Surface Mount Zero Bias Schottky Detector Diodes Technical Data HSMS-2850 Series Features * Surface Mount SOT-23/ SOT-143 Packages SOT-23/SOT-143 Package Lead Code Identification (top view) * Miniature SOT-323 and SOT-363 Packages SINGLE 3 SERIES 3 1 1 * High Detection Sensitivity: up to 50 mV/W at 915 MHz * Low Flicker Noise: -162 dBV/Hz at 100 Hz 2 #0 UNCONNECTED PAIR 3 4 * Low FIT (Failure in Time) Rate* * Tape and Reel Options Available 1 * Matched Diodes for Consistent Performance * Better Thermal Conductivity for Higher Power Dissipation Pin Connections and Package Marking 3 PLx 2 6 5 4 Notes: 1. Package marking provides orientation and identification. 2. See "Electrical Specifications" for appropriate package marking. #5 2 SOT-323 Package Lead Code Identification (top view) * For more information see the Surface Mount Schottky Reliability Data Sheet. 1 2 #2 SINGLE 3 SERIES 3 1 1 B 2 C 2 SOT-363 Package Lead Code Identification (top view) BRIDGE QUAD UNCONNECTED TRIO 6 5 1 2 L 4 6 5 3 1 2 4 P 3 Description Agilent's HSMS-285x family of zero bias Schottky detector diodes has been designed and optimized for use in small signal (Pin < -20 dBm) applications at frequencies below 1.5 GHz. They are ideal for RF/ID and RF Tag applications where primary (DC bias) power is not available. Important Note: For detector applications with input power levels greater than -20 dBm, use the HSMS-282x series at frequencies below 4.0 GHz, and the HSMS-286x series at frequencies above 4.0 GHz. The HSMS-285x series IS NOT RECOMMENDED for these higher power level applications. Available in various package configurations, these detector diodes provide low cost solutions to a wide variety of design problems. Agilent's manufacturing techniques assure that when two diodes are mounted into a single package, they are taken from adjacent sites on the wafer, assuring the highest possible degree of match. 2 SOT-23/SOT-143 DC Electrical Specifications, TC = +25C, Single Diode Part Number HSMS- Package Marking Code[1] Lead Code Configuration 2850 2852 2855 P0 P2 P5 0 2 5 Single Series Pair [2,3] Unconnected Pair [2,3] Test Conditions Maximum Forward Voltage VF (mV) 150 Typical Capacitance CT (pF) 250 0.30 IF = 0.1 mA IF = 1.0 mA VR = -0.5 V to -1.0V f = 1 MHz Notes: 1. Package marking code is in white. 2. VF for diodes in pairs is 15.0 mV maximum at 1.0 mA. 3. CT for diodes in pairs is 0.05 pF maximum at -0.5 V. SOT-323/SOT-363 DC Electrical Specifications, TC = +25C, Single Diode Part Number HSMS- Package Marking Code[1] Lead Code 285B 285C 285L 285P P0 P2 PL PP B C L P Configuration Single [2] Series Pair [2,3] Unconnected Trio Bridge Quad Test Conditions Maximum Forward Voltage VF (mV) 150 250 IF = 0.1 mA IF = 1.0 mA Typical Capacitance CT (pF) 0.30 VR = 0.5 V to -1.0V f = 1 MHz Notes: 1. Package marking code is laser marked. 2. VF for diodes in pairs is 15.0 mV maximum at 1.0 mA. 3. CT for diodes in pairs is 0.05 pF maximum at -0.5 V. RF Electrical Specifications, TC = +25C, Single Diode Part Number HSMS- Typical Tangential Sensitivity TSS (dBm) @ f = 915 MHz Typical Voltage Sensitivity Typical Video (mV/ W) @ f = 915 MHz Resistance RV (K) 2850 2852 2855 285B 285C 285L 285P -57 40 8.0 Test Conditions Video Bandwidth = 2 MHz Zero Bias Power in = -40 dBm RL = 100 K, Zero Bias Zero Bias 3 Absolute Maximum Ratings, TC = +25C, Single Diode Symbol Parameter Unit Absolute Maximum[1] SOT-23/143 SOT-323/363 PIV Peak Inverse Voltage V 2.0 2.0 TJ Junction Temperature C 150 150 TSTG Storage Temperature C -65 to 150 -65 to 150 TOP Operating Temperature C -65 to 150 -65 to 150 C/W 500 150 jc Thermal Resistance[2] ESD WARNING: Handling Precautions Should Be Taken To Avoid Static Discharge. Notes: 1. Operation in excess of any one of these conditions may result in permanent damage to the device. 2. TC = +25C, where TC is defined to be the temperature at the package pins where contact is made to the circuit board. Equivalent Linear Circuit Model HSMS-285x chip Rj RS Cj RS = series resistance (see Table of SPICE parameters) C j = junction capacitance (see Table of SPICE parameters) Rj = 8.33 X 10-5 nT Ib + Is where Ib = externally applied bias current in amps Is = saturation current (see table of SPICE parameters) T = temperature, K n = ideality factor (see table of SPICE parameters) Note: To effectively model the packaged HSMS-285x product, please refer to Application Note AN1124. SPICE Parameters Parameter Units HSMS-285x BV V 3.8 CJ0 pF 0.18 EG eV 0.69 I BV A 3 E -4 IS A 3 E-6 N 1.06 RS 25 PB (VJ) V 0.35 PT (XTI) 2 M 0.5 4 Typical Parameters, Single Diode 10000 RL = 100 K 1000 1 0.1 915 MHz VOLTAGE OUT (mV) 10 100 10 1 10 915 MHz 1 DIODES TESTED IN FIXED-TUNED FR4 MICROSTRIP CIRCUITS. 0.01 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 VF - FORWARD VOLTAGE (V) Figure 1. Typical Forward Current vs. Forward Voltage. 3.1 2.9 OUTPUT VOLTAGE (mV) 30 RL = 100 K VOLTAGE OUT (mV) IF - FORWARD CURRENT (mA) 100 2.7 FREQUENCY = 2.45 GHz PIN = -40 dBm RL = 100 K 2.5 2.3 2.1 1.9 1.7 1.5 1.3 MEASUREMENTS MADE USING A 1.1 FR4 MICROSTRIP CIRCUIT. 0.9 0 10 20 30 40 50 60 70 80 90 100 TEMPERATURE (C) Figure 4. Output Voltage vs. Temperature. 0.1 -50 -40 -30 -20 -10 0 POWER IN (dBm) Figure 2. +25C Output Voltage vs. Input Power at Zero Bias. 0.3 -50 DIODES TESTED IN FIXED-TUNED FR4 MICROSTRIP CIRCUITS. -40 -30 POWER IN (dBm) Figure 3. +25C Expanded Output Voltage vs. Input Power. See Figure 2. 5 Applications Information Introduction Agilent's HSMS-285x family of Schottky detector diodes has been developed specifically for low cost, high volume designs in small signal (Pin < -20 dBm) applications at frequencies below 1.5 GHz. At higher frequencies, the DC biased HSMS-286x family should be considered. In large signal power or gain control applications (Pin > -20 dBm), the HSMS-282x and HSMS-286x products should be used. The HSMS-285x zero bias diode is not designed for large signal designs. Schottky Barrier Diode Characteristics Stripped of its package, a Schottky barrier diode chip consists of a metal-semiconductor barrier formed by deposition of a metal layer on a semiconductor. The most common of several different types, the passivated diode, is shown in Figure 5, along with its equivalent circuit. RS METAL PASSIVATION N-TYPE OR P-TYPE EPI PASSIVATION LAYER SCHOTTKY JUNCTION Cj Rj tance of the diode, controlled by the thickness of the epitaxial layer and the diameter of the Schottky contact. R j is the junction resistance of the diode, a function of the total current flowing through it. 8.33 X 10-5 n T R j = ------------ = R V - R s IS + I b 0.026 = ----- at 25C IS + I b where n = ideality factor (see table of SPICE parameters) T = temperature in K IS = saturation current (see table of SPICE parameters) Ib = externally applied bias current in amps IS is a function of diode barrier height, and can range from picoamps for high barrier diodes to as much as 5 A for very low barrier diodes. The Height of the Schottky Barrier The current-voltage characteristic of a Schottky barrier diode at room temperature is described by the following equation: Through the choice of p-type or n-type silicon, and the selection of metal, one can tailor the characteristics of a Schottky diode. Barrier height will be altered, and at the same time CJ and RS will be changed. In general, very low barrier height diodes (with high values of IS, suitable for zero bias applications) are realized on p-type silicon. Such diodes suffer from higher values of RS than do the n-type. Thus, p-type diodes are generally reserved for small signal detector applications (where very high values of RV swamp out high RS) and n-type diodes are used for mixer applications (where high L.O. drive levels keep RV low). Measuring Diode Parameters The measurement of the five elements which make up the low frequency equivalent circuit for a packaged Schottky diode (see Figure 6) is a complex task. Various techniques are used for each element. The task begins with the elements of the diode chip itself. CP V - IR I = IS (exp ------S - 1) 0.026 ( ) LP N-TYPE OR P-TYPE SILICON SUBSTRATE CROSS-SECTION OF SCHOTTKY BARRIER DIODE CHIP current, IS, and is related to the barrier height of the diode. EQUIVALENT CIRCUIT Figure 5. Schottky Diode Chip. RS is the parasitic series resistance of the diode, the sum of the bondwire and leadframe resistance, the resistance of the bulk layer of silicon, etc. RF energy coupled into RS is lost as heat -- it does not contribute to the rectified output of the diode. CJ is parasitic junction capaci- On a semi-log plot (as shown in the Agilent catalog) the current graph will be a straight line with inverse slope 2.3 X 0.026 = 0.060 volts per cycle (until the effect of RS is seen in a curve that droops at high current). All Schottky diode curves have the same slope, but not necessarily the same value of current for a given voltage. This is determined by the saturation RV RS Cj FOR THE HSMS-285x SERIES CP = 0.08 pF LP = 2 nH Cj = 0.18 pF RS = 25 RV = 9 K Figure 6. Equivalent Circuit of a Schottky Diode. 6 RS is perhaps the easiest to measure accurately. The V-I curve is measured for the diode under forward bias, and the slope of the curve is taken at some relatively high value of current (such as 5 mA). This slope is converted into a resistance Rd. 0.026 RS = Rd - ------ If RV and CJ are very difficult to measure. Consider the impedance of CJ = 0.16 pF when measured at 1 MHz -- it is approximately 1 M. For a well designed zero bias Schottky, RV is in the range of 5 to 25 K, and it shorts out the junction capacitance. Moving up to a higher frequency enables the measurement of the capacitance, but it then shorts out the video resistance. The best measurement technique is to mount the diode in series in a 50 microstrip test circuit and measure its insertion loss at low power levels (around -20 dBm) using an HP8753C network analyzer. The resulting display will appear as shown in Figure 7. -10 50 INSERTION LOSS (dB) -15 sets the loss, which plots out as a straight line when frequency is plotted on a log scale. Again, calculation is straightforward. LP and CP are best measured on the HP8753C, with the diode terminating a 50 line on the input port. The resulting tabulation of S11 can be put into a microwave linear analysis program having the five element equivalent circuit with RV, CJ and RS fixed. The optimizer can then adjust the values of LP and CP until the calculated S11 matches the measured values. Note that extreme care must be taken to de-embed the parasitics of the 50 test fixture. Detector Circuits When DC bias is available, Schottky diode detector circuits can be used to create low cost RF and microwave receivers with a sensitivity of -55 dBm to -57 dBm.[1] These circuits can take a variety of forms, but in the most simple case they appear as shown in Figure 8. This is the basic detector circuit used with the HSMS-285x family of diodes. 0.16 pF 50 -20 -25 In the design of such detector circuits, the starting point is the equivalent circuit of the diode, as shown in Figure 6. 50 9 K -30 50 -35 -40 3 10 100 1000 3000 FREQUENCY (MHz) Figure 7. Measuring CJ and RV. At frequencies below 10 MHz, the video resistance dominates the loss and can easily be calculated from it. At frequencies above 300 MHz, the junction capacitance Of interest in the design of the video portion of the circuit is the diode's video impedance -- the other four elements of the equivalent circuit disappear at all reasonable video frequencies. In general, the lower the diode's video impedance, the better the design. [1] [2] RF IN Z-MATCH NETWORK RF IN Z-MATCH NETWORK VIDEO OUT VIDEO OUT Figure 8. Basic Detector Circuits. The situation is somewhat more complicated in the design of the RF impedance matching network, which includes the package inductance and capacitance (which can be tuned out), the series resistance, the junction capacitance and the video resistance. Of these five elements of the diode's equivalent circuit, the four parasitics are constants and the video resistance is a function of the current flowing through the diode. 26,000 RV ------ I S + Ib where IS = diode saturation current in A Ib = bias current in A Saturation current is a function of the diode's design,[2] and it is a constant at a given temperature. For the HSMS-285x series, it is typically 3 to 5 A at 25C. Saturation current sets the detection sensitivity, video resistance and input RF impedance of the zero bias Schottky detector diode. Agilent Application Note 923, Schottky Barrier Diode Video Detectors. Agilent Application Note 969, An Optimum Zero Bias Schottky Detector Diode. 7 The most difficult part of the design of a detector circuit is the input impedance matching network. For very broadband detectors, a shunt 60 resistor will give good input match, but at the expense of detection sensitivity. When maximum sensitivity is required over a narrow band of frequencies, a reactive matching network is optimum. Such networks can be realized in either lumped or distributed elements, depending upon frequency, size constraints and cost limitations, but certain general design principals exist for all types.[3] Design work begins with the RF impedance of the HSMS-285x series, which is given in Figure 9. 2 0.2 0.6 0 65nH RF INPUT VIDEO OUT WIDTH = 0.050" LENGTH = 0.065" 100 pF WIDTH = 0.015" LENGTH = 0.600" TRANSMISSION LINE DIMENSIONS ARE FOR MICROSTRIP ON 0.032" THICK FR-4. Figure 10. 915 MHz Matching Network for the HSMS-285x Series at Zero Bias. A 65 nH inductor rotates the impedance of the diode to a point on the Smith Chart where a shunt inductor can pull it up to the center. The short length of 0.065" wide microstrip line is used to mount the lead of the diode's SOT-323 package. A shorted shunt stub of length