Younes Boulghassoul, Lloyd W. Massengill, and Ron Pease. Abstract. Carrier generation .... laser system (Clark-MXR CPA 1000) that pumps a tunable optical parametric ...... transistor, and thank Martha O'Bryan for graphics assistance. VIII.
Three-Dimensional Mapping of Single-Event Effects Using Two Photon Absorption Dale McMorrow, William T. Lotshaw, Joseph S. Melinger, Stephen Buchner, Younes Boulghassoul, Lloyd W. Massengill, and Ron Pease Abstract Carrier generation based on sub-bandgap two-photon absorption is used to perform three-dimensional mapping of the single-event transient response of the LM124 operational amplifier. Three classes of single-event-induced transients are observed for the input transistor Q20. A combination of experiment and transistor level modeling is used to assign the different classes of measured transients to charge collection across specific junctions. The largeamplitude, positive-going transients can not be assigned to a single junction, and are identified with a collector-substrate photocurrent. I. INTRODUCTION The picosecond laser has become an important tool for the investigation and understanding of single-event effects (SEEs) in microelectronic circuitry. The most common implementation of the pulsed laser technique is based upon the excitation of carriers in a semiconductor material using tightly focused, above-bandgap optical excitation [1]-[8]. Carrier generation is governed primarily by Beer's law absorption and, for a given material, the optical penetration depth is determined by the wavelength of the laser pulse. In recent years the pulsed laser has been used successfully in a range of investigations of SEE phenomena, including interrogation of the spatial and temporal aspects of singleevent upset (SEU) and single-event latch up (SEL) in a variety of digital circuits [1]-[3], investigation of the basic charge-collection mechanisms of individual transistors [4], and most recently as an essential tool for unraveling the complex SEE response of bipolar linear circuits [5]-[9]. Recently, a new method of laser-induced carrier generation for SEE applications based upon two-photon absorption (TPA) using high peak power femtosecond pulses at sub-bandgap optical wavelengths was introduced and demonstrated [10]. In two-photon absorption, the laser wavelength is chosen to be less than the bandgap of the semiconductor material such that no carriers are generated
Manuscript received 22 July, 2003. This work was supported by the Defense Threat Reduction Agency (DTRA) and the Office of Naval Research. Dale McMorrow and Joseph S. Melinger are with the Naval Research Laboratory, Code 6812, Washington, DC 20375 William T. Lotshaw is with SFA, Inc. Largo, MD 20774 Stephen Buchner is with QSS Group, Inc., Seabrook, MD 20706 Younes Boulghassoul and Lloyd W. Massengill are with the Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN 37235 Ronald L. Pease is with RLP Research, Albuquerque, NM 87122
(no optical absorption) at low light intensities. At sufficiently high intensities, however, the material can absorb two photons simultaneously to generate a single electron-hole pair [10]-[13]. Because carrier generation in the two-photon process is proportional to the square of the laser pulse intensity, significant carrier generation occurs only in the high-intensity focal region of the focused laser beam [10],[12],[13]. This enables charge injection at any depth in the structure, permitting both three-dimensional mapping of the SEE sensitivity of a device and backside illumination of circuits fabricated on silicon wafers. The two-photon absorption technique offers interesting possibilities for the study of analog single-event transient (ASET) phenomena in linear bipolar circuits. Preliminary measurements [10] on transistor Q20 of the LM124 quad operational amplifier using the TPA technique reveal a complex dependence of the induced transient on the depth profile of the deposited charge. In what follows, we utilize the two-photon technique to investigate the complicated dependence of the single-event transient response of the LM124 quad operational amplifier on depth, position, and deposited charge. II. TWO-PHOTON INDUCED SEE Details of the two-photon induced SEE technique are described in detail in [10]. Briefly, the primary expression responsible for carrier generation in a semiconductor material is, !MÐ
