An improved termination structure for silicon radiation ... - IEEE Xplore

IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 50, NO. 4, AUGUST 2003

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An Improved Termination Structure for Silicon Radiation Detectors With All-P-Type Multiguard and Cut-Line Implants Maurizio Boscardin, Luciano Bosisio, Andrea Candelori, Gian Franco Dalla Betta, Member, IEEE, Selenia Dittongo, Paolo Gregori, Claudio Piemonte, Irina Rachevskaia, Sabina Ronchin, and Nicola Zorzi

Abstract—A junction termination structure for silicon radiation detectors is investigated, featuring all-p-type multiguard and scribe-line implants, with metal field-plates providing complete coverage of the oxide upper surface above nonimplanted regions. The sensitive interface between oxide and n-type substrate is thus electrostatically screened from the external environment, resulting in improved long-term stability of the device and excellent insensitivity to ambient conditions both before and after X-ray and neutron irradiations. Careful design of the multiguard layout enables high-voltage operation to be achieved. With respect to a previously proposed structure, the adoption of alternate outward and inward field plates between adjacent rings allows a significant improvement in the voltage handling capability. Index Terms—Edge termination, field plates, multiguards, radiation effects, silicon ratiation detectors.

I. INTRODUCTION

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ILICON junctions are extensively used as radiation detectors in many fields of physical research, including highenergy physics and space experiments, high-resolution spectroscopy of X-rays and charged particles, and medical imaging applications [1]. Optimum operation of silicon detectors often requires high reverse bias to achieve substrate full depletion, as needed for maximum signal amplitude and minimum charge collection time. Besides coping with junction breakdown problems, the detector design should be optimized to enhance the insensitivity to environmental conditions such as temperature, humidity, contaminants, etc. In particular, instabilities in the long-term behavior are mainly concerned with negative charge Manuscript received December 2, 2002; revised March 3, 2003. This work has been supported in part by the National Institute for Nuclear Physics of Italy (INFN) and by the “Provincia Autonoma di Trento” under Contract “Fondo per i progetti di ricerca 2002—progetto PDX.” M. Boscardin, P. Gregori, C. Piemonte, S. Ronchin, and N. Zorzi are with Divisione Microsistemi, ITC-IRST, I-38050 Povo (Trento), Italy (e-mail: [email protected]). L. Bosisio and S. Dittongo are with the Dipartimento di Fisica, Università di Trieste, I-34128 Trieste, Italy, and also with INFN-Trieste, I-34128 Trieste, Italy (e-mail: [email protected]). A. Candelori is with INFN-Padova, I-35131 Padova, Italy (e-mail: [email protected]). G. F. Dalla Betta is with the Dipartimento di Informatica e Telecomunicazioni, Università di Trento, I-38050 Povo (Trento), Italy, and also with Divisione Microsistemi, ITC-IRST, I-38050 Povo (Trento), Italy (e-mail: [email protected]). I. Rachevskaia is with the Divisione Microsistemi, ITC-IRST, I-38050 Povo (Trento), Italy, and also with INFN-Trieste, Trieste, Italy (e-mail: [email protected]). Digital Object Identifier 10.1109/TNS.2003.814577

Fig. 1. Schematic cross section of a pair of adjacent guard rings in (a) the termination structure of [4] and (b) in the modified structure (not to scale). Geometrical dimensions are given in micrometers.

migration and trapping at the oxide external surface, which can partially compensate and, in some cases, even exceed the positive oxide charge [2]. As a result, the space-charge region can extend laterally and finally reach the heavily damaged cut edge of the substrate, causing a dramatic increase in the leakage current [3]. To counteract these effects, detector designs often fea-region along the edge (including the scribe line), ture an having a width comparable to the wafer thickness and placed at a minimal safety distance (typically of the order of a few hun), from the outermost region. In addition or as dreds of an alternative, many designs make use of multiple guard rings, which, besides improving long-term stability, also enhance the breakdown voltage (see [4] and references therein). We have previously reported an all-p-type termination structure with several concentric floating guard rings (the last of which coinciding with the scribe line implant) equipped with metal field plates extending inward and overlapping the implant of the preceding ring [5]. In this way, the metal field plates cover all of the sensitive interface between oxide and n-type substrate, providing an electrostatic screen from the external environment. This feature yields improved long-term stability of the device and excellent insensitivity to ambient conditions [2]. An additional advantage, with respect to those designs, which include region along the device edge, is fabrication process siman plification, since the related lithographic and implantation steps can be omitted; this also eliminates the risk of process defects implants, that might overlap implants related to parasitic causing early breakdown problems [6]. The performance of this kind of structure largely depends on the number of floating rings that can be fitted in a given space between the detector and the cut edge. This number is limited mainly by the minimum width of the implanted rings, which, in turn, is constrained by the need for providing a contact area to

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Fig. 2.


Schematic cross section of the modified all-p-type termination structure (not to scale). TABLE I DISTANCES (IN MICROMETERS) BETWEEN GUARD RINGS OF THE FOUR NEW LAYOUTS

the field plate, a sufficient overlap with the field plate of the next ring and finally a safe distance between two adjacent metal rings [see Fig. 1(a)]. Since large area silicon detectors are most often fabricated making use of proximity-type mask aligners, the design rules are relatively relaxed, resulting in a minimum width of the rings which can be of order of a few tens of micrometers; for the fabrication process employed in [5], we adopted a safe . width of 25 In this paper, we present an improved design, in which the adoption of alternate outward and inward field plates between adjacent rings allows an enhancement in the voltage handling capability both prior and after X-ray and neutron irradiations, while preserving excellent insensitivity to ambient conditions. II. DEVICE DESCRIPTION In the proposed modified design, the field plates between the rings extend alternately outward and inward [see Fig. 1(b)] so that only every second implanted ring needs to be contacted by a metal ring. As a result, almost twice the number of implanted rings can be fitted within the same area along the detector edge, thus significantly improving the high-voltage behavior of the structure. The proposed structure is sketched in Fig. 2: the outermost biased guard ring of the detector, referred to as the large guard (LG) is surrounded by several concentric floating guard rings, the last of which coincides with the scribe line implant. Every second floating ring is provided with a metal field plate extending both inward and outward to overlap the two adjacent ring implants. With the help of 2-D numerical device simulations, performed with the program DESSIS[7], we designed four 20-ring structures (N1–N4) that can provide a good tradeoff between and area consumption maximum operating voltage . In all structures, the LG and scribe line implant are 100 wide, whereas the width of the intermediate for the odd-numbered rings and 12 for implants is 14 the even-numbered ones. The distances between the implanted rings have been chosen differently for the gaps covered with outward field plates and those covered by inward field plates,

Fig. 3. Micrograph of the bottom-right corner of a N2 structure, showing diode, large-guard, multiguards, and scribe-line.

in order to take into account the different behavior of these structures in relation to the need for minimizing outward propagation of the space charge region [8]. The four layouts differ in the distance between the rings, which increases every third pair of rings moving from LG to the edge of the device, following the progression indicated in Table I. These layouts were implemented as termination struc- diodes having a total die size of tures of single-sided . Devices were fabricated at IRST (Trento, Italy) 3.5 3.5 on n-type, 300 thick, FZ, wafers, with resistivities ranging from 5 to 30 . Fig. 3 shows the micrograph of the bottom-right corner of a N2 structure. Details on the fabrication technology can be found in [9]. Also the best two layouts presented in [5], i.e., S2 and S4, featuring a comparable value of the overall distance between the large guard and the , were implemented as termination scribe-line structures for other test diodes in the same wafers in order to allow a direct comparison between the new design and the previous one.

BOSCARDIN et al.: IMPROVED TERMINATION STRUCTURE FOR SILICON RADIATION DETECTORS

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TABLE II EXPERIMENTAL VALUES OF THE MAIN TECHNOLOGICAL PARAMETERS EXTRACTED FROM TEST STRUCTURES MADE ON DIFFERENT TYPES OF WAFERS: ), OXIDE THICKNESS (t ), OXIDE-CHARGE DENSITY (N ), BULK-GENERATION LIFETIME ( ), SUBSTRATE-DONOR CONCENTRATION ( SURFACE-GENERATION VELOCITY (s ). AVERAGE AND STANDARD DEVIATION VALUES REFERRING TO 8 SAMPLES PER WAFER TYPE ARE REPORTED

N

III. RESULTS AND DISCUSSION A. Pre-Irradiation Measurements The main technological parameters were extracted from dedicated test structures belonging to the same wafers of the considered devices. The resulting values are summarized in Table II for three different wafer types. In particular, data refer to two complete sets of devices per wafer, with four wafers per type. The electrical characterization of the devices was carried out by means of a probe-station and semiconductor test equipment controlled by custom developed Labview programs. All measurements were performed at room temperature and, unless otherwise stated, within the humidity range 30–40%. To test the voltage-handling capabilities of the proposed was measured as a funcstructures, the large-guard current by using two different setups: tion of the reverse voltage (a) with scribe-line floating and (b) with scribe-line shorted to the backside contact. These two types of measurements enable the evaluation in a fast and reliable way prior to wafer dicing, respectively, of the junction breakdown voltage and the bias voltage corresponding to the onset of punch-through between the large guard and the scribe line implants [5]. Fig. 4 shows the experimental currents of the large guard and of the outer ring for a N2 structure made from a type-A wafer. The onset of punch-through between the LG and the outer ring is clearly indicated by the exponential increase in both currents, which start deviating from their normal low-voltage behavior (essentially governed by bulk generation), and finally merge into one curve at high voltage when punch-through becomes the dominant conduction mechanism. As a matter of fact, in all cases punch-through was found to be the limiting mechanism both for the new structures and the two versus old ones. As an example, Fig. 5 shows typical characteristics for six structures belonging to the same wafer of type A. A substantial improvement is evident for the new structures, which can be operated at a reverse voltage up to about 40 V higher with respect to the best of the old ones (see N2 and S2 in Fig. 5). Minor changes in the device static characteristics have been observed after wafer dicing. The impact of variations in substrate resistivity on the device performance is clearly observed in Fig. 6, showing the versus curves of three N2 structures belonging to three types of wafers having a substrate donor concentration ranging to 7.5 . As can be seen, the from 1.6 voltage handling capability of the device is clearly increased at higher substrate dopings, as a result of a higher punch-through voltage between adjacent rings. This aspect should be carefully considered when designing termination structures for more re-

Fig. 4. Experimental large-guard (I ) and outer guard ring (I ) currents as a function of reverse-bias voltage for a N2 structure with scribe-line kept at the same backside contact potential.

Fig. 5. Experimental large-guard current (I ) as a function of reverse-bias voltage (V ), measured with scribe-line shorted to the backside contact on six different structures from a type-A wafer.

sistive substrates, that might require the guard number and/or the guard spacings to be suitably adapted. Following the same approach used in [5], we derived the adi, where mensional function is the slope of the versus curves. In other words, represents the sensitivity of the LG current to the reverse voltage. By adopting the same limit value as in [5], we calculated the maximum voltage , for which . The resulting values are summarized in Table III. Regardless of the wafer type, the new structures exhibit values higher than those of the old ones. In particular, N2 is the best device, its values exceeding those of the best old device (S2) by about 45 V.

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Fig. 6. Experimental large-guard current (I ) as a function of reverse-bias voltage (V ) for three N2 structures fabricated on wafers having different substrate doping concentration.

B. X-Ray Irradiation In order to check the behavior of the structures in the presence of a much higher oxide-charge density, an irradiation test with X-rays was performed at the Semiconductor Irradiation Facility (Seifert RP-149) available at the INFN National Laboratory, Legnaro, Italy [10]. Six devices (one per layout) made from a type-A wafer were irradiated up to a total dose of about 2Mrad(Si) by means of an X-ray tube with a tungsten target, having an energy peak at 10 keV. The dose rate was about 375 rad/s(Si), for a total irradiation time of 90 min. During irradiation, devices were kept unbiased. Also two groups of test structures belonging to the same wafers (MOS capacitors and gated-diodes) were irradiated, so as to extract the post-irradiation oxide charge and surface generation velocity. Measurements were carried out one day after irradiation. After that, annealing was performed in order to reduce the amount of oxide-charge density [11]. Devices were first kept for 13 days at room temperature, without bias, and measured again. Then, two annealing cycles at 120 were performed, the first one for 20 min and the second one for 30 min, repeating the measurements after each step. Details on the surface parameters extracted from test structures in all measurement conditions considered are reported in Table IV. versus characteristics for the Fig. 7 shows typical six different structures measured one day after X-ray irradiation. Devices exhibit a much higher current at low voltage as a interface. At result of an increased generation at the the same time, an improvement is observed in the device voltage handling capability, both for the old and new designs, the latter showing an uniform trend with minor differences between their – curves. The behavior of the old structures can be explained by taking into account the radiation induced increase in the punch-through voltage between the rings [12], [13]. At this point, it is worth remembering that these structures feature 12 rings and the distance between two adjacent rings increases every third ring moving from LG to the edge of and the device, following the progressions 12, 18, 24, 30 for S2 and S4, respectively [5]. Hence, 15, 20, 25, 30 even a small increase in the punch-through voltage between


adjacent rings can cause the observed overall improvement in the device operational limit of about 25 V. As for the new structures, the presence of outward-directed field plates, completely covering the gap between the implanted rings, makes them susceptible to the turn-on of parasitic MOSFET’s between the rings. The voltage difference between two rings separated by a gap covered with an outward field plate will thus be limited by the threshold voltage of the parasitic MOSFET, which may happen to be smaller than the punch-through voltage [8]. This is likely to be the case before irradiation, at least for the most external guard-rings that, due to the increasingly larger spacing between them, feature a higher punch-through voltage, whereas the threshold voltage, as measured on a MOSFET test structure, is approximately in the range 12–13 V for type-A wafers, depending on substrate bias. After irradiation, due to the higher oxide-charge density, both the punch-through voltage and the threshold voltage of the parasitic MOSFET increase, thus enhancing the operational voltage limit coming from the onset of conduction between LG and the scribe line. However, taking into account the behavior of S2–S4, an increase of a few volts in the punch-through voltage between adjacent rings can be estimated, much lower than the increase in the threshold voltage, in the order of 60 V. Hence, after irradiation, surface conduction between the rings is suppressed. Noticeably, also after irradiation, all structures do not exhibit avalanche breakdown at junction edges within the considered voltage range, punch-through being still the limiting factor, so that these structures are expected to yield improved voltage handling capabilities at even higher ionizing radiation doses. The annealing effect on the device behavior can be appreciated with the aid of Fig. 8, which shows the versus curves of a N2 structure measured in all the different conditions. The annealing results in a current decrease before the onset of punch-through, which is mainly due to the decrease in the surface generation velocity (see Table IV), whereas the operational limit is slightly reduced. Similar behavior was observed for all the other designs. values, expressed with a 5 V resolution, are summaThe values higher rized in Table V. The new structures exhibit than those of the old ones, with N2 still exhibiting the best performance. C. Neutron Irradiation In order to assess the device behavior in the presence of bulk damage, as previously reported in [5], a neutron irradiation experiment was performed at ENEA-Frascati, Italy [14]. During irradiation, devices were kept unbiased. One set of samples from 1-MeV type-B wafers was irradiated up to a fluence of 1 . This relatively low fluence, insuffiequivalent cient to cause substrate type inversion, corresponds to the total fluence expected for ALICE microstrip detectors [15]. After irradiation, devices were kept at room temperature for ten days before being measured. versus curves measured after Fig. 9 shows the neutron irradiation. The increase in the leakage current due to bulk damage is evident. In this respect, a damage constant was extracted from the diode current, in good agreement with generally accepted values [16].


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TABLE III EXPERIMENTAL VALUES OF V (V ) FOR ALL THE CONSIDERED STRUCTURES MEASURED ON THE THREE TYPES OF WAFERS. AVERAGE AND STANDARD DEVIATION VALUES REFERRING TO 8 SAMPLES PER WAFER TYPE ARE REPORTED. OLD STRUCTURES WERE NOT AVAILABLE ON TYPE-C WAFERS

TABLE IV AVERAGE EXPERIMENTAL VALUES OF THE FLAT-BAND VOLTAGE (V ), OXIDE-CHARGE DENSITY (N ) AND SURFACE-GENERATION VELOCITY (s ) MEASURED ON TEST STRUCTURES BEFORE X-RAY IRRADIATION, 1 DAY AFTER X-RAY IRRADIATION UP TO A TOTAL DOSE OF 2 MRAD(SI), AND AFTER EACH OF THE PERFORMED ANNEALING STEPS

: as a matter of fact, a value of about 1.3 was measured from diode capacitance-voltage measurements. values are still Despite post-irradiation degradation, these high enough to allow for device operation at a voltage that is well beyond the full-depletion voltage, which, by effect of the irradiation, has decreased from about 11 V to 9 V. Again, N2 is the structure that exhibits the best post-irradiation voltage-hanvalue of 100 V. Nevertheless, the dling capabilities, with a use of the proposed termination schemes should be carefully considered in those applications involving a large amount of displacement damage: in fact, near the fluence of space charge sign inversion, the voltage handling capability could may go through a minimum that can be smaller than the full depletion voltage. Fig. 7. Experimental large-guard current (I ) as a function of reverse-bias voltage (V ) measured on six different structures from a type-A wafer 1 day after X-ray irradiation up to a total dose of 2 Mrad(Si).

Fig. 8. Experimental large-guard current (I ) as a function of reverse-bias voltage (V ) measured on a N2 structure from a type-A wafer before X-ray irradiation, one day after X-ray irradiation and after each of the performed annealing steps.

In all structures, the voltages were found to degrade with respect to their pre-irradiation values, as reported in Table VI. This trend is due to the decrease in the punch-through voltage caused by the decrease in the effective doping concentration,

D. Stability Measurements The stability of the leakage currents was also tested at room temperature on a few device samples for 14 h or longer, with current data sampling every 10 min. All of the tested devices exhibited excellent stability, with maximum LG current variations lower than 1.5% in the last 5 h of the measurements. As an curves as a function of time in example, Fig. 10 shows the N2 structures from different wafer types measured in three different conditions: before irradiation, one day after X-ray irradiation (before annealing), and ten days after neutron irradiation. For these measurements, devices were reverse biased at 100 V, i.e., close to their operational limit, and keeping the scribe-line at the same potential as the backside contact. Noticeably, only minor variations of the leakage currents were observed during the measurements as a result of small temperature fluctuations. Because the interface area between the oxide and the silicon substrate is completely covered by metal field plates, the structure is expected to be unaffected by ambient conditions such as ionic contaminants or ambient humidity. In order to check this point, the leakage current of a few devices, biased close to their operational limit, has been monitored over a 24 h period under changing humidity levels. As an example, Fig. 11 shows the time evolution of the humidity and of the large guard cur. The device was prelimrent in a N2 structure at inarily stabilized by flowing dry nitrogen through the test box

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TABLE V EXPERIMENTAL VALUES OF V (V ) FOR SIX STRUCTURES FROM A TYPE-A WAFER MEASURED BEFORE X-RAY IRRADIATION, ONE DAY AFTER X-RAY IRRADIATION UP TO A TOTAL DOSE OF 2MRAD(SI), AND AFTER EACH OF THE PERFORMED ANNEALING STEPS

Fig. 9. Experimental large-guard current (I ) as a function of reverse-bias voltage (V ) measured on six different structures from a type-B wafer ten days after neutron irradiation to a fluence of 1 10 cm .

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Fig. 10. Experimental large-guard current at V = 100 V as a function of time in N2 structure from different wafer types before and after X-ray and neutron irradiation.

TABLE VI EXPERIMENTAL VALUES OF V (V ) FOR SIX STRUCTURES FROM A TYPE-B WAFER MEASURED BEFORE IRRADIATION AND TEN DAYS AFTER NEUTRON IRRADIATION UP TO A FLUENCE OF 1 10 cm

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for one night, bringing relative humidity (RH) down from 31% to about 1%. The last hour of this time period is considered in , and Fig. 11. After that, the flow has been changed to wet the RH gradually increased to 90%. In spite of this dramatic increase in the humidity level, the leakage current of the device, after some transient changes (not exceeding 0.5 nA), shows a clear stabilization trend at a saturation level which is higher that the starting value by about 40%, a fact that can probably be attributed to a small ionic current flowing between the large guard and the scribe line metal pads along the outer device surface. This shows that the device is stable under rather extreme variations in ambient humidity. IV. CONCLUSION An improved ”all-p-type” termination scheme, consisting of floating guard rings with alternate inward and outward metal field plates completely covering the gap between the implanted rings, has been reported. The structure is intended for detector long-term stability enhancement even in adverse ambient conditions and for fabrication-process simplification. The proposed devices have shown a very stable behavior both before and after X-ray and neutron irradiation, as well as in the presence of humidity changes over a wide range of

Fig. 11. Experimental large-guard current at V = 120 V as a function of time in a N2 structure subjected to different humidity concentrations.

values (1%–90%). Moreover, the voltage handling capability has been significantly improved with respect to a previous . design featuring a comparable area occupation A systematic characterization work aiming at comparing the stability behavior of the proposed structures to that of control implant along the edge structures featuring: 1) a standard (including the scribe line) and 2) no implant along the edge is in progress. It should be stressed that the optimal layout of the termination structure is dependent on the technological parameters characterizing the substrate material and the fabrication process so that the design may require to be varied from manufacturer to manufacturer, or for material batches of different resistivity and/or orientation. The operational environment of the device,


and particularly the expected radiation field, should also be carefully considered. In this respect, the previous design, featuring only inward-directed field plates, appears to be more suited for extremely low substrate doping and/or oxide charge densities, in applications with moderate levels of ionizing radiation. The new design, which facilitates the fitting of a larger number of rings within the same area, appears to be preferable in the other cases, in particular where junction breakdown could be a limiting factor (as for large depletion voltages resulting from relatively high substrate doping and/or large thickness) and for high doses of ionizing radiation (where the turn-on of parasitic MOSFETs is suppressed). Further work is under way to gain deeper insight into these issues. Moreover, additional neutron irradiation experiments are foreseen to investigate the device behavior near the fluence of space charge type inversion.

ACKNOWLEDGMENT The authors would like to thank Dr. M. Pillon and Dr. M. Angelone, ENEA-Frascati, Italy, for performing neutron irradiations. They would also like to thank Dr. A. Litovchenko INFNPadova, Italy, for the kind assistance during the X-ray irradiation experiment, as well as Prof. G. Verzellesi, University of Modena and Regia Emilia, Italy, for many fruitful discussions.

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[2] A. Longoni, M. Sampietro, and L. Strüder, “Instability of the behavior of high resistivity silicon detectors due to the presence of oxide charges,” Nucl. Instrum. Methods, vol. A288, pp. 35–43, 1990. [3] A. Bischoff et al., “Breakdown protection and long-term stabilization for Si-detectors,” Nucl. Instrum. Methods, vol. A326, pp. 27–37, 1993. [4] M. Da Rold et al., “Study of breakdown effects in silicon multiguard structures,” IEEE Trans. Nucl. Sci., vol. 46, pp. 1215–1223, Aug. 1999. [5] G. F. Dalla Betta et al., “A novel silicon microstrip termination structure with all-p-type multiguard and scribe-line implants,” IEEE Trans. Nucl. Sci., vol. 49, pp. 1712–1716, Aug. 2002. [6] M. Boscardin, L. Bosisio, G. F. Dalla Betta, P. Gregori, I. Rachevskaia, and N. Zorzi, “Development of ALICE microstrip detectors at IRST,” Nucl. Instrum. Methods, vol. A461, pp. 188–191, 2001. [7] DESSIS6.0 Reference Manual, Integrated Systems Engineering (ISE) AG, Zürich, Switzerland, 1999. [8] B. S. Avset and L. Evensen, “The effect of metal field-plates on multiguard structures with floating p guard rings,” Nucl. Instrum. Methods, vol. A 377, pp. 397–403, 1996. [9] G. F. Dalla Betta, M. Boscardin, L. Bosisio, I. Rachevskaia, M. Zen, and N. Zorzi, “Development of a fabrication technology for double-sided ac-coupled silicon microstrip detectors,” Nucl. Instrum. Methods, vol. A460, pp. 304–313, 2001. [10] D. Bisello et al., “Irradiation facilities for electronic devices and systems at the INFN national laboratory of legnaro,” in Proc. RADECS, Padua, Italy, Sept. 2002, pp. 205–208. [11] T. P. Ma and P. V. Dressendorfer, Ionizing Radiation Effects in MOS Devices and Circuits. New York: Wiley, 1989. [12] M. Laakso, P. Singh, E. Engels Jr., and P. F. Shepard, “Operation and radiation resistance of a FOXFET biasing structure for silicon strip detectors,” Nucl. Instrum. Methods, vol. A 326, pp. 214–221, 1993. [13] N. Bacchetta et al., “Radiation tolerance of the FOXFET biasing scheme for ac-coupled Si microstrip detectors,” IEEE Trans. Nucl. Sci., vol. 40, pp. 1602–1609, Dec. 1993. [14] M. Martone, M. Angelone, and M. Pillon, “The 14 MeV frascati neutron generator,” J. Nucl. Mater., vol. 212–215, pp. 1661–1664, 1994. [15] “ALICE Technical Design Rep. (TDR4) of the Inner Tracking System,”, CERN/LHCC 99-12, 1999. [16] “3rd RD48 Status Rep.,” The ROSE Collaboration, CERN/LHCC 2000-009, 1999.