High Performance Schottky Diode for Digital Applications Preliminary Technical Data 2:24 PM,06/05/98 HSMS-2700/ -2702 -270B/-270C Features •Ultra-low series resistance for higher current handling Package Lead Code Identification Description The HSMS-2700 series of Schottky diodes, commonly referred to as clipping/clamping diodes, are optimal for circuit and waveshape preservation applications with high speed switching. Ultra-low series resistance, Rs, makes them ideal for protecting sensitive circuit elements against higher current transients carried on data lines. With picosecond switching, the HSMS-270x can respond to noise spikes with rise times as fast as 1ns. Low capacitance minimizes waveshape loss that causes to signal degradation. (Top View) 3 •Picosecond switching 3 •Low capacitance 1 Applications: 2 1 2 0, B 2, C Single Series Pair Analog and digital designs requiring circuit protection or waveform cleanup with high speed switching. DC Electrical Specifications for HSMS-270x Test Conditions: TA=25°C, single diode. HSMS -2700 -270B -2702 -270C Package Marking Code[1] J0 J2 Lead Code 0 B 2 C Configuration Single Series Pair Package Maximum forward voltage, Minimum breakdown voltage, Typical capacitance, Typical series resistance, Maximum effective carrier lifetime, Vf [mV] Vbr [V] CT [pF] Rs [Ω ] τ [ps] 550[2] 15[3] 6.7[4] 0.65 100[5] SOT-23 SOT-323 (3-lead SC-70) SOT-23 SOT-323 (3-lead SC-70) Notes: 1. Package marking code is laser marked 2. If = 100 mA 3. Ir =100 µA 4. Vr=0; f=1 MHz 5. Measured with Karkauer method at 20 mA; guaranteed by design 1 Absolute Maximum Ratings Test Conditions: TA=25º C, single diode. Symbol Unit If mA If_peak A Pt mW Pinv Absolute Maximum [1] HSMS-2700/-2702 HSMS-270B/-270C Description DC Forward Current 350 750 Peak surge current (1µs pulse) 1.0 1.0 Total Power Dissipation 250 825 V Peak Inverse Voltage 15 15 Tj °C Junction Temperature 150 150 Tstg °C Storage Temperature -65 to 150 -65 to 150 [2] Thermal resistance, junction to lead 500 150 θJC °C/W Notes: 1. Operation in excess of any one of these conditions may result in permanent damage to the device 2. TA= 25°C; where TA is defined to be the temperature at the package pins where the conatact is made to the circuit board. Linear and Non-linear Model SPICE Parameters of the HSMS-270x 0.08 pF 2 nH Rs SPICE model 2 Parameter Unit Value BV CJ0 EG IBV IS N RS PB PT M V pF eV A A 25 6.7 0.55 10E-4 1.4E-7 1.04 0.65 0.6 2 0.5 Ω V Part Number Ordering Information Part Number Number of Devices HSMS-2700-BLK HSMS-2700-TR1 HSMS-2700-TR2 100 3,000 10,000 HSMS-2702-BLK HSMS-2702-TR1 HSMS-2702-TR2 100 3,000 10,000 HSMS-270B-BLK HSMS-270B-TR1 HSMS-270B-TR2 100 3,000 10,000 HSMS-270C-BLK HSMS-270C-TR1 HSMS-270C-TR2 100 3,000 10,000 Container Antistatic Bag 7” Reel 13” Reel Antistatic Bag 7” Reel 13” Reel Antistatic Bag 7” Reel 13” Reel Antistatic Bag 7” Reel 13” Reel 3 300 500 100 Data calculated from SPICE parameters. If - Forward Current (mA) If - Forward Current (mA) 100 10 25°C 1 75°C -25°C .1 Data calculated from SPICE parameters. 10 25°C 1 75°C .1 -25°C .01 .01 0.0 0.1 0.2 0.3 0.4 Vf - Forward Voltage (V) 0.5 0.6 Figure 1. Forward Current vs. Forward Voltage at Temperature for HSMS-2700 and HSMS-2702 160 0.0 160 Maximum safe junction temperature Tj - Junction Temperature (C) Tj - Junction Temperature (C) 100 75°C 80 60 25°C 40 0.3 0.4 0.5 Vf - Forward Voltage (V) 0.7 0.8 Data calculated from SPICE parameters. 120 100 75°C 80 60 25°C 40 -25°C 20 -25°C 20 0 0 0 50 100 150 200 250 If - Forward Current (mA) 300 350 Figure 3. Junction Temperature vs. Forward Current as a Function of Heat Sink Temperature for the HSMS-2700 and the HSMS-2702 0 6 5 4 3 2 1 0 5 10 Vr - Reverse Voltage (V) 15 150 300 450 If - Forward Current (mA) 600 750 Figure 4. Junction Temperature vs. Forward Current as a Function of Heat Sink Temperature fo the HSMS-270B and HSMS-270C 7 Ct - Total Capacitance (pF) 0.6 Maximum safe junction temperature 140 Data calculated from SPICE parameters. 0.2 Figure 2. Forward Current vs. Forward Voltage at Temperature for HSMS-270B and HSMS-270C 140 120 0.1 20 Figure 5. Total Capacitance vs. Reverse Voltage page 4 comparison to that of 0.6 V in p-n junction diodes. See Figure 6. Applications Information Schottky Diode Fundamentals The HSMS-270x series of clipping/clamping diodes are Schottky devices. A Schottky device is a rectifying, metal-semiconductor contact formed between a metal and an n-doped or a p-doped semiconductor. When a metal-semiconductor junction is formed, free electrons flow across the junction from the semiconductor and fill the freeenergy states in the metal. This flow of electrons creates a depletion or potential across the junction. The difference in energy levels between semiconductor and metal is called a Schottky barrier. P-doped, Schottky-barrier diodes excel at applications requiring ultra low turn-on voltage (such as zero-biased RF detectors). But their very low, breakdown-voltage and high series-resistance make them unsuitable for the clipping and clamping applications involving high forward currents and high reverse voltages. Therefore, this discussion will focus entirely on n-doped, Schottky diodes. Under a forward bias (metal connected to positive in an n-doped Schottky) or forward voltage, Vf, there are many electrons with enough thermal energy to cross the barrier potential into the metal. Once the applied bias exceeds the built-in potential of the junction, the forward current, If, will increase rapidly as Vf increases. When the Schottky diode is reversed biased, the potential barrier for electrons becomes large; hence, there is a small probability that an electron will have sufficient thermal energy to cross the junction. The reverse leakage current will be in the nanoampere to microampere range, depending upon the diode type, the reverse voltage, and the temperature. U Figure 6. Comparison, P-N Junction to Schottky Diode Through the careful manipulation of the diameter of the Schottky contact and the choice of metal deposited on the n-doped silicon, the important characteristics of the diode (junction capacitance, Cj; parasitic series resistance, Rs; breakdown voltage, Vbr; and forward voltage, Vf) can be optimized for specific applications. The HSMS-270x series and HBAT-540x series of diodes are a case in point. Both diodes have similar barrier heights; and this is indicated by corresponding values of saturation current, Is. Yet, different contact diameters and epitaxial-layer thickness result in very different values of CJ and Rs. This is seen by comparing their SPICE parameters in Table 1. Parameters Symbol BV CJ0 EG IBV IS N RS PB PT M In contrast to a conventional p-n junction, the current in the Schottky diode is carried only by majority carriers (electrons). Because no minoritycarrier (hole), charge storage effects are present, Schottky diodes have carrier lifetimes of less than 100 ps. This extremely fast switching time makes the Schottky diode an ideal rectifier at frequencies of 50 GHz and higher. Another significant difference between Schottky and p-n diodes is the forward voltage drop. Schottky diodes have a threshold of typically 0.3 V in Unit V pF eV A A Ω V HSMS270x HSMS540x 25 40 6.7 3.0 0.55 10E-4 1.4E-7 1.04 0.55 10E-4 1.0E-7 1.0 0.65 2.4 0.6 2 0.5 0.6 2 0.5 Table 1. HSMS-270x and HBAT-540x SPICE Parameters page 5 At low values of If (values of 1 mA or less), the forward voltages of the two diodes are nearly identical. However, as current rises above 10 mA, the lower series resistance of the HSMS-270x allows for a much lower forward voltage. This gives the HSMS-270x a much higher current handling capability. The tradeoff is a higher value of junction capacitance. The forward voltage and current plots illustrate the differences in these two Schottky diodes, as shown in Figure 7. noisy data - spikes current limiting long cross-site cable pull-down (or pull-up) 300 HSMS-270x Data calculated from SPICE parameters. 0V voltage limited to: Vs + Vd 0V - Vd HBAT-540x Figure 8. Two Schottky diodes are used for clipping/clamping in a circuit. 10 Consider the circuit shown in Figure 8, in which two Schottky diodes are used to protect a circuit from noise spikes on a stream of digital data. The ability of the diodes to limit the voltage spikes is related to their ability to sink the associated current spikes. The importance of current handling capacity is shown in Figure 9, where the forward voltage generated by a forward current is compared in two diodes. 1 .1 .01 0.0 0.1 0.2 0.3 0.4 Vf - Forward Voltage (V) 0.5 0.6 Figure 7. Forward Current vs. Forward Voltage at 25°C Because the automatic, pick-and-place equipment used to assemble these products selects dice from adjacent sites on the wafer, the two diodes which go into the HSMS-2702 or HSMS-270C (series pair) are closely matched— without the added expense of testing and binning. Current handling in clipping/clamping circuits The purpose of a clipping/clamping diode is to handle high currents, protecting delicate circuits downstream of the diode. Current handling capacity is determined by two sets of characteristics, those of the chip or device itself and those of the package into which it is mounted. 6 5 Vf - Forward voltage (V) If - Forward Current (mA) 100 Vs 4 Rs = 7.7Ω 3 2 Rs = 1.0Ω 1 0 0.0 0.1 0.2 0.3 If - Forward current (mA) Figure 9. Comparison of two diodes 0.4 0.5 V-I.ATB The first is a conventional Schottky diode of the type generally used in RF circuits, with an Rs of 7.7 Ω. The second is a Schottky diode of identical characteristics, save the Rs of 1.0 Ω. For the conventional diode, the relatively high value of Rs causes the voltage across the diode's terminals to rise as current increases. The power dissipated in the diode heats the junction, causing Rs to climb, giving rise to a runaway thermal condition. In the page 6 second diode with low Rs, such heating does not take place and the voltage across the diode terminals is maintained at a low limit even at high values of current. Maximum reliability is obtained in a Schottky diode when the steady state junction temperature is maintained at or below 150°C, although brief excursions to higher junction temperatures can be tolerated with no significant impact upon meantime-to-failure, MTTF. In order to compute the junction temperature, Equations (1) and (3) below must be simultaneously solved. 11600 V f If Rs n Tj If I s e 2 Is I0 Tj 298 4060 n e Tj = Vf I f θjc + T a 1 1 1 Tj 298 (1) (2) (3) where: If = forward current Is = saturation current Vf = forward voltage Rs = series resistance Tj = junction temperature I0 = saturation current at 25°C n = diode ideality factor θjc = thermal resistance from junction to case (diode lead) = θpackage + θchip Ta = ambient (diode lead) temperature chip thermal resistance of the Schottky die; and θpackage, or the package thermal resistance. Rs for the HSMS-270x family of diodes is typically 0.7 Ω and the lowest of any Schottky diode available from Hewlett-Packard (H-P). Chip thermal resistance is typically 40°C/W; the thermal resistance of the iron-alloy-leadframe, SOT-23 package is typically 460°C/W; and the thermal resistance of the copper-leadframe, SOT-323 package is typically 110°C/W. The impact of package thermal resistance on the current handling capability of these diodes can be seen in Figures 3 and 4. Here the computed values of junction temperature vs. forward current are shown for three values of ambient temperature. The SOT-323 products, with their copper leadframes, can safely handle almost twice the current of the larger SOT-23 diodes. Note that the term "ambient temperature" refers to the temperature of the diode's leads, not the air around the circuit board. It can be seen that the HSMS-270B and HSMS-270C products in the SOT-323 package will safely withstand a steadystate forward current of 550 mA when the diode's terminals are maintained at 75°C. For pulsed currents and transient current spikes of less than one microsecond in duration, the junction does not have time to reach thermal steady state. Moreover, the diode junction may be taken to temperatures higher than 150°C for short timeperiods without impacting device MTTF. Because of these factors, higher currents can be safely handled. The HSMS-270x family has the highest current handling capability of any H-P diode. Equation (1) describes the forward V-I curve of a Schottky diode. Equation (2) provides the value for the diode's saturation current, which value is plugged into (1). Equation (3) gives the value of junction temperature as a function of power dissipated in the diode and ambient (lead) temperature. The key factors in these equations are: Rs, the series resistance of the diode where heat is generated under high current conditions; θchip, the page 7