Flexible Near Field Communication Sensor Labels Built on a Printed Dopant Polysilicon TFT Platform

Transcription

1 Flexible Near Field Communication Sensor Labels Built on a Printed Dopant Polysilicon TFT Platform Soumya Krishnamoorthy, Ashish Shukla, Mao Takashima, Joey Li, Patricia Beck, Atul Wokhlu, Aditi Chandra and Arvind Kamath Thin Film Electronics

2 Overview Introduction Printed dopant polysilicon based TFT System architecture and PIC design Integration and Assembly Measurement results Conclusions

3 Flexible Sensor Label Platform Establish Path to Scalable Flex Hybrid Sensor System Labels Demonstrate 3 different types of sensor labels ADC chip with 3 bits of resolution with a multi-sensor interface Wireless data readout enabled through an NFC interface chip Built on TFE s PDPS (Printed Dopant Polysilicon) TFT process and integrated on plastic substrates with hybrid components Establish pathway to manufacturing RFP Flexible Dual Use Active Sensor Labels

4 Sensor Selection: Market and Technical Assessment Overall Sensor type Strategic Priority / Customer Feedback Technical Assessment & Priority Differentiation vs. existing sensor Key Applications for Thin Film Other Applications Cost Reduction (printed vs. Market Size (printed + standard) conventional)* Printed CAGR: Printed Forecast 2020 Temperature 1 1 Low Humidity 2 2 Low Ethylene 3 5 High Food/Floral, Life Science Food, Small Molecules Drugs Food spoilage/ripeness Industrial Medium $6.05B 65% Tobacco, scientific Medium $800M 75% $25M Plants Medium New New New Pressure (incl vibrations) 4 6 Difficult Medium, if cumulative Vibration, relative weight measurement; Automotive, textile, touch screen, Medium $9.4B 15% $250M Other Gas Sensors (CO2, O2, etc.) 5 None (yet) 4 Low Food Automotive, scientific, indoor air quality Medium O2: $70, CO2: $150M 30% $10M Light 6 Limited 3 Low Supply chain, biologics, tamper evidence Automotive, meteo station Medium $767M 56% $50M *Thin Film market is a sub-set of this market size. Further investigation in progress. Focus on temperature, humidity, and light Focus on food spoilage/ripeness in packaging

5 System Label

6 Sensor Label Overview Antenna Antenna _in ADC<2> ADC<2> VDD_ANA_SNS RCAL RT RP GND NFC ADC<1> ADC<0> ADC<1> ADC<0> CALIBRATE_IN SENSOR_IN OUT_DIS_SENS R4 CALIBB ADC Die A VSNS_SENS VDD_ANA_REF C2 RESETB R1 PBin OUT_DIS_REF R2 GND VBATT VSNS_REF C1 SENSOR LABEL D Battery GN VBATT

7 Label Design and Specification TEMPERATURE SENSOR LABEL HUMIDITY SENSOR LABEL LIGHT SENSOR LABEL Sensor: Thermistor Temperature Range :15 0 C-25 0 C Accuracy = +/ C Sensor: Capacitive Relative Humidity Range :10%-80% Accuracy = ± 10% Sensor: Light Light Range: Lux Accuracy = ± 85Lux

8 Key Process Technology Requirements Low Cost, Low Step-Count Roll-to-Roll Manufacturing Billions - Trillions of low cost units at scale R2R compatible process and assembly Roadmap to lowest step-count and capital cost Maximize printing with excellent overlay capability Hybrid Processing (Lithography) where print cannot yet support critical design rules RF (13.56 MHz) Capable Circuits and Materials High Mobility, low power circuits with adequate transistor density Self-aligned top-gate CMOS Laser crystalized, polysilicon based TFT Thin, unbreakable form factor with low cost and excellent dimensional stability Stainless Steel substrate Printed Semiconductor-grade purity inks and films including Silicon and Dopants

9 Hybrid Process Flow Cross section of CMOS TFT (not to scale)

10 TFT Characteristics

11 Sensor System partition IC 1: ADC IC 2: NFC Sensors Input Interface Clock generation + interface Sampling and measure clocks Control Logic ADC Data bits CLOCK Control Logic 128-bit NFC CRC Generator ADC Common Sensor interface: Translate analog parameter changes (temperature: resistance, humidity: capacitance, light: current) to frequency variations Use a reference frequency to count frequency variations to generate 8 levels of ADC code. Higher resolution/accuracy systems going forward with improved calibration and frequency translation Battery assisted. NFC 8 different 128-bit data streams based on 3- bit ADC input

12 ADC Architecture Overview TREF R1 R2 C2 RCAL R4 C1 RT REFERENCE OSCILLATOR SENSOR OSCILLATOR FREF FOSC IN RESET (N) 10 Bit Counter N = FREF / FOSC ADC BLOCK DIAGRAM (P): Latch calibrated value (N-P) 10-bit 2 s complement adder 3-bit ADC latch ADC OUTPUT TSENS Unpredictable edges Count number of rising TSENS edges = N COUNT As sensor varies measure change in N COUNT ADC code Source of error: Phase between clock edges is unpredictable over time N COUNT ± 1 code hunting We increase internal accuracy by 2 bits internally and truncate the LSB to give final 3 bit ADC output Increasing ADC resolution internally to 5b provides margin for other variations Oscillator delays: Not significant at 3-bit level

13 Temp Sensor: Ideal 5 bit ADC output (no error sources) Thermistor resistance variation with temperature Processed to a 5-bit ADC code Leads to oscillator frequency variation with temperature Count variation as a function of temperature

14 Impact of Mismatch and Variations Variation in Sens Oscillator frequencies Reference Oscillator frequency variation <10% Variation in Sens Oscillator absolute count

15 Adding error sources: 5b to 3b conversion 5b to 3b Design margin at 5b used to compensate for error sources VARIATION IN 5-bit COUNT Error sources included: External components (die to die): RT (1.43%), R1 (0.1%), C1(1%) Comparator offset 150mV (3sigma) Comparator delay mean=40us, 100us (3sigma) Code hunting included Reference clock variation = 1Hz +/-10% (due to comparator offset and delay, external components) VARIATION IN 3-bit CODE Internal 5b design creates design margin truncate to 3b code Ideal count = 110 Yield at 22.5deg = 87% (similar at other temperatures)

16 ADC PIC Layout PMU Oscillators Digital Calibration and Arithmetic

17 NFC IC Architecture Overview Design streams out 8 different 128-bit CRC validated payloads depending on the state of the sense pins. NFC IC is energized by a smart phone ADC data is sampled by the NFC IC to secure a successful read within a certain duration.

18 NFC PIC Layout T O A N T E N N A Ground Antenna Rectifier ROM Counter Level Shifter D0 D1 D2 A D C I N P U T S VDD

19 Load Modulation for Half Wave Rectifier Data stream (128-b payload) Manchester encoded data Load modulation at antenna terminals on tag Load modulation at receiver

20 NFC Label- Data Readout 128-b NFC payload with different ADC outputs 128 bits B7 FF B7 FF B7 FF B7 FF B7 FF B7 FF L CRC (L) CRC (L) ADC code Sensor ID - Allows 2 8 unique ID s L = Laser (UID) CRC is also Laser 5b Bit ADC code: D2, D1, D0 B7FFB7FFB7FFB7FFB7FFB7FF0000CE7F B7FFB7FFB7FFB7FFB7FFB7FF0001DFF6 B7FFB7FFB7FFB7FFB7FFB7FF0002ED6D B7FFB7FFB7FFB7FFB7FFB7FF0003FCE4 B7FFB7FFB7FFB7FFB7FFB7FF B B7FFB7FFB7FFB7FFB7FFB7FF000599D2 B7FFB7FFB7FFB7FFB7FFB7FF0006AB49 B7FFB7FFB7FFB7FFB7FFB7FF0007BAC0 Application SW on the reader (smartphone) to interpret C C C C C C C C C C C C C C > C For TEMPERATURE SENSOR LABEL

21 NFC Interface and Application Software Initial NFC read verification using a handheld NFC reader Sensor Level 0 A small custom application was built for Android mobile phone devices to interpret and translate the 128-bit NFC payload with different ADC outputs Flextech Information NFC ID Sensor data display ADC/Sensor Level (Code 0-7) Read Range > 2cm on Android phone

22 Assembly Label attach and integration process flow developed Materials chosen shown to be compatible with circuit metallization Electrical / physical compatibility study onto flexible substrates PICs, passive components, battery and sensors integrated onto plastic Benchtop measurements of components pre/post assembly

23 Process Flow for Label Integration Description of Process Flow SAM10(Self Assembly Material Sn/Bi, Tamura Japan) Enable reliable attach Cu/PET backplane Stencil print SAM10 Attach discrete/sensor/pic PET SAM10 SAM10 Reduce mis-attach and improve yield Minimize attach step and material number Reflow in Oven Compatible between various component. PET compatible process. Dispense Ag epoxy Attach display 60C cure

24 Assembly Cross section of the die assembly Antenna and components combined on copper backplane

25 Reliability Testing Flexible test backplanes undergo functionality and reliability testing Minimum bend radius ~25mm around printed IC on flex Sensors are tested pre/post assembly to ensure no change to sensor performance

26 Temperature Sensor Measurement - Test Setup Temperature readout Water bath with additional calibration thermometer Labels are placed in vacuum bags are submersed Direct electrical connections out, or RF output also possible NFC read through water Code read through NFC interface

27 Temperature Sensor Measurements ADC output code ADC output code Vs Temperature Temperature in 0 C Label 1 Label 2 Label 3 Label 4 Label 5 Fref~ 1Hz Fsens~450Hz 8 distinct ADC codes read out through NFC interface corresponding to temperatures from 15C to 30C with o C LSB

28 Light Sensor Measurement - Test Setup LED light source Sensor for LUX meter Label with light sensor Calibration between light sensed by LUX meter sensor and label sensor needs to be performed Expect non-linearity in ADC code Vs Lux without calibration Labels are placed into a light box. NFC phone read occurs from outside the closed box

29 Light Sensor Measurement 8 ADC codes read out through NFC interface corresponding to different light intensities Non linearity due to LUX meter calibration issue

30 Light Sensor Measurements ADC Code 3 Bit ADC Code Vs Light Intensity Intensity (LUX) Label 1 Label 2 Label 3 Fref~ 10Hz Fsens~200Hz 8 distinct ADC codes read out through NFC interface corresponding to light intensities from LUX

31 Humidity Sensor Measurements: Test Setup Moist and dry air source Controlling humidity External humidity meter Labels are placed into a Humidity box. NFC phone read occurs from outside the closed box

32 Humidity Sensor Measurements Measured 3 Bit ADC Code Vs % Relative Humdity 3 Bit ADC Code % Relative Humidity (%RH) Fref~ 4.5Hz Fsens~1.5KHz 8 ADC codes read out through NFC interface corresponding to different humidity levels Data collection across multiple labels in progress

33 Conclusions Demonstrated 3 types of NFC sensor labels with 3 bits of resolution A 3 bit ADC with an NFC interface has been demonstrated On chip calibration as a method to address process variation has been achieved Multi-bit communication across the two dies has been successfully achieved Android mobile phone app developed to display sensor data and state for all 3 sensor labels Built with TFE s PDPS (printed dopant polysilicon) TFT process Integrated on plastic substrates with hybrid components Hybrid flexible assembly encompassing multiple form factors (steel, SMT, battery, start buttons) has been demonstrated using a two part solder/epoxy system Reliability demonstrated using this process Opens up path for wide variety of applications in the flexible wireless space Thanks to Flextech for support!