Curve Tracer Design for Semiconductor Components Measurement

Transcription

1 JURNAL TEKNIK POMITS Vol. 1, No. 1, (2013) Curve Tracer Design for Semiconductor Components Measurement Dionisius Adrianta Wardhana and Devy Kuswidiastuti Jurusan Teknik Elektro, Fakultas Teknologi Industri, Institut Teknologi Sepuluh Nopember (ITS) Jl. Arief Rahman Hakim, Surabaya adrianta_w@mhs.ee.its.ac.id, devy@ee.its.ac.id Abstract For years, NXP Semiconductors has tried to develop a curve tracer, designated for measuring returning semiconductor products from the customer. It is intended to produce fast and efficient measurement result. The curve tracer is used to measure a diode within required time. It is built on two parts, hardware and software, which both of them were designed on EDA based software called Altium Designer Keywords: Curve Tracer, Hardware Design, Software Design, Diode, Altium Designer N I. INTRODUCTION XP has shipped more than one billion chips worldwide within the last 10 years [1]. Great ratio of these chips belongs to the automotive segment of the company business unit. Mainly operated by the Business Unit Automotive which located at Nijmegen, the company researches and makes hundreds electrical components and devices for automotive purposes, such as CAN, LIN, and Flexray Board. To maintain the customers satisfaction, NXP always welcomes the returning products because of the manufacturing faults. However, in the recent times NXP feels the inefficiency of returning products because it needs to check every returning product for specific reason. This costs a lot of time, money, and resources. Therefore, NXP realizes that it needs a better solution for minimizing all the costs. Then, it comes out with an idea of using a semiconductor curve tracer. Curve tracer is a piece of electronic test equipment which function is to analyze the characteristic of semiconductor instrument. The device under test (DUT) can also be triggered by specific voltage and current to view the curve performance of the instrument. The curve later can be compared with the ideal curve of the component to examine if the component works correctly. In this project, the curve tracer was intended to conduct measurement of a diode. The diode has a specific function as an ESD (Electrostatic Discharge) protector in most of the components manufactured by NXP BU Automotive. Since 80 % of the returning products failure is caused by the damaged ESD protection component which is a diode it is going to be more efficient if NXP recognize the problem before the customers send back the products. This solution undoubtedly will provide faster, cheaper, and more efficient way to do a testing. Still, the available curve tracer on the market is a big, complex, and expensive machine which is not suitable for placing in hundreds NXP s customers. Hence, NXP decide to make its own curve tracer which is more compact in size, low-cost, and human friendly. Although this idea has been realized since 3 year ago, the final product, which is also made by previous intern students, has not met the requirements from NXP. Since the measurement time still took prolonged time, a demand for producing better version of a curve tracer has been emerged. Therefore, this year the assignment is about designing a curve tracer which can generate faster measurement time. Ideally the measurement time for each pin should be lower than 4 seconds. To speed up the measurement time, there are two possible solutions. The first one is improving the method from last year, which use DC sweep as an input of the curve tracer. Meanwhile, the second option is to use AC waveform as an input. Different kinds of waveforms can be used, such as sine wave or saw tooth wave. Both of the solutions undoubtedly will provide faster measurement results than the previous curve tracer. Both methods will be divided to hardware and software parts. The hardware part function is to make the measurement voltage compatible with the software whereas the software part will works as calculation and plotting tools. As this project is specifically built based on the Altium software, an electronic design tools for engineer [2], all of this designing part will be accomplished by using it. Wide variety of tools built in the Altium designer, for example, PCB designer and FPGA programming software, will be used in this project. II. ASSIGNMENT A. Initial Situation Curve tracer is an electrical test equipment unit used for graphing a function by plotting points and analyzing symmetries, derivatives, and so on. A curve tracer is usually used to measure semiconductors components, such as, diodes, resistors, and capacitors. As a chips-maker, NXP produces thousands of components in a period and for every component produced, it needs to be checked whether it works properly or not. Therefore, there is a need of a curve tracer which has a short measurement time. Since the previous curve tracer did not make the least required time to measure a component, there is a demand to improve

2 JURNAL TEKNIK POMITS Vol. 1, No. 1, (2013) the curve tracer to meet the appropriated time. The required time to measure 32 pins component is approximately 2 minutes in total. Then for measuring 1 single pin, likened as a diode, it takes almost 4 seconds. The curve tracer will works by sweeping (automatically continuously varying with time) voltage into its terminal input of the DUT. Then, it measures the current s load or voltage which the device allows to flow and make a graph out of it. A V-I (Voltage versus current) graph is obtained by the sweep, displayed on a screen, and will be compared with the ideal graph to see whether the device works correctly or not. To speed up the measurement process, a varying input signal can be used, either a static or dynamic signal. The problem is whether the signal compatible with the ADC and DAC used in the NB3000 board, a FPGA-platform device which is manufactured by Altium. Since the ADC and DAC on this board, which is used to supply and read signals, can only works in the range of 0 to 5V, a shifter circuit is needed to adjust the signal coming in and out from the ADC and DAC. For displaying the correct graph on the screen of NB3000, an appropriate code needs to be programmed. As the code takes a critical part to the measurement time, it needs to be taken into account carefully how the code will process the data acquired from the ADC and DAC so that it can be optimized and work efficiently. The combination of fast reading time and accurate graph-plotting will introduce a good result in getting the goals. Figure. 1. Working Diagram of Curve Tracer B.Requirements As seen on the diagram above, the curve tracer will have 3 main blocks: input voltage converter, output voltage converter, and plotting tools. These three diagrams are the main items of this project. According to the diagram, the construction of the project can be divided into 2 parts: hardware and software. The hardware part consists of input and voltage converter while the software composes of the plotting tools. Hardware Part Input voltage shifter o The input of this circuit comes from sweeping voltage or AC waveform o The voltage entering the DUT ranges from -10 to 10V or -5 to 5V o The input voltage must be shifted once again before entering the DUT Output voltage shifter o The input of this circuit comes from the measured diode voltage o The voltage leaving the DUT must be translated to 0-5V, to be able to recognize by the software part Both of the input and output shifter should be printed on one PCB. The hardware part should be compatible with the software part Software Part The graph should resemble the diode curve so that it can be comparable with it. The graph should consist of V-I (Voltage and Current) as the axis respectively Have to be user friendly, reusable, versatile, and robust. Easy to be maintained by other engineers. Clear documentation for users. Use C programming language Has to compatible with Altium Designer software C. Objectives The objectives of the assignment will be describes as below: The output graph will be presented on the NB3000 screen The graph should be able to represent the shape of a diode curve The curve tracer measurement time of a diode should be less than 4 seconds. The curve tracer components should have meet the requirement as mentioned in the sub chapter 3.2 The curve tracer should be able to do a consecutive measurement of several devices D. Description of Assignment The main assignment of this project is to create the hardware part and software part of the curve tracer. The hardware part will be implemented on a circuit board while the software part will be executed on the Altium Designer software. These are several steps to conduct a measurement on the curve tracer: A tool ( AC waveform generator or DC power supply ) will generated input voltage (Vinput) The voltage needs to be translated to meet the input voltage requirement, which is from -10 to 10V or -5 to 5V. The voltage will go through a diode, which will be a component to be measured in this project. The voltage across the diode will be measured and read by the ADC on the NB3000, but before it can enter the ADC, it will be translated again between 0-5 V The ADC (Altium NB3000) will read the voltage across the diode and will send the data to the NB3000 processor The NB3000 processor will process the data and plot a graph according to the read voltage The steps can be seen on the figure below: Therefore, according to the steps above, the assignment can be elaborated as below:

3 JURNAL TEKNIK POMITS Vol. 1, No. 1, (2013) Hardware Part Design a circuit to convert the input voltage before entering the diode and measured voltage after leaving the diode, which is divided into two parts: input voltage shifter and output voltage shifter, as mentioned previously. The output of this circuit should meet the requirements written on previous sub-chapter. This design later printed on the PCB, with all the components chose specifically to meet the requirements. Thus, the PCB layout needs to be made, along with choosing all the required components for the circuit. Software Part Write a program to utilize the ADC of the NB3000 to be able to read the measured voltage Make a formula on the program to convert the voltage value into current value Plot the V and I value into a graph which is displayed on the Altium NB3000 screen Plot the graph on the specific area of the screen, make sure the program create the X and Y axis first before plotting the graph Create a function which can save the data acquired from the measurement as a file which can be opened on a Windows computer. III. BACKGROUND MATERIAL This chapter will elaborate some important subjects prior to the project. Since the comprehension of the materials is needed to fully understand the project, a brief description about the materials will be explained in this chapter. A. Diode A diode is an electrical component which allows current to flow through in one direction with low resistance in it, while on the other direction it has high resistance [3]. A diode is usually made of silicon and germanium. It is mainly used as a rectifier, AM signal demodulator, or logic determiner. voltage is applied across it, the depletion region become thinner and will become less resistive. To allow sustained current trough the diode, the depletion region must be fully gone. This condition will happen if certain voltage is applied through the diode, which called the forward voltage. The typical forward voltage for a silicon diode is 0.7V. As seen on the figure 6, when the diode reaches 0.7V, the current will become very high. Diode Equation The diode equation, invented by William Bradford Shockley, explains the current and voltage characteristic of an ideal diode[4]. Id = Is (e qvd nkt 1) Where, Id = Diode current (Amps) Is = Saturation current (Amps) e = Euler Constant (~2.7) q = Charge of electron (1.6 x coulombs) Vd = Voltage across diode (Volts) n = non-ideality coefficient (typically 1) k = Boltzmann s constant (1.38 x ) T = Junction temperature (Kelvin) Assuming the non-ideality coefficient is one and the diode is used in the room temperature of 298 K, the following formula can be obtained: Id = Is (e Vd ) B. Altium Designer Altium Designer is an Electronic Design Automation (EDA) software package for printed circuit board, FPGA and embedded software design, and associated library and release management automation. 1 It consists of several features, such as board design, soft design, and data management. Within this project, the main used highlights of this software are schematic and PCB level design, embedded design, and C to Hardware design. The Altium Designer software is one of the mainly used software in the designing role in the NXP Semiconductors. The students from the previous year also mainly used the Altium Designer as a tool to finish their projects. C. Altium NanoBoard 3000 Altium NanoBoard 3000 is a FPGA-platform device which is manufactured by Altium. The NB3000 can also be used together with the Altium Designer software to develop, implement, and test a digital project of a soft system design. Figure 2. Diode Characteristic The Current-Voltage Characteristic The symbol of the diode is explained on the figure 6. There are two poles, anode and cathode. The anode corresponds to the positive poles, while the cathode conform the negative pole. When a reverse-biasing voltage is applied on the diode, it will expand the depletion region and resist any current to flow through it. On the other hand, if a forward-biasing There are several features available on the NB3000, such as, ADC and DAC port, Ethernet port, color TFT touch Screen, SD-Card reader, LED Switch, USB port, JTAG Adapter, stereo speakers and so on. The NB3000 provides a fixed user FPGA, which has three versions on the market: Xilinx, Altera, and Lattice, located on its motherboard.

4 JURNAL TEKNIK POMITS Vol. 1, No. 1, (2013) Although the board provides several interesting features, only some of the features will be adapt in this project. The ADC and DAC port along with the TFT Screen are the main component used in this project. Step 5: Employing switch to choose correct voltage at the output The communication between the NB3000 and the Altium Designer software running in the PC is interfaced with USB connection. IV. USING DC SWEEP AS AN INPUT OF CURVE TRACER Figure 3. Altium Nanoboard NB 3000 The second method will employ DC sweep as the input of the curve tracer. This method has been used on the previous project[5], but this time it is made with different requirements and some modifications. The previous project use the external DAC and ADC while in this project, internal DAC and ADC from the Altium NB3000 will be used. On the previous project, for calculating the current of the current of the diode, it used the Ohm s law formula with constant load resistance of 1.5 kohm as the resistor value. While on this project, the diode current will be measured through the voltage of the diode by using Shockley s equation. In this project the voltage input will be obtained from the DAC of Altium NB3000. Since the requirements of the input voltage of the diode will be between -10 and 10V, the voltage needs to be shifted first. The same goes for the measured voltage of the diode which needs to be between 0-5V to make it readable by the ADC[6]. A. Hardware Design Step Step 1: Shifting the DAC Voltage to make it range from negative voltage (-2.5 to 2.5 V)[7] Step 2: Amplify the voltage by 4 times [8] Step 3: Doing the measurement on the diode Step 4: Shifting the result of the measurement voltage back to positive value so the ADC can read it a. Shifting the negative voltage into positive voltage b. Shifting the positive voltage Figure 4. Hardware Design of DC Sweep Method B. Software Design Step Step 1: FPGA Design Part a. Create Open Bus b. Create FPGA Schematic Step 2: Embedded Software Design a. Establish Software Platform b. Create C-to-Hardware Programming C. Result Figure 5. Result on the Altium NB3000 Screen V. USING WAVEFORM AS AN INPUT OF THE CURVE TRACER To measure the semiconductor components, particularly

5 JURNAL TEKNIK POMITS Vol. 1, No. 1, (2013) diodes, an AC waveform is applied as an input to the curve tracer for obtaining faster measurement time. By different types of waveform, such as sine wave and saw tooth wave, with a frequency input that is compatible with the diode, the measuring time should be faster because we can define the sweeping time of the waveform - by setting its frequency and amplitude. Still, the diode used in this experiment is a low frequency diode. Then, it needs to be taken account that the frequency used should not exceed 1Khz. A. Hardware Design Step Step 1: Placing the Measured Diode Step 2: Shifting the Input Voltage from the Wave Generator Step 3: Shifting the voltage on the Y Axis Step 4: Measurement on Oscilloscope Step 5: Measurement with a Zener Diode Step 6: Measurement on the Altium NB3000 Figure 6. Hardware Design of Waveform method B. Software Design Step Step 1: FPGA Design Part c. Create Open Bus d. Create FPGA Schematic Step 2: Embedded Software Design c. Establish Software Platform d. Create C-to-Hardware Programming C. Result Figure 7. Result on the Altium NB3000 Screen VI. CONCLUSION & RECCOMENDATION A. CONCLUSION There are two methods which were conducted in this project. Both methods aim to fasten the measurement time of a curve tracer. After finishing both experiments, a faster method will be chosen as the initial input of the curve tracer. The first method, which using DC sweep as an input of the curve tracer, has already been applied last year. Still, the measurement time has not met the requirement from the company. Thus, an alteration of the method was brought in. The previous project employed external tools as an input of the curve tracer, such as its own ADC-DAC board and a DC power supply to sweep the voltage. While in this project, the ADC-DAC of the NB3000 will be utilized. By sweeping the input of the curve tracer with the DAC of the NB3000 and reading the measurement output with the NB3000 s ADC, it will fasten the measurement time. However, a definite time of the measurement cannot be determined. Since the printed board has not been delivered when the thesis is submitted, the measurement time of the curve tracer with this method cannot be evaluated. Another method employs an AC waveform as an input of the curve tracer. Choosing the frequency of waveform plays an important part for displaying the correct graph of a diode. Since a diode cannot hold the high frequency running through it, running high frequency would break the diode. By using saw tooth waveform which produces more symmetrical wave, the measurement give smoother graph result. Using an AC signal, in this case saw tooth wave, with frequency of 50 Hz, will speed up the measurement time significantly since it only takes 20ms to produce a complete wave. Adding the plotting time of the Altium NB3000, it should be able to produce the correct graph in less than 4 seconds. Thus, this method is proved to give more significant measurement time than the other method. As The ADC and DAC ports of Altium NB3000 cannot read any voltage outside the boundary of 0-5 Volts. Then, an analog circuit to convert the voltage is needed. To shift the voltage before and after the measurement, a separate board was built. This board will later connected to the NB3000 board via the header pin. This is the reason why the hardware part needed to be built in this project. The hardware part later will be joined with the software part. It is connected to the ADC port and the FPGA board which has already programmed will plot the graph on its screen. This solution has proved as an effective way to build a curve tracer which can produce less measurement time. B. RECOMMENDATION Improve the method of using waveforms as an input of the curve tracer Test other semiconductor components Create a logging system to maintain the data of measurement Placing an offset on the FPGA instead of placing resistor used in the circuit

6 JURNAL TEKNIK POMITS Vol. 1, No. 1, (2013) BIBLIOGRAPHY [1] NXP Semiconductors. [2] Altium. "Altium Designer FPGA, Software and Systen Developmetn Training." Altium Limited, [3] Boylestad, Robert L., and Louis Nashelsky. Electronic Devices and Circuit Theory (9th Edition). Prentice Hall, [4] Naidu, S. Mani. Engineering Physics. Pearson Education India, [5] Gong, Mengyi. "Curve Tracer." Nijmegen, [6] Kuhn, Kenneth A. "Diode Characteristics." 2009: [7] Qiao, Yixiao. "Source Measurement Unit Design in Curve Tracer." Nijmegen, [8] Mancini, Ron. "Op Amps for Everyone." Design Reference, August 2002.