. 53  illustrates an array of the tri-gate nano-wire cells of  FIG. 52 . 
         FIG. 54  illustrates a case where all of the gates of the tri-gate nano-wire cells are connected to a sheet-type common word-line (WL) according to an exemplary embodiment. 
         FIG. 55  illustrates a case where the gates of the tri-gate nano-wire cells are replaced by a sheet-type common word-line (WL) according to an exemplary embodiment. 
         FIG. 56  illustrates a bird&#39;s view of a surrounding-gate nano-wire cell according to an exemplary embodiment. 
         FIG. 57  illustrates an array of the surrounding-gate nano-wire cells of  FIG. 56 . 
         FIG. 58  illustrates a bird&#39;s view of a pillar-type cell according to an exemplary embodiment. 
         FIG. 59  illustrates an array of the pillar-type cell as shown in  FIG. 58  according to an exemplary embodiment. 
         FIG. 60  illustrates a structure of the pillar-type cell array excluding the gates according to an exemplary embodiment. 
         FIG. 61  is a schematic view of grains and grain boundaries of a channel. 
         FIG. 62  illustrates the distribution of the sensed Vt values of the cells with grain boundaries and cells without grain boundaries. 
         FIG. 63  illustrates a Fin transistor with no grain boundary. 
         FIG. 64  illustrates a conduction state of the Fin transistor with a grain boundary located at the source end of the channel. 
         FIG. 65  illustrates a conduction state of the Fin transistor with a grain boundary located at the center of the channel. 
         FIG. 66  illustrates a conduction state of the Fin transistor with a grain boundary located at the drain end of the channel. 
         FIG. 67  is a schematic block diagram of a data exchange system according to an embodiment of the invention. 
         FIG. 68  is a flow diagram of a data exchange method according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Reference now is made to the accompanying drawings to describe the specific embodiments and examples of the invention. Whenever possible, the same reference characters are used in the drawings and the description to refer to the same or like parts. 
     (Random-Dopant Fluctuation, RDF) 
     In the disclosure below, utilizing the random-dopant fluctuation (RDF) for the physically-unclonable function is explained. It has to be noted here that in the following exemplary embodiments, field effect transistors are used as examples to explain the idea of the present invention, and thus a first input/output end may represent a source, a second input/output end may represent a drain, a current path may represent a channel, and a control end may represent a gate; however, the aforementioned embodiments are only used as exemplary examples but not tend to limit the scope of the present invention. In fact, the present invention could also be realized on several other semiconductor devices which are CMOS compatible, such as a bipolar junction transistor (BJT). 
     In order to make the Vt change by ions notable compared to conventional techniques, the channel width W may be shrunk, while the channel length L may not be shrunk. The typical length of W is comparative to the de Broglie length (DBL), which is typically about 9 nm in silicon materials, while the typical length of L is much larger than DBL, for example, more than 100 nm. 
     Several cases where the channel width W is about DBL are discussed below. As illustrated in  FIG. 9 , the electron current flows from the source to the drain across the channel with no ions. 
     If a negative ion is present at the source-channel interface, as illustrated in  FIG. 10 , electrons are reflected by the peak potential of the negative ion. No current flows, because electrons cannot skirt the ion owing to the narrow channel (Si). 
     As mentioned above, the threshold voltage (Vt) is notably affected only when the ion is located at the interface between the source and the drain at the surface of substrate. This feature is made notable by the cell structure proposed in the invention, in which the channel length is larger than the DBL and the channel width is about DBL. 
     In one exemplary embodiment of the invention, the impact of the elementary charge on the potential profile is about 100 mV, a typical electric field across channel layer is about 0.1 MV/cm, which indicates that the impact of the elementary charge located at 10 nm from the interface may vanish. This just coincides with the DBL. In addition, the ion has more impact on the Vt distribution, when the location of the ions in the channel is closer to the source than to the drain; more specifically, the ions is located in the channel within about 10 nm from the source/channel interface. However, it should be noted that the invention is not limited by the aforementioned example. 
     First Embodiment 
       FIG. 11  illustrates an integrated circuit according to a first exemplary embodiment of the invention. In  FIG. 11 , an integrated circuit  700  includes a plurality of field effect transistors and a plurality of sense amplifiers, in which each field effect transistor is configured to represent an address in a mapping table and includes a source, a drain, a channel and a gate. In some exemplary embodiments, in order to minimize source contact as much as possible, a source is shared by two cells and all the sources are connected to a common source line (SL), as shown in  FIG. 11 . Two drains (D) of tandem cells (by which the sources are shared) are independently connected to the sense-amplifiers (S/A). Each of the sense-amplifiers S/A is allocated to the address data (Address 1, Address 2, Address 3 . . . , and Address 2N) in this example. The number of cells is 2N and the number of tandem cells is N. These sense-amplifiers S/A sense the threshold voltage of each cell, i.e., Vt(1), Vt(2), Vt(3), . . . , and Vt(2N). All of the gates are connected to a common word line (WL). In some embodiments, the integrated circuit  700  may also include a processing circuit  750  configured to categorize each of the threshold voltages Vt(1), Vt(2), Vt(3), . . . , and Vt(2N) identified by the corresponding sense-amplifiers S/A into a first state and a second state, and to mark the state of each of the threshold voltages Vt(1), Vt(2), Vt(3), . . . , and Vt(2N) at the corresponding address in the mapping table (e.g., the checker board shown in  FIG. 13  or  FIG. 16 ). However, it should be noted that the processing circuit  750  is not limited to categorizing the threshold voltages into two states, and the processing circuit  750  may also categorize the threshold voltages into three states, for example, depending on the application. 
       FIG. 12  shows the address data in the left and the sensed threshold voltages of the corresponding cells in the right. In this example, n-type MOSFET (p-type channel) is assumed. There are fluctuated threshold voltages around 0.5 V and 0.8 V. This discrepancy comes from a negative ion which exists around source edge at the surface of the silicon substrate. It is regarded that 0.5 V corresponds to the case where a negative ion doesn&#39;t exist around the source edge at the surface of the silicon substrate while 0.8V corresponds to the case where a negative ion exists around the source edge at the surface of the silicon substrate. 
       FIG. 13  illustrates the addressing on a two-dimensional plane area (i.e., the mapping table), in which Address 1, Address 2 . . . and Address 2N are mapped in a checker board pattern. 
       FIG. 14  illustrates a distribution of the sensed threshold voltages. The right peak corresponds to the case where the negative ion exists around the source edge at the surface of the silicon substrate. The tail having the higher Vt comes from a second or more negative ions that exist around the source edge at the surface of the silicon substrate. The other peak corresponds to the case where the negative ion doesn&#39;t exist around the source edge at the surface of the silicon substrate. The cells belonging to the right peak are depicted black (BL) on the checker board, while the other cells are depicted white (W) on the checker board. 
       FIG. 16  illustrates an example of the distribution of black and white on the checker board pattern. The black and white arrangement on the checker board pattern (i.e., the mapping table) is determined by the distribution of the sensed threshold voltages. Since the location of negative ions in device fluctuates among cells, the checker board pattern fluctuates with respect to random-dopant fluctuation. 
     In this embodiment, the negative ion can be replaced with a positive ion. Even in this event, the right peak is black (BL) and the other one is white (W), as illustrated in  FIG. 15 . The following embodiments are essentially unchanged, as long as the black-white checker board pattern (illustrated in  FIG. 16 ) is formed by the random-dopant fluctuation (RDF) in a similar manner. 
     It is also possible to replace the n-type FET (p-channel) with a p-type FET (n-channel). Here “FET” means “field effect transistor”. Even in this event, the right peak is black (BL) and the other is white (W), as illustrated in  FIG. 16 . The following embodiments are essentially unchanged, as long as the black-white checker board pattern ( FIG. 16 ) is made by random-dopant fluctuation (RDF) in a similar manner. 
     Second Embodiment: Device Structure 
       FIG. 17  is a device structure according to the second exemplary embodiment of the invention. There is a plurality of Fin-FETs connected to a common word line (WL). The shape of the WL is a plate shape. Each Fin-FET may satisfy the condition that channel width (W) is around 10 nm, i.e., the de Broglie length (DBL) and the channel length (L) is much larger than 10 nm. Note that the word lines may be independent in a usual system of Fin-FET. There is a gate insulating film between WL and the channel. 
     Third Embodiment: Tri-Gate Type 
       FIG. 18  is another device structure according to a third exemplary embodiment of the invention. There is a plurality of Fin-FETs connected to a common gate. The WL wraps the Fins as shown so that the device structure is a tri-gate. Each Fin-FET may satisfy the condition that channel width (W) is around 10 nm, i.e., the de Broglie Length (DBL) and the channel length (L) is much larger than 10 nm. The gate insulating film also surrounds the Fin layers and is surrounded by the word line (WL). Note that word lines may be independent in a typical Fin-FET system. 
     Fourth Embodiment: Measure Random-Telegraph Noise 
     Each of the sense-amplifiers S/A in  FIG. 11  reads the threshold voltage (Vt) of the corresponding cell as shown in  FIG. 11 . The 2N cells and the 2N sense-amplifiers S/A are grouped with a common word line (WL), as shown in  FIGS. 12, 17 and 18 , and also with a common source-line (SL), as shown in  FIG. 11 . The sensed threshold voltages of the cells in the group are labeled Vt(1), Vt(2), . . . , Vt(2N), wherein each Vt(n) corresponds to Address n, as shown in  FIG. 11 , where n is from 1 to 2N. This corresponding relationship is shown in  FIG. 12 , and the distribution of threshold voltages is divided into two peaks; i.e., the higher-Vt peak (Black, BL) and the lower-Vt peak (White, W), as shown in  FIG. 14 . If the address shown in  FIGS. 11 and 12  is mapped onto a 2D area, as illustrated in  FIG. 13 , a white-black checker board pattern is obtained with respect to the random-dopant fluctuation, as illustrated in  FIG. 16 . 
     To read the threshold voltage, the read voltage is applied by the common word line (WL) shown in  FIGS. 11, 17 and 18 . This read voltage may be higher than the higher tail of the lower Vt peak (W) and lower than the lower tail of the higher Vt peak (BL) in the Vt distribution, as illustrated in  FIG. 19 . 
     Owing to the fluctuation of the word-line shift resistance, it may be necessary to take care of the fluctuation of the read voltage, as illustrated in  FIG. 20 . However, in the exemplary embodiment of the invention, the word line is a common word line (WL) as shown in  FIGS. 11, 17 and 18 , and the shift resistance is very small. 
     A more important sensing issue is the random-telegraph noise (RTN) as described following, which is schematically illustrated in  FIG. 21 . If there are interface shallow traps, electrons are repeatedly trapped by these traps or emitted from these traps. This trap-detrap phenomenon quickly and randomly occurs, and thereby the sensed threshold voltage is fluctuated. The fluctuation amplitude is detectable (about 200 mV) but much smaller than threshold voltage shift which is attributable to ion existing at source side in this exemplary embodiment of the invention. 
     In  FIG. 22 , an electron is trapped by an interface trap. Note that this trap is close to the interface but still in oxide. The pile up of peak barrier around the source edge is decreased as compared with the effect of an ion at the source edge inside the channel. The impact of this trap on the current transport through the channel is thereby smaller than that of an ion at the source side inside the channel, which is shown in  FIG. 10 . 
     As illustrated in  FIG. 23 , it is possible that a cell transits from the peak of W to the gap window between the peak W and the peak BL, but it cannot transfer from the W peak to the BL peak directly because of the small amplitude of Vt shift that is attributable to the random-telegraph noise (RTN). 
     As illustrated in  FIG. 24 , it is possible that a cell transits from the gap window between the W peak and the BL peak to the peak W owing to the random-telegraph noise (RTN). This can be regarded as the counter process of  FIG. 23 . 
     As illustrated in  FIG. 25 , it is possible that a cell transits from the peak BL to the gap window between the peak W and the peak BL, but it cannot transfer from the BL peak to the peak W directly because of the small amplitude of Vt shift that is attributable to the random-telegraph noise (RTN). 
     As illustrated in  FIG. 26 , it is possible that a cell transits from the gap window between the peak W and the peak BL to the peak BL owing to the random-telegraph noise (RTN). This can be regarded as the counter process of  FIG. 25 . 
     Another significant feature of the RTN is that the Vt is repeatedly changed, as shown in  FIGS. 27 and 28 .  FIG. 27  illustrates a case where the Vt is changed from inside the peak W to a voltage in the gap window lower than the read voltage and returned toward the peak W. It is noted that the amplitude of the return is generally different from the amplitude of the first Vt change.  FIG. 28  illustrates a case where the Vt is changed from inside the peak W to a voltage in the gap window higher than the read voltage and returned toward the peak W. It is noted that the amplitude of the return is generally different from the amplitude of the first Vt change. 
     Moreover,  FIG. 29  illustrates several cases where the Vt is changed from inside the peak W toward the gap window. The amplitude of Vt shift is different from each other in general.  FIG. 30  illustrates several cases where the Vt is changed from inside the gap window to the peak W.  FIG. 31  illustrates several cases where the Vt is changed from inside the peak BL toward the gap window.  FIG. 32  illustrates several cases where the Vt is changed from inside the gap window to the peak BL. In the above figures ( FIGS. 29-32 ), the amplitude of Vt shift is different from each other in general and the Vt shift by RTN is larger than the fluctuation of the read bias that is attributable to the lower sheet resistance of the common word line (WL). 
     Accordingly, the Vt fluctuations due to the random-telegraph noise are mitigated. In the invention, the essential idea for removing the impact of the random-telegraph noise (RTN) is by repeated readings of the threshold voltage. Since the Vt shift owing to the RTN is changed in every sensing, as shown in  FIGS. 27 and 28 , the repeated sensing can remove the impact of RTN. This repeated sensing procedure may be performed in all of the cell transistors. 
     The iterative sensing procedure of a cell transistor (bit) is illustrated in  FIG. 33 . Firstly, a cell transistor to be sensed is selected. Subsequently, the number (N) of the iteration of the serial sensing is given, wherein N is typically more than 10. The read voltage and the reference current (Ir) are also given. The read voltage may be higher than the right tail value of the peak W and lower than the left tail value of the peak BL, as illustrated in  FIGS. 27-32 . The reference current typically can be determined by considering the technology node, i.e., the channel length (L). The iteration counters, i, j and k, are all set to zero at the initial condition. Next, the drain current (Id) of the cell transistor (bit) illustrated is sensed, and the first iteration counter (i) is incremented by one, that is, i=i+1. Subsequently, the drain current (Id) is compared with the reference current (Ir). If the absolute value of Id is larger than that of Ir, the second iteration counter (j) is incremented by one; j=j+1. Otherwise, the third iteration counter (k) is incremented by one; k=k+1. Subsequently, the first iteration counter (i) and the number of the iteration of serial sensing (N) are compared. If i&lt;N, the process is returned back to the sensing of drain current, and the first iteration counter (i) is incremented by one again. Otherwise, the second iteration counter (j) is compared with the third iteration counter (k). If j&gt;k, the threshold voltage of the sensed cell belongs to the peak W (white) shown in  FIGS. 14, 19, 20 and 23-32 . Otherwise, the threshold voltage of the sensed cell belongs to the peak BL (black) shown in  FIGS. 14, 19, 20 and 23-32 . Thereafter, another cell transistor is selected, and then the above-mentioned procedure after the first step of selecting a cell transistor to be sensed is repeated until the entire cell transistors (bits) are iteratively sensed according to the above-mentioned procedure. 
     Fifth Embodiment: Expansion to RGB Board 
     As mentioned above, a positive ion at the source edge can also change threshold voltage (Vt), as illustrated in  FIG. 15 , while the direction of the Vt shift becomes opposite to the Vt shift by a negative ion at the source edge. In the disclosure hereafter, the higher Vt peak in the Vt distribution (owing to a negative ion at the source edge) is re-designated as blue (B), which was the peak BL (black) in  FIG. 14 . The lower Vt peak in the Vt distribution (owing to a positive ion at the source edge) is re-designated as red (R), which was the peak W in  FIG. 15 , and the other peak, which was the peak W (white) in  FIG. 14  or the peak BL in  FIG. 15 , is re-designated as green (G), as shown in  FIG. 34  The peak R has a tail in the left owing to 2 or more positive ions at the source side. The peak B has a tail in the right owing to 2 or more negative ions at the source side. The peak G is made of the other cases, including the cases where a positive or negative ion is far away from the source edge at the surface of the substrate as illustrated in  FIGS. 35, 36, 37 and 38 , the cases with the RTN as illustrated in  FIG. 22 , and the cases that positive and negative ions are canceled out by each other even if they exist at the source edge at the surface of the substrate as illustrated in  FIGS. 39 and 40 . Using the same mapping method as illustrated in  FIGS. 12 and 13 , the RGB checker board pattern is obtained, as shown in  FIG. 41 . The RGB checker board pattern has a larger fluctuation on the checker board pattern than the white-black checker board pattern. This implies that the RGB checker board pattern may be preferable even when another doping process is added. 
     Sixth Embodiment: Measure to Random-Telegraph Noise in RGB-Type 
     In order to distinguish R and G, a first read voltage (1) is applied, as illustrated in  FIG. 42 . It is noted that the read voltage (1) is in the gap window between peaks R and G. In order to distinguish G and B, a second read voltage (2) is applied, as illustrated in  FIG. 42 . It is noted that the second read voltage (2) is in the gap window between peaks G and B. If the first sense by the first read voltage (1) and the second sense by the second read voltage (2) return “R” and “G”, respectively, this cell is labeled “R”. If the first sense by the first read voltage (1) and the second sense by the second read voltage (2) return “G” and “G”, respectively, this cell is labeled “G”. If the first sense by the first read voltage (1) and the second sense by the second read voltage (2) return “G” and “B”, respectively, this cell is labeled “B”. 
     The procedure of distinguishing R and G is illustrated in  FIG. 43 . Firstly, a cell transistor (bit) to be sensed is selected. Subsequently, the number (N) of the iteration of the serial sensing is given. The first read voltage (1) and the reference current (Ir) are also given. The first read voltage (1) may be higher than the right tail of the peak R and lower than the left tail of the peak G, as illustrated in  FIG. 42 . The reference current typically can be determined by the technology node, i.e., the channel length (L). The iteration counters, i, j and k, are all set to zero at the initial condition. Next, the drain current (Id) is sensed and the first iteration counter (i) is incremented by one, that is, i=i+1. Subsequently, the drain current (Id) is compared with the reference current (Ir). If the absolute value of Id is larger than that of Ir, the second iteration counter (j) is incremented by one; j=j+1. Otherwise, the third iteration counter (k) is incremented by one; k=k+1. Subsequently, the first iteration counter (i) and N are compared. If i&lt;N, then the process is returned back to the step of sensing the drain current, and the first iteration counter (i) is incremented by one again. Otherwise, the second iteration counter (j) is compared with the third iteration counter (k). If j&gt;k, the threshold voltage of the sensed cell belongs to the red peak (R), as shown in  FIGS. 34 and 42 . Otherwise, the threshold voltage of the sensed cell belongs to the green peak (G) shown in  FIGS. 34 and 42 . 
     The subsequent procedure of distinguishing G and B is illustrated in  FIG. 44 . Firstly, a cell transistor (bit) to be sensed is selected. Subsequently, the number (N) of the iteration of the serial sensing is given. The read voltage and the reference current (Ir) are also given. The second read voltage (2) may be higher than the right tail of the peak G and lower than the left tail of the peak B, as illustrated in  FIG. 42 . The iteration counters, i, j and k, are all set to zero at the initial condition. Next, the drain current (Id) is sensed, and the first iteration counter (i) is incremented by one, that is, i=i+1. Subsequently, the drain current (Id) is compared with the reference current (Ir). If the absolute value of Id is larger than that of Ir, the second iteration counter (j) is incremented by one; j=j+1. Otherwise, the third iteration counter (k) is incremented by one; k=k+1. Subsequently, the first iteration counter (i) and N are compared. If i&lt;N, the process is returned back to the step of sensing the drain current, and the first iteration counter (i) is incremented by one again. Otherwise, the second iteration counter (j) is compared with the third iteration counter (k). If j&gt;k, the threshold voltage of the sensed cell belongs to the green peak (G), as shown in  FIGS. 34 and 42 . Otherwise, the threshold voltage of the sensed cell belongs to the blue peak (B) shown in  FIGS. 34 and 42 . 
     According to the afore-mentioned procedures, if the first sense by the first read voltage (1) and the second sense by the second read voltage (2) return “R” and “G”, respectively, the cell is labeled “R”. If the first sense by the first read voltage (1) and the second sense by the second read voltage (2) return “G” and “G”, respectively, the cell is labeled “G”. If the first sense by the first read voltage (1) and the second sense by the second read voltage (2) return “G” and “B”, respectively, the cell is labeled “B”. Similarly, it can be deduced that:
         If R→G, then return R.   If G→G, then return G.   If G→B, then return B.       

     Thereafter, another cell transistor is selected, and then the above-mentioned procedure after the first step of selecting a cell to be sensed is repeated until all the cell transistors (bits) are iteratively sensed according to the above-mentioned procedure, as illustrated in  FIGS. 43 and 44 . 
     Seventh Embodiment: Fin-FET Cell 
     In the above embodiments, Fin-FET type cells are used in order to make the channel width comparative to the de Broglie length (DBL), although other embodiments of the invention are not limited thereto. 
     Eighth Embodiment: Nano-Wire Cell 
     Next, use of nano-wire FET type cells in the semiconductor device system of the exemplary embodiment of the invention is described below, as illustrated in  FIGS. 45 and 46 . The cross-sectional view in XY plane is the same as in  FIGS. 9 and 10 , in which the channel width (W) is comparative to the de Broglie length (DBL). 
       FIG. 45  illustrates when no ion exists in the channel between the source (S) and the drain (D). The channel length is larger than the DBL, while the channel width (W) and the thickness of the channel silicon layer (Z) are comparative to the DBL. 
     When a negative ion exists at the source edge in the channel, as illustrated in  FIG. 46 , an electron current is reflected by the ion because of no detour, which is similar to the illustration of  FIG. 10 . 
     Since ions cannot exist deep in the vertical direction because of the thin nano-wire, the influence of the ion at the source end of the channel is more enhanced. 
     Similarly, it is possible to gather a plurality of nano-wires each of which includes a source (S), a drain (D), and a channel between the source and the drain, as illustrated in  FIG. 48 . It is noted that the channel width (W) and the silicon channel-layer thickness (Z) are comparative to the de Broglie length (DBL), while the channel length (L) is much longer than de Broglie length (DBL). 
     Similarly, gates can be appended to these nano-wires, as illustrated in  FIG. 49 . The unit cell transistor is illustrated in  FIG. 47 . In order to configure the network of wiring, which is shown in  FIG. 11 , all of the gates should be common. There may be gate insulating film between gate and channel. This is used as a component in the structures of  FIGS. 50 and 51 . In  FIG. 50 , a sheet-shaped common word line (WL) is connected to all of the gates. In  FIG. 51 , all of the gates are replaced by a sheet-shaped common word line (WL). 
     Ninth Embodiment: Tri-Gate Nano-Wire Cell 
     The unit cell transistor of tri-gate nano-wire cells is illustrated in  FIG. 52 . Gate insulating film that covers the nano-wire is covered by the gate.  FIG. 53  illustrates an array of tri-gate nano-wire cells. In order to make the network of wiring, which may be as illustrated in  FIG. 11 , all of the gates should be common. This is realized in the structures illustrated in  FIGS. 54 and 55 . In  FIG. 54 , a sheet-shaped common word line (WL) is connected with all of the gates. In  FIG. 55 , all of the gates are replaced by a sheet-shaped common word line (WL). Furthermore, it is possible to cover the other plane of the cells with another sheet-shaped conductor, as shown in  FIG. 57 . It is preferred that the sheet-shaped conductor mentioned here is a thin-film of polysilicon. The unit cell transistor is illustrated in  FIG. 56 . The gate insulating film that surrounds the nano-wire is surrounded by the gate. 
     It should be noted that the fabrication process of cells like these is suitable to three-dimensional (3D) integration with nano-wire channel and wire-all-around common word line. Thereby, a device-level chip identification can also be proposed in a manner compatible to 3D LSI. 
     Tenth Embodiment: Pillar-Type Cell 
     The above-mentioned nano-wire cells may be replaced by pillar-type cells, as illustrated in  FIG. 58 . The pillar is surrounded by gate insulating film that is further surrounded by the gate. A corresponding cell array is illustrated in  FIG. 59 . It is noted that there is a common word line (WL) which makes a gate-all-around structure of each cell (pillar).  FIG. 60  illustrates the structure of this exemplary embodiment excluding the common word line (WL). The diameter of the pillar should be comparative to the DBL. The source is the substrate to which all the pillars end, and is thereby common to all the cells (pillars). The other end of each pillar is the drain of the cell. There is channel between the source and the drain in each pillar, and further the channel length should be larger than the DBL. The fabrication process of cells like this is suitable to 3D integration with pillar-type channel and a sheet-shaped common word line. Thereby, a device-level chip identification can be also proposed in a manner compatible to three-dimensional LSI. 
     It is preferable that the channel length mentioned above is long enough to make the drain current stable when no ion exists at the source edge in the channel. Typically, the channel length is more than three times the DBL; i.e., 30 nm. 
     Eleventh Embodiment: Grain Boundary 
       FIG. 61  is a schematic view of grains and grain boundaries of a channel. The channel illustrated in  FIG. 61  may be fabricated in the integrated circuit depicted in  FIG. 11 , for example, and the channel may be made of polysilicon. The polysilicon in the channel may be composed of the grains and grain boundaries shown in  FIG. 61 , and the grains may be grown along a vertical direction perpendicular on the surface of a substrate during a thermal process in fabrication. The size of the grains (grain width, Wgr) is therefore sensitive to temperature and the duration of the thermal process. The average grain width is typically from a few ten nanometers to a couple of hundred nanometers, for instance. On the other hand, the width of grain boundary, Wgb, is typically a few nanometers. 
       FIG. 62  illustrates the distribution of the sensed Vt values of the cells with grain boundaries and cells without grain boundaries. As shown in  FIG. 62 , the distribution of the sensed Vt values are decomposed into two peaks, which is caused by positive ions segregated in the grain boundaries, the right peak is sensitive to the gate width dispersion, the gate length dispersion, the word line resistance dispersion, the bit line resistance dispersion, and so on. These dispersions are seen in not only the right peak, but also seen in the left peak. The threshold voltages of the left peak are dispersive because the location and the number of grain boundaries may be probabilistic. For example, the number of grain boundaries may be described with the Poisson distribution. Hereafter in the explanation of this embodiment, the source and the drain are p-type regions and the conducting carriers are holes, however the present invention is not limited to this example. 
     It should be noted that the threshold voltages Vt are lowered by positive ion located at the source end of channel, partially lowered by positive ion located at the center of channel, and is slightly lowered by positive ion located at drain end.  FIG. 63  illustrates a Fin transistor with no grain boundary,  FIG. 64  illustrates a conduction state of the Fin transistor with a grain boundary located at the source end of the channel,  FIG. 65  illustrates a conduction state of the Fin transistor with a grain boundary located at the center of the channel, and  FIG. 66  illustrates a conduction state of the Fin transistor with a grain boundary located at the drain end of the channel. The channel between source (S) and drain (D) may be implemented in a nano-wire structure or a pillar structure of a semiconductor cell, in which the channel has a length L and a thickness Z. 
     In one exemplary embodiment of the invention, the impact of the elementary charge on the potential profile is about 100 mV, a typical electric field across channel layer is about 0.1 MV/cm, which indicates that the impact of the elementary charge located at 10 nm from the interface may vanish. This just coincides with the DBL. In addition, a grain boundary can store several ions, and thus the impact of a grain boundary may vanish at a couple of 10 nm. Therefore, the grain boundary has an impact on the Vt distribution, when the location of the grain boundary in the channel is closer to the source than to the drain. However, it should be noted that the invention is not limited by the aforementioned example. 
     In  FIG. 63 , no hole current is reflected since there is no grain boundary in the transistor. When a grain boundary exists at the source end as shown in  FIG. 64 , the hole current is reflected at the source end of channel owing to the positive charge segregated at the grain boundary at the source end. When a grain boundary exists at the center of the channel, as shown in  FIG. 65 , the hole current is partially reflected by the positive charge segregated at the grain boundary. Moreover, when a grain boundary exists at the drain end of the channel, as shown in  FIG. 66 , the hole current is slightly reflected by the positive charge segregated at the grain boundary. It should be further noted that the number of grain boundaries are not limited to the examples shown. Besides having no grain boundary or one grain boundary in the channel as shown in  FIGS. 63-66 , more than one grain boundaries may exist in the channel. 
     In some embodiments, the grain width Wgr depicted in  FIG. 61  varies along the vertical axis perpendicular to the surface of the substrate above which the channel is fabricated. Therefore, the thickness of channel should be tuned in order to control the average grain width more adequately within the channel layer. In some embodiments, the length of the channel L is between an average grain width and three times the average grain width. Moreover, the thickness of the channel layer may be less than the average grain width of the channel. Furthermore, in some embodiments where the channel is part of a nano-wire structure, the diameter of the nano-wire may be less than the average grain width of the channel. On the other hand, when the channel is part of a pillar structure, the diameter of the pillar may be less than the average grain width of the channel. 
     Twelfth Embodiment: Data Exchange Method 
       FIG. 67  is a schematic block diagram of a data exchange system according to an embodiment of the invention.  FIG. 68  is a flow diagram of a data exchange method according to an embodiment of the invention. With reference to  FIG. 67 , the data exchange system includes a first device  610 , a second device  620 , and a network  650 . The first device  610  may include an identity management unit  630 , and the second device may include an integrated circuit  640 . Moreover, the integrated circuit  640  may be the integrated circuit  700  depicted in  FIG. 11 , for example. On the other hand, the first device  610  may be a data center deciding whether a communication session with the second device  620  is safe, for instance. It should be noted that the number of first device  610  and second device  620  is not limited by the illustration in  FIG. 67 . Referring to  FIGS. 67 and 68 , the system depicted in  FIG. 67  may be used to execute a data exchange method between the first device  610  and the second device  620 . In Step S 700 , the first device  610  provides a first group of packets P1 for delivery to the second device  620  through the network  650 . The first group of packets may include a sequence of read voltages such as gate voltages, for example. It should be emphasized that the network  650  may be any suitable wired or wireless network capable of transferring data packets. In Step S 710 , the integrated circuit  640  of the second device  620  generates a second group of packets P2 in response to the first group of packets. The methods for generating the second group of packets P2 may be referenced to the methods illustrated in  FIG. 33  and  FIGS. 43-44 , for example. The second group of packets P2 are then delivered to the first device  610 . In one embodiment, the first device  610  may send a sequence of gate voltages in the first group of packets P1, and the second device  620  may output a plurality of mapping tables each corresponds to one of the gate voltages respectively in the second group of packets P2. In other words, the second device  620  may generate one mapping table according to one gate voltage sent by the first device  610  using the code generating method illustrated above. The first group of packets P1 and the second group of packets P2 could be decomposed into several packets, the present invention does not limit it. In Step S 720 , the identity management unit  630  in the first device  610  compares the first group of packets P1 and the second group of packets P2 and generates a comparison result. In Step S 730 , the first device  610  then judges whether the second device  620  is permitted to communicate with the first device  610  according to the comparison result. In other words, different gate voltages cause different channel currents in the second device  620 , and different second devices  620  have different channel situation such as different current adjusting elements being disposed in different positions in the channel, and thus the first device  610  could execute the authentication by identifying the same characteristics between the mapping tables in the second group of packets P2. It is noted here that these two packets (first group of packets P1 and second group of packets P2) are independent. In addition, the signal from second device  620  is not subject to any algorithm, because it is made of physical fluctuation of CMOS-PUF. Therefore, it is hard for any hacker to detect a relation between the first group of packets P1 and the second group of packets P2, as long as huge number of packets go and come around the first device  610  in the network. 
     The invention has been disclosed above in the preferred embodiments, but is not limited to those. It is known to persons skilled in the art that some modifications and innovations may be made without departing from the spirit and scope of the invention. Hence, the scope of the invention should be defined by the following claims.