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surface mount rf schottky detector diodes in sot-363 (sc-70, 6 lead) technical data features ? surface mount sot-363 package ? high detection sensitivity: up to 50 mv/ m w at 915 mhz up to 35 mv/ m w at 2.45 ghz up to 25 mv/ m w at 5.80 ghz ? low flicker noise: -162 dbv/hz at 100 hz ? low fit (failure in time) rate* ? tape and reel options available * for more information see the surface mount schottky reliability data sheet. hsms-285l/p hsms-286l/p/r package lead code identification (top view) description hewlett-packards hsms-285l/p family of zero bias schottky detector diodes and the hsms-286 l/p/r family of dc biased detector diodes have been designed and optimized for use from 915 mhz to 5.8 ghz. they are ideal for rf/id and rf tag, cellular and other consumer applica- tions requiring small and large signal detection, modulation, rf to dc conversion or voltage doubling. available in various package configurations, these two families of detector diodes provide low cost solutions to a wide variety of design problems. hewlett-packards manufacturing techniques assure that when multiple diodes are mounted into a single sot-363 package, they are taken from adjacent sites on the wafer, assuring the highest possible degree of match. bridge quad p unconnected trio l ring quad r 123 654 123 654 123 654 dc electrical specifications, t c = +25 c, single diode part package maximum forward typical number marking lead voltage v f capacitance c t hsms- code [1] code configuration (mv) (pf) 285l pl l unconnected trio 150 250 0.30 285p pp p bridge quad 286l tl l unconnected trio 250 350 0.25 286p tp p bridge quad 286r zz r ring quad test conditions i f = 0.1 ma [2] i f = 1.0 ma [2] v r = 0.5 v to -1.0 v f = 1 mhz [3] notes: 1. package marking code is laser marked. 2. d v f for diodes in trios and quads is 15.0 mv maximum at 1.0 ma. 3. d c t for diodes in trios and quads is 0.05 pf maximum at -0.5 v.
2 rf electrical parameters, t c = +25 o c, single diode part typical tangential sensitivity typical voltage sensitivity g typical video number tss (dbm) @ f = (mv/ m w) @ f = resistance r v (k w ) hsms- 915 mhz 2.45 ghz 5.8 ghz 915 mhz 2.45 ghz 5.8 ghz 285l -57 -56 -55 40 30 22 8.0 285p test video bandwidth = 2 mhz power in = -40 dbm conditions zero bias r l = 100 k w , zero bias 286l -57 -56 -55 50 35 25 5.0 286p 286r test video bandwidth = 2 mhz power in = C 40 dbm conditions i b = 5 m ar l = 100 k w , i b = 5 m a symbol parameter unit absolute maximum [1] p iv peak inverse voltage v 2.0 t j junction temperature c 150 t stg storage temperature c -65 to 150 t op operating temperature c -65 to 150 q jc thermal resistance [2] c/w 140 notes: 1. operation in excess of any one of these conditions may result in permanent damage to the device. 2. t c = +25 c, where t c is defined to be the temperature at the pack- age pins where contact is made to the circuit board. esd warning: handling precautions should be taken to avoid static discharge. absolute maximum ratings, t c = 25oc, single diode equivalent circuit model hsms-285a series, hsms-286a series single diode spice parameters parameter units hsms-285a hsms-286a b v v 3.8 7.0 c jo pf 0.18 0.18 e g ev 0.69 0.69 i bv a 3 x 10e - 4 10e - 5 i s a 3 x 10e - 6 5 x 10e - 8 n 1.06 1.08 r s w 25 5.0 p b (v j ) v 0.35 0.65 p t (xti) 2 2 m 0.5 0.5 0.18 pf r j r s 0.08 pf 2 nh r j = 8.33 x 10 -5 nt i b + i s where i b = externally applied bias current in amps i s = saturation current (see table of spice parameters) t = temperature, k n = identity factor (see table of spice parameters) r s = series resistance (see table of spice parameters)
3 typical parameters, single diode 1 10 100 1 10 forward current ( a) forward voltage difference (mv) voltage out (mv) power in (dbm) 0.05 0.15 0.20 0.10 0.25 forward voltage (v) figure 3. forward voltage match, hsms-286a series. .01 .1 1 10 100 0.1 0.2 0.3 0.4 0.7 0.6 0.8 0.9 0.5 1.0 forward current (ma) forward voltage (v) figure 2. forward current vs. forward voltage at temperature, hsms-286a series. figure 1. +25 c forward current vs. forward voltage, hsms-285a series. 1 10 100 1000 10,000 ?0 ?0 ?0 0 ?0 10 figure 6. dynamic transfer characteristic as a function of dc bias, hsms-286a. figure 4. +25 c output voltage vs. input power, hsms-285a series at zero bias, hsms-286a series at 3 a bias. figure 5. +25 c expanded output voltage vs. input power. see figure 4. 5 35 30 40 10 15 20 25 .1 1 10 100 output voltage (mv) bias current ( a) figure 7. voltage sensitivity as a function of dc bias current, hsms-286a. figure 8. output voltage vs. temperature, hsms-285a series. t a = +85 c t a = +25 c t a = ?5 c i f (left scale) ? v f (right scale) frequency = 2.45 ghz fixed-tuned fr4 circuit r l = 100 k 20 a 5 a 10 a input power = ?0 dbm @ 2.45 ghz data taken in fixed-tuned fr4 circuit r l = 100 k i f ?forward current (ma) 0 0.01 v f ?forward voltage (v) 0.8 1.0 100 1 0.1 0.2 1.8 10 1.4 0.4 0.6 1.2 1.6 voltage out (mv) -50 0.3 power in (dbm) -30 -20 10000 10 1 -40 0 100 -10 1000 r l = 100 k w 5.8 ghz diodes tested in fixed-tuned fr4 microstrip circuits. 915 mhz 2.45 ghz voltage out (mv) -50 0.3 power in (dbm) -30 10 1 -40 30 r l = 100 k w 2.45 ghz 915 mhz 5.8 ghz diodes tested in fixed-tuned fr4 microstrip circuits. output voltage (mv) 0 0.9 temperature ( c) 40 50 3.1 2.1 1.5 10 100 2.5 80 20 30 70 90 60 1.1 1.3 1.7 1.9 2.3 2.7 2.9 measurements made using a fr4 microstrip circuit. frequency = 2.45 ghz p in = -40 dbm r l = 100 k w
4 applications information introduction hewlett-packards hsms-285l and hsms-285p zero bias schottky diodes have been developed specifically for low cost, high volume detector applications where bias current is not available. the hsms-286l, hsms-286p and hsms-286r dc biased schottky diodes have been developed for low cost, high volume detector applications where stability over temperature is an important design consideration. 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 9, along with its equivalent circuit. figure 9. schottky diode chip. r s 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 r s is lost as heat it does not contribute to the rectified output of the diode. c j is parasitic junction capacitance 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 nt r j = CCCCCCCCCCCC = r v C r s i s + i b 0.026 = CCCCC at 25 c i s + i b where n = ideality factor (see table of spice parameters) t = temperature in k i s = saturation current (see table of spice parameters) i b = externally applied bias current in amps i s is a function of diode barrier height, and can range from picoamps for high barrier diodes to as much as 5 m 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: v C ir s i = i s (e ( CCCCCCC ) C 1) 0.026 on a semi-log plot (as shown in the hp 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 r s 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 current, i s , and is related to the barrier height of the diode. 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 c j and r s will be changed. in general, very low barrier height diodes (with high values of i s , suitable for zero bias applications) are realized on p-type silicon. such diodes suffer from higher values of r s than do the n-type. thus, p-type diodes are generally reserved for detector applications (where very high values of r v swamp out high r s ) and n-type diodes are used for mixer applications (where high l.o. drive levels keep r v low). measuring diode linear parameters the measurement of the five elements which make up the equivalent circuit for a packaged schottky diode (see figure 10) is a complex task. various techniques are used for each element. the task begins with the elements of the diode chip itself. l p r s r v c j c p for the hsms-285a or hsms-286a series c p = 0.08 pf l p = 2 nh c j = 0.18 pf r s = 25 w r v = 9 k w figure 10. equivalent circuit of a schottky diode. r s 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 r d . 0.026 r s = r d C CCCCCC i f r s r j c j metal schottky junction passivation passivation n-type or p-type epi layer n-type or p-type silicon substrate cross-section of schottky barrier diode chip equivalent circuit
5 r v and c j are very difficult to measure. consider the impedance of c j = 0.16 pf when measured at 1 mhz it is approximately 1 m w . for a well designed zero bias schottky, r v is in the range of 5 to 25 k w , 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 w 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 11. insertion loss (db) 3 -40 frequency (mhz) -10 -25 3000 -20 10 1000 100 -35 -30 -15 50 w 50 w 0.16 pf 50 w 50 w 9 k w figure 11. measuring c j and r v . 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 sets the loss, which plots out as a straight line when frequency is plotted on a log scale. again, calculation is straightforward. l p and c p are best measured on the hp8753c, with the diode terminating a 50 w line on the input port. the resulting tabulation of s 11 can be put into a microwave linear analysis program having the five element equivalent circuit with r v , c j and r s fixed. the optimizer can then adjust the values of l p and c p until the calculated s 11 matches the measured values. note that extreme care must be taken to de- embed the parasitics of the 50 w 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] moreover, since external dc bias sets the video impedance of such circuits, they display classic square law response over a wide range of input power levels [2,3] . these circuits can take a variety of forms, but in the most simple case they appear as shown in figure 12. this is the basic detector circuit used with the hsms-286x family of diodes. where dc bias is not available, a zero bias schottky diode is used to replace the conventional schottky in these circuits, and bias choke l 1 is eliminated. the circuit then is reduced to a diode, an rf impedance matching network and (if required) a dc return choke and a capacitor. this is the basic detector circuit used with the hsms-285a family of diodes. output voltage can be virtually doubled and input impedance (normally very high) can be halved through the use of the voltage doubler circuit [4] . in the design of such detector circuits, the starting point is the equivalent circuit of the diode, as shown in figure 10. of interest in the design of the video portion of the circuit is the diodes video impedance the other four elements of the equivalent circuit disappear at all reasonable video frequencies. in general, the lower the diodes video impedance, the better the design. video out rf in z-match network l 1 dc bias video out z-match network l 1 dc bias rf in figure 12. 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 [1] hewlett-packard application note 923, schottky barrier diode video detectors. [2] hewlett-packard application note 986, square law and linear detection. [3] hewlett-packard application note 956-5, dynamic range extension of schottky detectors. [4] hewlett-packard application note 956-4, schottky diode voltage doubler.
6 capacitance and the video resistance. of these five elements of the diodes equivalent circuit, the four parasitics are constants and the video resistance is a function of the current flowing through the diode. 26,000 r v ? CCCCCC i s + i b where i s = diode saturation current in m a i b = bias current in m a saturation current is a function of the diodes design, [5] and it is a constant at a given temperature. for the hsms-285x series, it is typically 3 to 5 m a at 25 c. for the medium barrier hsms-2860 family, saturation current at room temperature is on the order of 50 na. together, saturation and (if used) bias current set the detection sensitivity, video resistance and input rf impedance of the schottky detector diode. since no external bias is used with the hsms-285a series, a single transfer curve at any given frequency is obtained, as shown in figure 4. where bias current is used, some tradeoff in sensitivity and square law dynamic range is seen, as shown in figure 6 and described in reference [3]. the most difficult part of the design of a detector circuit is the input impedance matching network. a discussion of such circuits can be found in the data sheet for the hsms-285a/hsms- 286a single sot-323 detector diodes (hewlett-packard publication 5965-4704e). six lead circuits the differential detector is often used to provide temperature compensation for a schottky detector, as shown in figure 13. matching network differential amplifier bias figure 13. voltage doubler. these circuits depend upon the use of two diodes having matched v f characteristics over all operat- ing temperatures. this is best achieved by using two diodes in a single package, such as the hsms-2825 in the larger sot-143 package. however, such circuits generally use single diode detec- tors, either series or shunt mounted diode. the voltage doubler (reference [4]) offers the advantage of twice the output voltage for a given input power. the two concepts can be com- bined into the differential voltage doubler, as shown in figure 14. matching network bias differential amplifier figure 14. differential voltage doubler. here, all four diodes of the hsms-286p are matched in their v f characteristics, because they came from adjacent sites on the wafer. a similar circuit can be realized using the hsms-286r ring quad. other configurations of six lead schottky products can be used to solve circuit design problems while saving space and cost. thermal considerations the obvious advantage of the sot-363 over the sot-143 is combination of smaller size and two extra leads. however, the copper leadframe in the sot-363 has a thermal conductivity four times higher than the alloy 42 leadframe of the sot-143, which enables it to dissipate more power. the maximum junction tempera- ture for these three families of schottky diodes is 150 c under all operating conditions. the follow- ing equation, equation 1, applies to the thermal analysis of diodes: t j = (v f i f + p rf ) q jc + t a where t j = junction temperature t a = diode case temperature q jc = thermal resistance v f i f = dc power dissipated p rf = rf power dissipated equation (1). note that q jc , the thermal resis- tance from diode junction to the foot of the leads, is the sum of two component resistances, q jc = q pkg + q chip equation (2). [5] hewlett-packard application note 969, an optimum zero bias schottky detector diode.
7 package thermal resistance for the sot-363 package is approxi- mately 100 c/w, and the chip thermal resistance for these three families of diodes is approxi- mately 40 c/w. the designer will have to add in the thermal resistance from diode case to ambient a poor choice of circuit board material or heat sink design can make this number very high. equation (1) would be straightfor- ward to solve but for the fact that diode forward voltage is a func- tion of temperature as well as forward current. the equation, equation 3, for v f is: 11600 (v f C i f r s ) nt i f = i s e C 1 where n = ideality factor t = temperature in k r s = diode series resistance equation (3). and i s (diode saturation current) is given by 2 1 1 n C 4060 ( t C 298 ) i s = i 0 ( t ) e 298 equation (4). equations (1) and (3) are solved simultaneously to obtain the value of junction temperature for given values of diode case temperature, dc power dissipation and rf power dissipation. temperature compensation the compression of the detectors transfer curve is beyond the scope of this data sheet, but some general comments can be made. as was given earlier, the diodes video resistance is given by 8.33 x 10 -5 nt r v = CCCCCCCCCCCC i s + i b where t is the diodes tempera- ture in k. as can be seen, temperature has a strong effect upon r v , and this will in turn affect video bandwidth and input rf impedance. a glance at figure 7 suggests that the proper choice of bias current in the hsms-286a series can mini- mize variation over temperature. the detector circuits described earlier were tested over tempera- ture. the 915 mhz voltage doubler using the hsms-286a series produced the output voltages as shown in figure 15. the use of 3 m a of bias resulted in the highest voltage sensitivity, but at the cost of a wide variation over tempera- ture. dropping the bias to 1 m a produced a detector with much less temperature variation. a similar experiment was con- ducted with the hsms-286a series in the 5.8 ghz detector. once again, reducing the bias to some level under 3 m a stabilized the output of the detector over a wide temperature range. it should be noted that curves such as those given in figures 15 and 16 are highly dependent upon the exact design of the input impedance matching network. the designer will have to experi- ment with bias current using his specific design. figure 15. output voltage vs. temperature and bias current in the 915 mhz voltage doubler using the hsms-286a series. -55 -35 -15 5 85 45 65 output voltage (mv) temperature ( c) 25 40 80 60 120 100 input power = 30 dbm 3.0 a 1.0 a 10 a 0.5 a figure 16. output voltage vs. temperature and bias current in the 5.80 ghz voltage detector using the hsms-286a series. output voltage (mv) temperature ( c) 5 15 35 25 input power = 30 dbm 3.0 a 10 a 1.0 a 0.5 a -55 -35 -15 5 85 45 65 25
8 diode burnout any schottky junction, be it an rf diode or the gate of a mesfet, is relatively delicate and can be burned out with excessive rf power. many crystal video receivers used in rfid (tag) applications find themselves in poorly controlled environments where high power sources may be present. examples are the areas around airport and faa radars, nearby ham radio operators, the vicinity of a broadcast band transmitter, etc. in such environments, the schottky diodes of the receiver can be protected by a device known as a limiter diode. [8] formerly available only in radar warning receivers and other high cost electronic warfare applications, these diodes have been adapted to commercial and consumer circuits. hewlett-packard offers a complete line of surface mountable pin limiter diodes. most notably, our hsmp-4820 (sot-23) can act as a very fast (nanosecond) power- sensitive switch when placed between the antenna and the schottky diode, shorting out the rf circuit temporarily and reflecting the excessive rf energy back out the antenna. assembly instructions sot-363 pcb footprint a recommended pcb pad layout for the miniature sot-363 (sc-70 6 lead) package is shown in figure 17 (dimensions are in inches). this layout provides ample allowance for package placement by automated assembly equipment without adding parasitics that could impair the performance. [6] hewlett-packard application note 956-4, schottky diode voltage doubler. 0.026 0.075 0.016 0.035 figure 17. pcb pad layout (dimensions in inches). smt assembly reliable assembly of surface mount components is a complex process that involves many material, process, and equipment factors, including: method of heating (e.g., ir or vapor phase reflow, wave soldering, etc.) circuit board material, conductor thickness and pattern, type of solder alloy, and the thermal conductivity and thermal mass of components. components with a low mass, such as the sot-363 package, will reach solder reflow temperatures faster than those with a greater mass. hps sot-363 diodes have been qualified to the time-temperature profile shown in figure 18. this profile is representative of an ir reflow type of surface mount assembly process. after ramping up from room temperature, the circuit board with components attached to it (held in place with solder paste) passes through one or more preheat zones. the preheat zones increase the temperature of the board and components to prevent thermal shock and begin evaporat- ing solvents from the solder paste. the reflow zone briefly elevates the temperature sufficiently to produce a reflow of the solder. the rates of change of tempera- ture for the ramp-up and cool- down zones are chosen to be low enough to not cause deformation of the board or damage to compo- nents due to thermal shock. the maximum temperature in the reflow zone (t max ) should not exceed 235 c. these parameters are typical for a surface mount assembly process for hp sot-363 diodes. as a general guideline, the circuit board and components should be exposed only to the minimum temperatures and times necessary to achieve a uniform reflow of solder. time (seconds) t max temperature ( c) 0 0 50 100 150 200 250 60 preheat zone cool down zone reflow zone 120 180 240 300 figure 18. surface mount assembly profile.
9 package dimensions outline sot-363 (sc-70, 6 lead) 2.20 (0.087) 2.00 (0.079) 1.35 (0.053) 1.15 (0.045) 1.30 (0.051) ref. xx 0.650 bsc (0.025) 2.20 (0.087) 1.80 (0.071) 0.10 (0.004) 0.00 (0.00) 0.25 (0.010) 0.15 (0.006) 1.00 (0.039) 0.80 (0.031) 0.20 (0.008) 0.10 (0.004) 0.30 (0.012) 0.10 (0.004) 0.30 ref. 10 0.425 (0.017) typ. dimensions are in millimeters (inches) package marking code part number ordering information no. of part number devices container hsms-285a-tr1 [1] 3000 7" reel hsms-285a-blk [1] 100 antistatic bag hsms-286a-tr1 [2] 3000 7" reel hsms-286a-blk [2] 100 antistatic bag notes: 1. a = l or p only 2. a = l, p or r gu 1 2 3 6 5 4 pin connections and package marking notes: 1. package marking provides orientation and identification. 2. see electrical specifications for appropriate package marking.
10 device orientation user feed direction cover tape carrier tape reel end view 8 mm 4 mm top view ## ## ## ## note: ?#?represents package marking code. package marking is right side up with carrier tape perforations at top. conforms to electronic industries rs-481, ?aping of surface mounted components for automated placement.?standard quantity is 3,000 devices per reel. tape dimensions and product orientation for outline sot-363 (sc-70, 6 lead) p p 0 p 2 f w c d 1 d e a 0 8 max. t 1 (carrier tape thickness) t t (cover tape thickness) 5 max. b 0 k 0 description symbol size (mm) size (inches) length width depth pitch bottom hole diameter a 0 b 0 k 0 p d 1 2.24 0.10 2.34 0.10 1.22 0.10 4.00 0.10 1.00 + 0.25 0.088 0.004 0.092 0.004 0.048 0.004 0.157 0.004 0.039 + 0.010 cavity diameter pitch position d p 0 e 1.55 0.05 4.00 0.10 1.75 0.10 0.061 0.002 0.157 0.004 0.069 0.004 perforation width thickness w t 1 8.00 0.30 0.255 0.013 0.315 0.012 0.010 0.0005 carrier tape cavity to perforation (width direction) cavity to perforation (length direction) f p 2 3.50 0.05 2.00 0.05 0.138 0.002 0.079 0.002 distance width tape thickness c t t 5.4 0.10 0.062 0.001 0.205 0.004 0.0025 0.00004 cover tape
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for technical assistance or the location of your nearest hewlett-packard sales office, distributor or representative call: americas/canada: 1-800-235-0312 or 408-654-8675 far east/australasia: call your local hp sales office. japan: (81 3) 3335-8152 europe: call your local hp sales office. data subject to change. copyright ? 1997 hewlett-packard co. printed in u.s.a. 5966-2032e (10/97)

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