US 4,618,875 AGranted

Darlington transistor circuit

AssigneeRobert Bosch GmbH

InventorPeter Flohrs

Life of this patent

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Abstract

A Darlington transistor circuit having a power transistor and a driver transistor is proposed. The two transistors are monolithically integrated in a common substrate (10) by a planar process, the substrate forming the collector zones of the two transistors. On the main surface of the substrate (10) there is a passivation layer (13) covering this main surface with the exception of contact windows. The base-collector junctions of the two transistors are protected by a metal electrode (15), which is located above the passivation layer (13) and extends up to a stop ring (14), which is disposed beneath the passivation layer (13) in the substrate (10). The potential at the cover electrode (15) is adjustable with the aid of a voltage divider (16). (FIG. 3).

Claims12

Dependent claims

An external-field-insensitive Darlington transistor circuit, with adjustable junction breakdown voltage, having a power transistor (T1) and having a driver transistor (T2), the collector of which driver transistor is connected to the collector of the power transistor (T1) and the emitter of which driver transistor is connected to the base of the power transistor (T1), and in which circuit the power transistor (T1) and the driver transistor (T2) are monolithically integrated by a planar process in a common substrate (10) forming the collector zones of the two transistors (T1, T2),

wherein a first (11a) and a second zone (11b) are diffused into the substrate (10) from a main surface, the substrate (10) having a specified conductivity type and the first (11a) and second (11b) zones having the opposite conductivity type, said first and second zones (11a, 11b) respectively forming with the material of the substrate (10) a first (12a) and a second (12b) p-n junction and the base zones of the two transistors (T1, T2),
wherein, from the same main surface of the substrate (10), an emitter zone, having the same conductivity type as the basic material of the substrate (10) but a higher concentration of impurities, is diffused into each of said first and second base zones (11a, 11b), said emitter zones serving as the emitter zones (9a, 9b) of the respective transistors, and
wherein a substantially non-conductive passivation layer (13) covering this same main surface of the substrate (10), except for contact windows, is provided, comprising
a further annular zone (14), serving as a stop ring, diffused into the substrate (10) from the same main surface around the first (11a) and second (11b) base zones, said annular stop ring zone (14) having the same conductivity type as the basic material of the substrate (10) but a higher concentration of impurities;
a metal coating, serving as a cover electrode (15) and as a shield against external electric fields, applied atop the passivation layer (13), said metal coating (15) extending over a region between the base zones (11a, 11b) and the annular stop ring zone (14), and overlapping not only the annular stop ring zone (14), but also portions of the base zones (11a, 11b) adjacent to the annular stop ring zone (14), and
a voltage divider (16) monolithically integrated with said power (T1) and driver (T2) trransistors in said circuit, for adjusting the potential of the cover electrode (15) to a value dependent upon the desired breakdown voltage of the first and second p-n junction (12a, 12b), which value falls in a range defined by the potential of the first base zone (11a) and the potential of a portion of the substrate (10) located outside the first (11a) and second (11b) zones and having a conductivity type opposite from that of the first (11a) and second (11b) base zones, said voltage divider (16) including a voltage divider resistor (16a) and a tap (16b), and PG,14
wherein the tap (16b) is connected to the cover electrode (15),
the first end (19) of the voltage divider resistor (16a) is connected with one of the first zone (11a) and the second zone (11b), and the second end (20) of the voltage divider resistor (16a) is connected on a surface of said integrated circuit with a portion of the substrate (10) located outside the first (11a) and second (11b) zones, which portion has a conductivity type opposite from that of the first (11a) and second (11b) zones,
whereby said breakdown voltage can be adjusted, after fabrication of said integrated circuit, by varying where, on the surface thereof, one of said ends of said voltage divider resistor (16a) is connected.

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Dependencies are inferred from the claim text.

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Abstract

wherein a first (11a) and a second zone (11b) are diffused into the substrate (10) from a main surface, the substrate (10) having a specified conductivity type and the first (11a) and second (11b) zones having the opposite conductivity type, said first and second zones (11a, 11b) respectively forming with the material of the substrate (10) a first (12a) and a second (12b) p-n junction and the base zones of the two transistors (T1, T2),
wherein, from the same main surface of the substrate (10), an emitter zone, having the same conductivity type as the basic material of the substrate (10) but a higher concentration of impurities, is diffused into each of said first and second base zones (11a, 11b), said emitter zones serving as the emitter zones (9a, 9b) of the respective transistors, and
wherein a substantially non-conductive passivation layer (13) covering this same main surface of the substrate (10), except for contact windows, is provided, comprising
a further annular zone (14), serving as a stop ring, diffused into the substrate (10) from the same main surface around the first (11a) and second (11b) base zones, said annular stop ring zone (14) having the same conductivity type as the basic material of the substrate (10) but a higher concentration of impurities;
a metal coating, serving as a cover electrode (15) and as a shield against external electric fields, applied atop the passivation layer (13), said metal coating (15) extending over a region between the base zones (11a, 11b) and the annular stop ring zone (14), and overlapping not only the annular stop ring zone (14), but also portions of the base zones (11a, 11b) adjacent to the annular stop ring zone (14), and
a voltage divider (16) monolithically integrated with said power (T1) and driver (T2) trransistors in said circuit, for adjusting the potential of the cover electrode (15) to a value dependent upon the desired breakdown voltage of the first and second p-n junction (12a, 12b), which value falls in a range defined by the potential of the first base zone (11a) and the potential of a portion of the substrate (10) located outside the first (11a) and second (11b) zones and having a conductivity type opposite from that of the first (11a) and second (11b) base zones, said voltage divider (16) including a voltage divider resistor (16a) and a tap (16b), and PG,14
wherein the tap (16b) is connected to the cover electrode (15),
the first end (19) of the voltage divider resistor (16a) is connected with one of the first zone (11a) and the second zone (11b), and the second end (20) of the voltage divider resistor (16a) is connected on a surface of said integrated circuit with a portion of the substrate (10) located outside the first (11a) and second (11b) zones, which portion has a conductivity type opposite from that of the first (11a) and second (11b) zones,
whereby said breakdown voltage can be adjusted, after fabrication of said integrated circuit, by varying where, on the surface thereof, one of said ends of said voltage divider resistor (16a) is connected.

6 more elements