Transient Current Measurement for Advance Materials & Devices

Transcription

1 & Devices 8 May 2017 Brian YEO Application Engineer Keysight Technologies

2 Agenda 2 High speed data acquisition basics Challenges & solutions for transient current measurement. Considerations when making on-wafer transient current measurement Advance material and device characterization Summary

3 High-Speed Data Acquisition Basics 3

4 Measurement Value Steady-State vs Transient Measurement Steady-State Static measurement Easy to measure Wait sufficiently for signal to stabilize before making measurement Long duration steady-state allows for long integration time to improve measurement accuracy Transient Dynamic Measurement Difficult to measure Short transient duration Fast acquisition sacrifices accuracy Transient Steady-State time 4

5 Real-Time Sampling What Real-Time sampling works ADC converts analog waveform to digital data points at rate asynchronous to input waveform data rate Conversion rate is known as sampling rate Sample rate is derived from internal clock signal Input Signal Sample Clock Trigger Signal t s Sample Rate = 1 t s Reconstructed waveform 5

6 Factors Affecting Transient Measurement Term Bandwidth Definition Frequency at which a signal is attenuated by 3 db Sample Rate Rate at which the signal is digitized Memory Depth Amount of memory allocated to a waveform record Acquisition Time Amount of time to acquire waveform 6

7 Steady-State vs Transient Measurement Steady-State & Transient Harmonics Freq Steady-State Freq Transient 7

8 Factors Affecting Transient Measurement Bandwidth Sufficient BW Freq Accurate Result Signal Freq Insufficient BW Inaccurate Result 8

9 Factors Affecting Transient Measurement Bandwidth Harmonic 1st Harmonic Original Signal 9

10 Factors Affecting Transient Measurement Required bandwidth depends on edge speed t r t r Edge Rate is the key determinant when selecting bandwidth 10

11 Factors Affecting Transient Measurement Required bandwidth depends on edge speed Step #1: Determine fastest rise/fall times of device-under-test. Step #2: Determine highest signal frequency content (f knee ). f knee = 0.5/RT (10% - 90%) f knee = 0.4/RT (20% - 80%) Step #3: Determine degree of required measurement accuracy. Step #4: Calculate required bandwidth. Required Accuracy Gaussian Response Maximally-flat Response 20% BW = 1.0 x f knee BW = 1.0 x f knee 10% BW = 1.3 x f knee BW = 1.2 x f knee 3% BW = 1.9 x f knee BW = 1.4 x f knee 11

12 Factors Affecting Transient Measurement Required bandwidth depends on edge speed 60 MHz 100 MHz 350 MHz 500 MHz 12

13 Factors Affecting Transient Measurement Overall bandwidth System bandwidth can be viewed as a chain, where the lowest bandwidth component in the measurement system will limit the bandwidth of the measurement. Fixtures/ Cables Probe Instrument BW effective = 1 BW BW BW n 2 13

14 Attenuation Factors Affecting Transient Measurement Effects of sample rate 0dB -3dB BW Aliased Frequency Components SR=2.5*BW SR=4*BW Frequency 14

15 Challenges & Solutions For Transient Current Measurement 15

16 Fast Low-Current Measurement Challenges Digital Multi-Meter Viable solution to measure current down to 1mA Connection Setup Using DMM Sufficient resolution (>16-bits) Current accuracy is calibrated Current Flow Bandwidth is <100 khz, insufficient to capture current transients in time domain DMM 16

17 Fast Low-Current Measurement Challenges Using An Oscilloscope Current probe limited sensitivity >1mA Shunt resistor limits sensitivity and bandwidth Limited resolution (ADC from 8 to 12 bits) High noise floor due to wide bandwidth Current Probe 17

18 Fast Low-Current Measurement Challenges Limitations with shunt-resistor DUT Parasitic capacitance R C par i T r = 2.2*CR 1 MΩ, 10 pf 22 ms (16 khz) Larger shunt resistance improve sensitivity, but it increases parasitic capacitance which limits the bandwidth Not feasible to switch shunt resistances due to current level changes for optimal sensitivity Current sensitivity is limited by noise floor of oscilloscope 18

19 New Solution To Measure CX3300 Device Current Waveform Analyzer Wide Dynamic Range 14-bit / 16-bit Hardware ADC Wide Bandwidth Fast Sampling Max. 200 MHz 1 GSa/s Low Noise Measurement 150 pa ~ 10 A Analysis Functions CCDF, FFT, Automatic Current Profiler, etc. 19

20 CX3300 Current Sensors & Heads Basic current sensor A1 CX1101A Current Sensor, Single Channel 100 MHz max bandwidth 40 na to 10 A +/- 40 V Common mode voltage Sensor Head required More dynamic range More BW & lower noise A1 A2 CX1102A Current Sensor, Dual Channel 100 MHz max bandwidth 40 na to 1 A +/- 12 V Common mode voltage A1 CX1103A Current Sensor, Low Side 200 MHz max bandwidth 150 pa to 20 ma +/- 0.5 V Common mode voltage Sensor Head required 20

21 CX3300 Sensor Head Connector Type SMA CX1201A CX1202A (with a voltage monitor) CX1203A Furnished with CX1101A and CX1102A CX1204A (shielded twisted pair) CX1205A (test leads) CX1206A Banana plug for 10 A measurement 21

22 Advance CX3300 Current Sensors Conventional Current Shunt DUT CX3300 Current Sensors DUT Low noise amplifier i R i Trade-off between sensitivity and bandwidth Oscilloscope s noise floor limits sensitivity Single resistor limits measurable range High-Frequency Low Current Sensing Circuit Advance sensor technology enables simultaneous wide bandwidth, low current measurement Sensor and mainframe combine to optimize bandwidth, sensitivity and low noise Multiple current ranges supported by the sensors provide wide dynamic range. 22

23 CX3300 Effective Measurement Bandwidth BW effective = 1 BW sensor BW mainframe 2 Sensor Sensor Max BW Mainframe Max BW Effective Measurement BW CX1101A 100 MHz ~ 90 MHz CX1102A 100 MHz 200 MHz ~ 90 MHz CX1103A 200 MHz ~ 140 MHz 23

24 CX3300 Performance vs Current Probe Competitor Current Probe + 12-bit Oscilloscope CX3300 Device Current Waveform Analyzer 100 µs/div 1 ma/div 100 µs/div 1 ma/div?? CX1101A (20 ma range) RMS Noise: 250 µa Bandwidth 100 MHz RMS Noise: 20 µa Bandwidth: 100 MHz 24

25 CX3300 Measurement Performance Pulsed Measurement 100 µa current pulse measured in less than 100 ns 20 ns 100 µa Useful for NVM cell transient characterization 25

26 CX3300 Measurement Performance Advantages of 14/16-bit resolution This area can be magnified. 40 ma 10 μa Anywhere Zoom 26

27 Considerations when making transient current measurement onwafer 27

28 On-Wafer Measurement Considerations Chuck Capacitance Wafer Chuck Chuck to ground capacitance (>1000 pf) - Chuck will charge up with left floating and substrate potential may be unstable during measurement - If pulse generator unit (PGU) is connected to the chuck then it will have long settling time due to the large chuck capacitance Difficult to change chuck voltage quickly Vtop - Use shorting plug to ground wafer chuck (do not leave it floating!) - If chuck requires bias, keep voltage constant throughout measurement Vchuck Alternate method Vtop Vchuck 28

29 On-Wafer Measurement Considerations Probe Contact Resistance High contact resistance and parasitic capacitance degrade pulse shape (significantly) High contact resistance reduces both the pulse amplitude and the current flowing into the DUT Maintain low contact resistance is critical for pulsed measurements 29

30 On-Wafer Measurement Considerations Cable Capacitances Measured I d A 50 W I d Measurement Distortion Cable charging current Rising Edge A 50 W Actual I d less than measured by instrument Falling Edge One way to avoid this issue (other than using short cables) is to measure current at low side as it is close to a stable voltage (zero volts). 30

31 On-Wafer Measurement Considerations Typical Setup Current measurement instrument Parameter analyzer or pulse generator unit (PGU) Shorten the cables as much as possible, and be sure to connect up the circuit common. A 3D positioner is helpful to fix the sensor. 31

32 On-Wafer Measurement Considerations DC Probe Connections To measurement equipment 16493R-101 or 102 To measurement equipment 16493R-202 SSMC(Plug) SMA(m) 200 mm 16493R-202 SSMC(Plug) SMA(m) 200 mm Establishes return path for Gate pulse Advantages: Cheaper than RF probes Bandwidth OK for CX3300 Flexible pad layouts Terminates Well and Source Establishes return path for Drain Current Disadvantages: Minimum achievable pulse width ~100 ns Mechanical tension created on probes Not supported by all prober companies 32

33 On-Wafer Measurement Considerations Actual DC Probe Setup Keep cables as short as possible Connect shields together using a cable to maintain the circuit common and to provide a current return path Current sensor Signal from PG 33

34 On-Wafer Measurement Considerations Shielding to reduce noise Problem: Measurement result is very noisy. External noise from power line, light, electromagnetic waves, etc. prevents accurate measurement. It infiltrates the measurement path via capacitive coupling. Solution: Shield measurement circuit to prevent external noise from permeating the measurement. Shield must be grounded. 34

35 On-Wafer Measurement Considerations Unshielded Shielded 35

36 Advanced Material & Device Characterization 36

37 Device Trends: Lower Power & Higher Speed Advance devices require low-current measurement Examples of innovative devices: Non Volatile Memory (NVM):ReRAM, PRAM, etc. Wide Band Gap Semiconductor: SiC, GaN, etc. Organic devices: OLED, OTFT, etc. Trend and changes for innovative devices: Device characteristics are varied by the timing of the measurement - Time domain current measurement and analysis are becoming important to accelerate device development and debug. Devices are becoming lower power and higher speed. - Need to measure fast low current waveforms to understand the current profile of the low power devices 37

38 Current Advance Material Characterization ReRAM, PRAM ReRAM Set and Reset Cycle Set <100ns Read <100ns Non-transistor based NVM cell characterization requires current measurements faster than 100 ns and lower than 1 ma. 38

39 Advance Material Characterization What are Advanced Non-Volatile Memory Cells These devices consist of special materials and have complex operating mechanisms. To understand device behavior, it is important to measure current flow characteristics between two electrodes. FeRAM PRAM ReRAM Emerging NVM positioning 39

40 Advance Material Characterization Challenges in characterizing advance NVM cells Voltage pulse for ReRAM evaluation Difficult to measure transient current in this short pulse Existing analyzers can measure current here, but < 100 ns < 100 ns Difficult to measure transient current in this short pulse Pulse width: 10 ns to 100 ns Dynamic current: from 1 μa level 1 μa measurement under > 100 MHz BW 40

41 Advance Material Characterization PRAM cell measurement using CX3300 Triangular voltage CX1102 dual channel sensor is used for this measurement. 2 V/div 2 ma/div CX3300 visualizes the phase change by the triangular voltage 2 μs/div Blue : 20 ma range (primary) Magenta: 200 μa range (secondary) 10 μa/div Secondary range captures the behavior in low current domain 41

42 Advance Material Characterization Conventional Power Transistor SI & SiC Si & SiC transistors do not have memory Drain Voltage OFF ON OFF ON Drain Current Time 42

43 Advance Material Characterization GaN transistors GaN transistors remember how long they are in the off state Short Stress Long stress Drain Voltage OFF ON OFF ON Drain Current Time Transient analysis is required to improve performance and reliability 43

44 Advance Material Characterization GaN Current Collapse Measurement Vd off 100 µs Vd off 8.5 ms Pulse Width = 1.5 ms 10 V/div Vd off: 40 V Vd on: 1 V Vg 2 ms/div Current collapse transient can be measured. 1 ma/div Id 44

45 Advance Material Characterization GaN Current Collapse Measurement Vd off 100 ns Vd off 8.5 μs Pulse Width = 1.5 μs 10 V/div Vd off: 40 V Vd on: 1 V 2 μs/div 1 ma/div Vg Id Current response captured with 1 ns sampling rate 45

46 Advance Material Characterization Organic Thin Flim Transistor (OTFT) Improving carrier mobility is one of the key challenges. Need to measure the current levels ranging from na to µa. Switching of OTFT Frequency 1 khz to 10 MHz Vg Id S D OTFT G Current: 1 na to 100 ma 46

47 Summary 47

48 Summary Key Takeaways Total measurement bandwidth is a function of the bandwidth of the individual elements of the measurement setup Conventional measurement instrumentation can measure transient currents down to ~1 ma; smaller current levels require an advance instrument like the CX3300 It is important to take into account all elements (wafer chuck, cables, probes, etc.) of the system when performing high-speed current/voltage measurements on wafer. The CX3300 offers advance capabilities not found on any other high-speed current measurement solution and is especially useful in characterizing many new types of materials and devices. 48

49 Additional Information 49

50 Questions & Answers 50