Patent Publication Number: US-7710240-B2

Title: RFID device having nonvolatile ferroelectric capacitor

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a RFID device having a nonvolatile ferroelectric capacitor, and more specifically, to a technology of reducing the whole size of a RFID device using a nonvolatile ferroelectric capacitor formed by the same process as that of a memory cell capacitor. 
   2. Description of the Related Art 
   Generally, a ferroelectric random access memory (hereinafter, referred to as ‘FeRAM’) has attracted considerable attention as next generation memory device because it has a data processing speed as fast as a Dynamic Random Access Memory (hereinafter, referred to as ‘DRAM’) and preserves data even after the power is turned off. 
   The FeRAM having structures similar to the DRAM includes the capacitors made of a ferroelectric substance, so that it utilizes the high residual polarization characteristic of the ferroelectric substance in which data is not deleted even after an electric field is eliminated. 
   Meanwhile, a general Radio Frequency Identification device (hereinafter, referred to as “RFID”) comprises a modulator and a demodulator for modulating and demodulating a radio frequency signal and a voltage multiplier for generating a power voltage. 
   A conventional capacitor used in the voltage multiplier, the modulator and the demodulator has a PIP (Poly-Insulator-Poly) structure. Preferably, an insulator is SiO 2  or Al 2 O 3  which is an upper dielectric material. 
   However, since the above-described upper dielectric materials have a small dielectric constant, a large number of capacitors are used to obtain desired capacitance. As a result, the whole chip area is increased. 
   The conventional capacitor used in the voltage multiplier, the modulator and the demodulator is formed by a different process than that of a cell capacitor of a memory. Thus, rendering the fabrication process increasingly complicated and costly. 
   SUMMARY OF THE INVENTION 
   Various embodiments of the present invention provide method of fabricating all of the capacitors used in a RFID device as nonvolatile ferroelectric capacitors using the same process for manufacturing cell capacitors in order to reduce the size of the RFID device. 
   According to one embodiment of the present invention, a RFID device comprises an antenna configured to transmit and receive a radio frequency signal to/from an external communication apparatus, an analog block including a voltage multiplier configured to generate a power voltage depending on the radio frequency signal received through the antenna, a digital block configured to receive the power voltage, process the radio frequency signal received through the antenna, and transmit a response signal to the analog block, and a memory configured to store data. Preferably, the voltage multiplier comprises a plurality of rectification units each configured to rectify the radio frequency signal applied through the antenna, and a plurality of charge pumping units each configured to include a plurality of nonvolatile ferroelectric capacitors and to charge-pump a voltage rectified in the plurality of rectification units. 
   According to another embodiment of the present invention, a RFID device comprises an antenna configured to transmit and receive a radio frequency signal from an external communication apparatus, an analog block including a demodulator configured to demodulate an operating command signal in response to the radio frequency signal received through the antenna, a digital block configured to receive the operating command signal and process data received through the antenna to transmit a response signal to the analog block, and a memory configured to store the data. Preferably, the demodulator comprises a plurality of rectification units each configured to rectify the radio frequency signal applied through the antenna, and a plurality of charge pumping units each configured to include a plurality of nonvolatile ferroelectric capacitors and to charge-pump a voltage rectified in the plurality of rectification units. 
   According to still another embodiment of the present invention, a RFID device comprises an antenna configured to transmit and receive a radio frequency signal from an external communication apparatus, an analog block including a modulator configured to modulate a response signal and output the radio frequency signal through the antenna, a digital block configured to process the radio frequency signal received through the antenna and transmit the response signal to the analog block, and a memory configured to store data. Preferably, the modulator comprises a modulator driving unit configured to output a modulator driving signal in response to the response signal, and an input impedance modulation unit configured to include a plurality of serially connected nonvolatile ferroelectric capacitors and change input impedance in response to the modulator driving signal. 
   According to still another embodiment of the present invention, a RFID device comprises an antenna configured to transmit and receive a radio frequency signal from an external communication apparatus, an analog block including a voltage multiplier configured to generate a power voltage in response to a radio frequency signal received through the antenna, a demodulator configured to demodulate an operating command signal in response to the radio frequency signal received through the antenna, and a modulator configured to modulate a response signal and output the radio frequency signal through the antenna, a digital block configured to receive the operating command signal by the power voltage and process data to transmit the response signal to the analog block, and a memory configured to store the data. Preferably, the voltage multiplier comprises a plurality of rectification units each configured to rectify the radio frequency signal applied through the antenna, and a plurality of charge pumping units each configured to include a plurality of first nonvolatile ferroelectric capacitors and to charge-pump a voltage rectified in the plurality of rectification units. The demodulator comprises a plurality of rectification units each configured to rectify a radio frequency signal applied through the antenna and a plurality of charge pumping units each configured to include a plurality of second nonvolatile ferroelectric capacitors and to charge-pump a voltage rectified in the plurality of rectification units. The modulator comprises a modulator driving unit configured to output a modulator driving signal in response to the response signal, and an input impedance modulation unit configured to include a plurality of third nonvolatile ferroelectric capacitors and to change input impedance in response to the modulator driving signal and transmit a phase-changed signal to the antenna. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other aspects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
       FIG. 1  is a block diagram illustrating a RFID device according to an embodiment of the present invention; 
       FIG. 2  is a circuit diagram illustrating an example of a voltage multiplier of  FIG. 1 ; 
       FIG. 3  is a circuit diagram illustrating another example of a voltage multiplier of  FIG. 1 ; 
       FIG. 4  is a waveform diagram illustrating an output voltage of the voltage multiplier of  FIGS. 2 and 3 ; 
       FIG. 5  is a circuit diagram illustrating an example of an envelope detector used in a demodulator of  FIG. 1 ; 
       FIG. 6  is a circuit diagram illustrating another example of an envelope detector used in a demodulator of  FIG. 1 ; 
       FIG. 7  is a waveform diagram illustrating an output voltage of the envelope detector of  FIGS. 5 and 6 ; 
       FIG. 8  is a block diagram illustrating a modulator of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
   The present invention will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     FIG. 1  is a block diagram illustrating a RFID device according to an embodiment of the present invention. 
   In this embodiment, the RFID device comprises an antenna  10 , an analog block  20 , a digital block  30  and a memory  40 . 
   The antenna  10  transmits and receives data with an external reader or writer in response to a radio frequency signal. 
   The analog block  20  comprises a voltage multiplier  21 , a voltage limiter  22 , a modulator  23 , a demodulator  24 , a voltage doubler  25 , a power-on reset unit  26  and a clock generating unit  27 . 
   The voltage multiplier  21  is connected to the antenna  10  through terminals A, A′ and generates a power voltage VDD of the RFID device in response the radio frequency signal applied from the antenna  10 . 
   The voltage limiter  22  is connected to the antenna  10  through the terminals A, A′ and limits a voltage of the radio frequency signal applied from the antenna  10 . 
   The modulator  23  is connected to the antenna  10  through the terminals A, A′ and modulates a response signal Response applied from the digital block  30  to transmit the signal to the antenna  10 . 
   The demodulator  24  is connected to the antenna  10  through the terminals A, A′ and detects an operating command signal from the radio frequency signal applied from the antenna  10  by the power voltage VDD to output a command signal CDM to the digital block  30 . 
   The voltage doubler  25  boosts the power voltage VDD applied from the voltage multiplier  21  to supply a boosting voltage VDD 2  having a swing width twice larger than that of the power voltage VDD to the memory  40 . 
   The power-on reset unit  26  senses the power voltage VDD applied from the voltage multiplier  21  to output a power-on reset signal POR for controlling a reset operation to the digital block  30 . 
   The clock generating unit  27  generates a clock signal CLK by the power voltage VDD. 
   The digital block  30  receives the power voltage VDD, the power-on reset signal POR, the clock signal and the command signal CMD from the analog block  20  to output the response signal Response to the analog block  20 . The digital block  30  outputs an address ADD, data I/O, a control signal CTR and a clock signal CLK to the memory  40 . 
   The memory  40  comprises a plurality of memory cells each including a nonvolatile ferroelectric capacitor. 
     FIG. 2  is a circuit diagram illustrating an example of the voltage multiplier  21  of  FIG. 1 . 
   The voltage multiplier  21  comprises a plurality of schottky diodes D 1 ˜D 6 , a plurality of nonvolatile ferroelectric capacitors FC 1 ˜FC 6  and a stress preventing circuit  211 . The stress preventing circuit  211  comprises a plurality of nonvolatile ferroelectric capacitors FC 7 ˜FC 8 . 
   The voltage multiplier  21  outputs the power voltage VDD to an output terminal by a rectification operation and a charge pumping operation when the radio frequency signal is received from the antenna  10 . The rectification operation is performed in the plurality of schottky diodes D 1 ˜D 6 , and the charge pumping operation is performed in the plurality of nonvolatile ferroelectric capacitors FC 1 ˜FC 8 . The power voltage is an operating voltage of the RFID device. 
   Charges are stored in the nonvolatile ferroelectric capacitor FC 2  by the rectification operation of the diodes D 1  and D 2 . The charges stored in the nonvolatile ferroelectric capacitor FC 2  are pumped by the rectification operation of the diodes D 3  and D 4 , and stored in the nonvolatile ferroelectric capacitor FC 4 . The rectification operation and the pumping operation are sequentially performed to generate the power voltage VDD through the diodes D 5  and D 6  of the final terminal. 
   When a voltage greater than a threshold voltage is applied to the plurality of nonvolatile ferroelectric capacitors FC 1 ˜FC 6 , dielectric materials of the plurality of nonvolatile ferroelectric capacitors FC 1 ˜FC 6  are damaged by voltage stress and increases leakage current. 
   To prevent increase of leakage current, the stress preventing circuit  211  prevents a voltage over the threshold voltage (for example, about 0.5V) from being applied to the plurality of nonvolatile ferroelectric capacitors FC 1 ˜FC 6 . 
   The stress preventing circuit  211  comprises a plurality of serially connected nonvolatile ferroelectric capacitors FC 7 ˜FC 8  each having a predetermined voltage (for example, about 0.5V) between a power voltage VDD output terminal and a ground voltage VSS output terminal. 
   As a result, the voltage stress greater than the threshold voltage is prevented from being applied to the plurality of nonvolatile ferroelectric capacitors FC 1 ˜FC 6 , so that the power voltage VDD is operated only in a stabilized intrinsic area. 
     FIG. 3  is a circuit diagram illustrating another example of the voltage multiplier  21  of  FIG. 1 . 
   The voltage multiplier  21  comprises a plurality of schottky diodes D 7 ˜D 14 , a plurality of nonvolatile ferroelectric capacitors FC 9 ˜FC 14  and the stress preventing circuit  211 . The stress preventing circuit  211  comprises a plurality of nonvolatile ferroelectric capacitors FC 15 ˜FC 16 . 
   The voltage multiplier  21  has a different connection relationship of diodes and capacitors from that of  FIG. 2 . In other words, one terminal of the nonvolatile ferroelectric capacitor FC 9  is connected to the other terminal of the nonvolatile ferroelectric capacitor FC 10  through the diode D 8 , and one terminal of the nonvolatile ferroelectric capacitor FC 10  is connected to the other terminal of the nonvolatile ferroelectric capacitor FC 9  through the diode D 7 . The connection relationship of the nonvolatile ferroelectric capacitors FC 11 ˜FC 14  and the diodes D 9 ˜D 12  is the same as that of the nonvolatile ferroelectric capacitors FC 9  and FC 10  and the diodes D 7  and D 8 . The power voltage VDD is generated through the diodes D 13  and D 14  of the final terminal. 
   The voltage multiplier  21  generates the power voltage VDD by the rectification operation and the charge pumping operation when the radio frequency signal is applied from the antenna  10 . The rectification operation is performed by the plurality of schottky diodes D 7 ˜D 14 . The charge pumping operation is performed by the plurality of the plurality of nonvolatile ferroelectric capacitors FC 9 ˜FC 14 . The power voltage VDD is an operating voltage of the RFID device. 
   When a voltage greater than a threshold voltage is applied to the plurality of nonvolatile ferroelectric capacitors FC 9 ˜FC 14 , dielectric materials of the plurality of nonvolatile ferroelectric capacitors FC 9 ˜FC 14  are damaged by voltage stress and increases leakage current. 
   To prevent increase of leakage current, the stress preventing circuit  211  prevents a voltage over the threshold voltage (for example, about 0.5V) from being applied to the plurality of nonvolatile ferroelectric capacitors FC 9 ˜FC 14 . 
   The stress preventing circuit  211  comprises a plurality of serially connected nonvolatile ferroelectric capacitors FC 15 ˜FC 16  each having a predetermined voltage (for example, about 0.5V) between the power voltage VDD output terminal and the ground voltage VSS output terminal. 
   As a result, the voltage stress greater than the threshold voltage is prevented from being applied to the plurality of nonvolatile ferroelectric capacitors FC 9 ˜FC 14 , so that the power voltage VDD is operated only in a stabilized intrinsic area. 
     FIG. 4  is a waveform diagram illustrating the power voltage VDD generated from the voltage multiplier  21  of  FIGS. 2 and 3 . 
   Referring to  FIG. 4 , when the radio frequency signal of 900 MHz is applied from the antenna  10 , it is shown that the power voltage VDD outputted from the voltage multiplier  21  is about 1.4V while a peak-to-peak input voltage is 200 mV and an output current is 10 μA. 
     FIG. 5  is a circuit diagram illustrating an example of an envelope detector  28  used in the demodulator  24  of  FIG. 1 . 
   The envelope detector  28  of  FIG. 5  comprises a plurality of schottky diodes D 15 ˜D 18 , a plurality of nonvolatile ferroelectric capacitors FC 17 ˜FC 20  and a resistor R 1 . 
   The envelope detector  28  stores charges in the nonvolatile ferroelectric capacitor FC 19  by the rectification operation of the diodes D 15  and D 16 , and pumps charges stored in the nonvolatile ferroelectric capacitor FC 19  by the rectification operation of the diodes D 17  and D 18  to store the pumped charges in the nonvolatile ferroelectric capacitor FC 20 . These rectification and pumping operations are sequentially performed to output an output voltage Vout. The resistor R 1  is positioned between an output terminal and a ground terminal. 
   The envelope detector  28  outputs the command signal CMD having a level of the output voltage Vout to the digital block  30  by the rectification operation of the plurality of schottky diodes D 15 ˜D 18  and the charge-pumping operation of the plurality of nonvolatile ferroelectric capacitors FC 15 ˜FC 20  when the radio frequency signal is applied from the antenna  10 . 
   The number of the diodes D 15 ˜D 18  of the envelope detector  28  is limited in four, so that the output voltage Vout is limited in a low voltage. 
   Preferably, the capacitance of the nonvolatile ferroelectric capacitors FC 17 ˜FC 20  is designed to be smaller than that of the capacitor used in the voltage multiplier  21 . 
     FIG. 6  is a circuit diagram illustrating another example of an envelope detector  28  used in the demodulator  24  of  FIG. 1 . 
   The envelope detector  28  of  FIG. 6  comprises a plurality of schottky diodes D 19 ˜D 23 , a plurality of nonvolatile ferroelectric capacitors FC 21 ˜FC 25 , and a resistor R 2 . 
   The envelope detector  28  of  FIG. 6  has a different diode and capacitor connection relationship from that of  FIG. 5 . That is, one terminal of the nonvolatile ferroelectric capacitor FC 21  is connected to the other terminal of the nonvolatile ferroelectric capacitor FC 22  through the diode D 20 , and one terminal of the nonvolatile ferroelectric capacitor FC 22  is connected to the other terminal of the nonvolatile ferroelectric capacitor FC 21  through the diode D 19 . The connection relationship of the nonvolatile ferroelectric capacitors FC 23 , FC 24  and the diodes D 21 , D 22  is the same as that of the nonvolatile ferroelectric capacitors FC 21 , FC 22  and the diodes D 19 , D 20 . The output voltage Vout is stored in the nonvolatile ferroelectric capacitor FC 25  through the diodes D 23 , D 24  of the final terminal. 
   The above-described envelope detector  60  outputs the command signal CMD having a level of the output voltage Vout to the digital block  30  by the rectification operation of the plurality of schottky diodes D 19 ˜D 23  and the charge-pumping operation of the plurality of nonvolatile ferroelectric capacitors FC 21 ˜FC 24  when the radio frequency signal is applied from the antenna  10 . 
   The number of the diodes D 19 ˜D 22  of the envelope detector  28  is limited in four, so that the output voltage Vout is limited in a low voltage. 
   Preferably, the capacitance of the nonvolatile ferroelectric capacitors FC 21 ˜FC 24  is designed to be smaller than that of the capacitor used in the voltage multiplier  21 . 
     FIG. 7  is a waveform diagram illustrating an output voltage of the envelope detector  28  of  FIGS. 5 and 6 . 
   Referring to  FIG. 7 , the envelope detector  28  outputs the command signal CMD having a level of the output voltage Vout when it receives the radio frequency signal from the antenna  10  to sense the operating command signal. 
     FIG. 8  is a block diagram illustrating the modulator  23  of  FIG. 1 . 
   The modulator  23  comprises an input impedance modulation unit  231  and a modulator driving unit  232 . The input impedance modulation unit  231  comprises a plurality of serially connected nonvolatile ferroelectric capacitors FC 26 ˜FC 28  each configured to receive an output signal of the modulator driving unit  232  through each command connection terminal. 
   The modulating operation of the modulator  23  is performed by a backscatter operation. That is, the modulator driving unit  232  outputs a modulator driving signal to the input impedance modulation unit  231  in response to the response signal Response applied from the digital block  30 . 
   When a backward connection is activated, a reader transmits a carrier signal having a continuous frequency. Then, the input impedance modulation unit  231  changes input impedance to modulate the radio frequency signal backscattered from the antenna  10 . As a result, the modulator  23  changes input capacitance and performs a phase modulation to transmit the backscattered radio frequency signal to an external reader through the antenna  10 . 
   The nonvolatile ferroelectric capacitor utilized in the present embodiment of the present invention is formed by the same process as that of a capacitor of a memory cell. As a dielectric material of the capacitor, SrBi 2 Ta 2 O 9  (SBT) or PbZrTiO (PZT) which have a high dielectric constant is used. The dielectric constant of the SBT is 250, and the dielectric constant of the PZT is 500. As a result, the area of the capacitor used in the RFID device can be reduced. 
   As described above, a capacitor used in a RFID device according to an embodiment of the present invention is formed by the same process as that of a memory cell to simplify the process. 
   In addition, the capacitor has a high dielectric constant to reduce the whole size of the RFID device. 
   The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. Thus, the embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.